Detached Garages - a recurring theme

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  #1  
Old 01-11-01, 01:21 PM
s1nuber
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I thought that I would throw in my two cents, then again, two cents may be overpriced. Here it goes anyway. The upper 3/4 or so of this post is technical stuff on how I support my opinion, so if you just need to know how to wire a detached garage by code, head to the bottom!

All references are from the 1999 NEC.

It is important to remember that there is a major difference between a GROUNDED conductor and a GROUNDING conductor. I will refer to all grounded conductors in this post as nuetrals. When I use the words 'ground' or 'grounding' I will be referring to conductors that under normal conditions, do not carry current, and are intended for equipment, or other grounding uses.

The first thing to look at is the type of wire to the detached garage. Are they service conductors, feeder conductors, or branch circuit conductors?

100 A.) Branch Circuit - The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

100 A.) Feeder - All circuit conductors between the service equipment, the source of a seperately derived system, or other power supply source and the final branch-circuit overcurrent device.

100A.) Service conductors - The conductors from the service point [the point of connection between the serving utility and the premises wiring]to the service disconnecting means [A device, or group of devices, or other means by which the service can be disconnected from the serving utilities' power source].

In most instances, the conductors will not be service conductors, as there will likely be some form of overcurrent device between the service point and the detached garage. This effectively eliminates article 230 from discussions regarding detached garages. I have seen some instances contrary to this, most notably some farm installations, commercial buildings, and apartment complexes. The service conductor possibility should not be discounted, it is just not very common for residential use. It should be noted that if this does apply to you, article 230-3 states that "one building or other structure not to be supplied through another", so all service conductors would have to be run outside of the building.

The governing article now becomes 225 Outside branch circuits and feeders. Specifically section B. More than one building or other structure.
225-30 Number of supplies. Where more than one building or other structure is on the same property and under single management, each building or other structure served shall be supplied by one feeder or branch circuit unless permitted in (a) through (e). A detached residential garage will rarely meet these exceptions (a different voltage or phase requirement, or loading requirements would be the most common in my experience.)

This article allows either a feeder or a branch circuit to be run to our detached garage. It also gives us guidance for disconnecting means, location, number of disconnects, grouping of disconnects, type, identification, and access requirements. Two items are very important here.

225-36. Suitable for service equipment. The disconnecting means specified in section 225-31 shall be suitable for use as service equipment. EXCEPTION: For garages and outbuildings on residential property; a snap switch or a set of 3-way or 4-way snap switches shall be permitted as the disconnecting means. This does not mean that a detached garage will now have service equipment, just that the disconnecting means is rated for use as service equipment. The exception is important for single branch circuit installation.

225-39. Rating of disconnect. The feeder or branch circuit disconnecting means shall have a rating of not less than the load to be carried, determined in accordance with article 220. In no case shall the rating be lower than specified in (a), (b), (c), or (d).
(a) single branch circuit - 15 amps
(b) two circuit installations (generally not allowed, but possible) - 30 amps
(c) one family dwelling - 100 amps
(d) all others - 60 amps.
(a) through (d) above are paraphrased, but we have two general choices for a detached garage. One is to run a single branch circuit rated 15 amps minimum. The other is to run a feeder which must be rated 60 amps minimum, including a panel in our garage.

So that leaves a feeder or a branch circuit. If you are only running a single circuit, with no overcurrent devices in the detached garage, you have a branch circuit.

We need to look at grounding requirements for a branch circuit.

250-32 Two or more buildings or structures supplied from a common service.
(a) Grounding electrode. Where two or more buildings or structures are supplied from a common ac service by a feeder(s) or branch circuit(s), the grounding electrode(s) required in part C of this article at each building or structure shall be connected in the manner specified in (b) or (c). Where there are no existing grounding electrodes, the grounding electrode(s) required in part C of this article shall be installed.
EXCEPTION: A grounding electrode at separate buildings or structures shall not be required where only one branch circuit supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the non-current carrying parts of all equipment.

So, by the exception, if you run a single branch circuit (typically lights and outlets only) to your detached garage, you must run three wires (hot, nuetral, & grounding), with no overcurrent protection in the garage, and no ground rod. We will need overcurrent protection at the house for this circuit, and we will need a disconnect (a snap switch will work perfectly according to 225-36) located on the garage.

The other typical installation is a feeder to the detached garage. If the garage needs multiple circuits, a feeder will be the way to get power to the garage. This means a disconnecting means will be needed at or on the garage by 225-32. An exception allows "For installations under single management, where documented safe switching procedures are established and maintained for disconnection, the disconnecting means shall be permitted to be located elsewhere on the premises." No residential application can meet this requirement, and it wouldn't be worth the trouble compared to installing a disconnect anyway. Remember that according to 225-36 this disconnect must be rated for use as a service disconnect, and can feed a panel, or be part of a panel.

We now have to look at grounding for a detached garage with a 60 amp feeder (minimum). Is this garage feeder panel a seperately derived system (250-30), or is it two or more buildings or structures supplied from a common service (250-32)?

100 A.) Seperately derived system - A premises wiring system whose power is derived from a battery, a solar photovoltaic system, or from a generator, transformer, or converter windings, and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.

In the situation above, the detached garage does not have a seperately derived system. Both hots, as well as the nuetral are solidly connected to the house panel, so we can eliminate article 250-30 from use for our garage. It should be noted that is is possible to have a seperately derived electrical system in your garage. A stand alone generator, self contained solar system, or a transformer of some kind that supplies the detached garage exclusively would be some examples. These options are all very pricey, and are not common, in fact they are extremely rare in my experience, if not unheard of.

So, according to 250-32 (see above), the required grounding electrode per part C of article 250 shall be connected in one of two ways per (b) grounded systems, or (c) ungrounded systems. Whether you have a single branch circuit, or a feeder circuit brought from the house panel, you have a grounded system. This refers to the grounded nuetral connection, not the grounding conductor, so 250-32 part (c) does not apply to a detached residential garage.

250-32 (b) Grounded systems. For a grounded system at the separate building or structure, the connection to the grounding electrode and grounding or bonding of equipment, structures, or frames required to be grounded or bonded shall comply with either (1) or (2).

(1) Equipment grounding conductor. An equipment grounding conductor as described in section 250-118 shall be run with the supply conductors and connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equuipment, structures, or frames required to be grounded or bonded. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).
This means that a four wire feeder (two hots, one nuetral, and one grounding wire)is preferred. If you run four wires, the nuetrals and the grounding conductors must be kept seperate, and the nuetral shall not be connected to the grounding electrodes, or their conductors at the detached garage.

(2) Grounded conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, and (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved, and (3) ground fault protection of equipment has not been installed on the common ac service, the grounded circuit conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded.
This means that a three wire feeder can be used for the garage, only if no equipment grounding conductor is run, and there are no continuous metal paths between both structures (such as a metal water pipe for a hot tub, or a metal raceway for the feeder conductors), and the common service at the house does not have gfci protection (this means you entire house has gfci protection). Excellent drawings of these situations are available in the 1999 NEC Handbook on page 174.

It should be noted that 250-32 (d) does not apply as no residence has established disconecting procedures as discussed above.

This leaves three general methods of providing power to a detached residential garage, these are not every possible method, but certainly are the easiest and most common.

1) Install a single branch circuit from the main house, with overcurrent protection at the source, three wires (one hot, one nuetral, one grounding) in the circuit to a disconnect (snap switch is allowed) located at/in the garage. No overcurrent devices in the garage (fuses or circuit breakers). The circuit must be no smaller than 15 amps. No ground rod is required, nor any connections to any grounding electrodes if present.

2) Install a 60 amp (minimum) three wire (two hots, one nuetral) feeder circuit from the main house. Install overcurrent protection at the house, as well as a service disconnect rated disconnect at the garage. Install a grounding rod, grounding electrode conductor and connect them to the grounded conductor at the garage disconnect. This option may not have any common grounding from house to garage such as metal raceways, or metal water pipes that originate or continue to the house. This option also may not have a sevice panel gfci protection at the common service. A panel with individual branch circuit overcurrent protection will be needed at the garage as well.

3) Install a 60 amp (minimum) four wire feeder (two hots, one nuetral, one grounding conductor) from the main house. Install overcurrent protection at the house, as well as a service disconnect rated disconnect at the garage. Install a grounding rod, grounding electrode conductor and connect them to the grounding conductor at the garage disconnect. Do not connect the nuetral and the grounding conductor to each other, or to the same bus. A panel with individual branch circuit overcurrent protection will be needed at the garage as well.

That's my two cents, send all payments to Santa Claus as a charitable donation c/o S1nuber.

[Edited by s1nuber on 01-21-01 at 10:28]
 
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  #2  
Old 01-11-01, 05:28 PM
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Holy cow, s1nuber! A novelist in our midst. I haven't even read the whole thing yet, but I plan to print it out for future reference, mainly because when I digest a rule I forget where I found it later. Boy, with that much enthusiasm to sit down and write all that I gotta question just how much coffee you drink! Oh, and thanks.

Juice
 
  #3  
Old 01-11-01, 06:15 PM
Wgoodrich
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I see nowhere in 250-32-b-1 that says you must install a ground rod at the second building. Would you please post a copy of the section requiring this ground rod at the second building when the main building is supplying the grounding source?

Would you justify your requiring the second ground source at the second building creating a second grounding source to both buildings, that is not bonded together with all other grounding sources by a grounding service conductor as required by the NEC?

I see no bonding together of the two grounding sources except by an undersized equipment gouding conductor run with the feeder and the earth itself. Both being a Code violation.

Still see no agreement on this subject.

Stubborn ain't I, HE HE.

Wg
 
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Old 01-12-01, 07:43 AM
s1nuber
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Hey WG! Great observations on the grounding rod, I didn't get too in depth on that one due to the length of the post, so here it goes...

Article 250 part C. Grounding electrode system and grounding electrode conductor

250-50 Grounding electrode system. If available on the premises at each building or structure served, each item (a) through (d), and any made electrodes in accordance with sections 250-52(c) and (d), shall be bonded together to form the grounding electrode system.
(a) Metal underground water pipe (supplemental electrode required)
(b) Metal frame of the building or structure (where effectively grounded)
(c) Concrete cased electrode
(d) Ground ring

This means that at every building or structure served with electricity has to have a grounding electrode system. Every one of the four items above has to be bonded together to form the grounding electrode system. A detached garage generally has none of the four electrodes, so 250-52 is applicable.

250-52 Made and other electrodes. Where none of the electrodes specified in section 250-50 is available, one or more of the electrodes specified in (b) through (d) shall be used.
(a) Metal underground gas piping system - DO NOT USE AS A GROUNDING ELECTRODE
(b) Other local metal underground systems or structures (metal septic tanks or metal sewage systems - not combustible gas systems)
(c) Rod and pipe electrodes (standard 8 foot ground rods etc.)
(d) Plate electrodes
(e) Aluminum electrodes - SHALL NOT BE USED

So, for a detached garage, the four main grounding electrodes will generally not be available, the easiest and most common grounding electrode will be a made electrode per 250-52(c). This is required at EVERY BUILDING OR STRUCTURE SERVED by electricity, and is excluded in only one instance that I am aware of: a seperate building or structure that only has a single branch circuit fed from a common ac service where the grounding conductor is brought with the circuit [see 250-32 (a) exception]. (It should be noted that there are some requirements with a made electrode such as minimum resistance per 250-56 that may require multiple rods to be installed).

These same requirements are echoed in 250-32 (a): "Where two or more buildings ar structures are supplied from a common ac service by a feeder or branch circuit, the grounding electrode required in part C [250-50]of this article at each building or structure shall be connected in the manner spedified (b) or (c). Where there are no existing grounding electrodes, the grounding electrode required in part C [250-52] of this article shall be installed". The ONLY exception to the requirement for a grounding rod is a single branch circuit to a seperate building [250-32(a) exception].

The main rule per part C of article 250 requires a grounding rod at every building served by electricity. The specific electrode has to be determined on a case by case basis, and is not required for a single branch circuit installation under the limits of 250-32. In effect, there are only two ways to not have a grounding electrode at a detached garage; a single branch circuit, or no electricity to the building at all. This grounding requirement is vital for both safety and for effective operation of the entire electrical system (beyond the specific property where a detached residential garage is located). This last part is written far better than I could in the 1999 NEC Handbook 250-2 on page 161 and 162. The basic discussion is in the codebook, but the explanatory material is excellent.

I hope that I have answered all concerns adequately, and I hope I don't sound too much like a preacher on a soap-box. I actually learned a thing or two myself by starting this post, so it is a good thing all around!

Good day to all.
 
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Old 01-12-01, 09:13 PM
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  #6  
Old 01-13-01, 07:15 PM
Wgoodrich
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S1nuber

You are quite thorough in your explanation. You are obviously very knowledgeable on this subject. However I have a few points of thought, that differ from your interpretation.

In 250-50 it does say that all [a through d and any made electrodes] must be bonded together to form a grounding electrode system. I am not implying that a grounding system is not required at each building.

However, I will say that this detached garage with a four wire feeder does have a grounding system available, connected, serving, etc. from the main building, by way of the fourth wire in the feeder served from the main building’s grounding system. I will go further to say that when you did install that fourth, wire then you have just created the metal connection of the two buildings by way of the fourth equipment grounding conductor, the same as an existing water pipe etc. would be connecting those buildings. This connection in my opinion makes that panel in the second building a sub panel of the mother building. I will go further to say that the words if available only applies to a ground rod previously installed. The word if available does not in any way require a new ground rod to be installed at that second building. Again you already have a grounding source serving that building by way of the connection of the two buildings from the fourth wire in the feeder that you had installed using the existing grounding source of the mother building.

I believe that you mentioned that you have a handbook. If you would please look up the following commentary provided in the handbook. You should find the words unless one already exists in the commentary found there. These four words should go a long way to support my interpretation concerning this matter of an added ground rod being added to a building that already has an existing grounding system [source] supplied from its mother building by way of the fourth wire.

Handbook 250-32-b-1 illustration

If a single service supplies more than one building, such as illustrated in Figure 250.14, and the feeder is installed with an equipment grounding conductor, Section 250-32(a) requires that a grounding electrode system be established, unless one already exists. [ground rod at mother building, connected by the fourth wire in the feeder to that second building]

I am confused by what you guys are saying. You are adamant about not installing a bonding jumper marrying the neutrals and groundings together in that panel serving the second building if a water pipe or any other metals exist connecting the grounding system of the mother building to the second building because this metal connection between buildings makes that panel in the second building a sub panel. Then you want to install a new grounding source at that second building when you made a more reliable grounding connection between these two buildings by way of the fourth conductor that you installed that runs with the feeder serving that second building from the same mother building, again making that panel in that second building a sub panel.

Don’t make sense to me. If you believe this scenario of adding a new grounding source [ground rod] at that sub panel in the second building that is being fed by a fourth wire run with the feeder, then why don’t you want to install a new grounding source [ground rod] at each sub panel found in the mother building.

The way that I interpret the engineering principles any metal connection including the fourth wire in that feeder makes that panel in the second building a sub panel of the mother building’s service, the same as if that panel in that second building was installed inside the mother building itself. No difference in my mind. I would enjoy your commentary that can possibly show where my interpretation of the engineering principles is flawed.

I am afraid that on this subject we are going to have to agree not to agree.

Wg
 
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Old 01-15-01, 11:24 AM
s1nuber
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Let me ask you a few things WG.

Do you think that 250-50 requires a grounding electrode (I am speaking only about an electrode at this point) at every building served by electricity?

If not, then do you think 250-52 requires a made electrode to be installed at every building served by electricity?

If all of the above answers are no in your opinion, then how do you explain the text in 250-32(a) that specifically requires a grounding electrode to be installed?

How do you explain figure 250.14 (a three wire feeder) and 250.15 (a four wire feeder) that specifically show a grounding electrode installed at each seperate building?
In your scenario, figure 250.15 would be drawn without the blue electrode symbol at building 2.

Do you think that a detached garage is it's own building by the NEC's definition (meaning there would be two buildings on this one piece of property)?

Under your scenario (four wire feeder and no further grounding electrodes or grounding electrode conductors in the detached garage), what would you call the grounding conductor (the uninsulated fourth wire) in the feeder from the main house? Would you call it an equipment grounding conductor, a grounding electrode conductor, or something else?

An answer to each question would help me understand your point of view. Thanks.
 
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Old 01-31-01, 12:42 PM
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I'm posting a reply only to cause this to float to the top.

Juice
 
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Old 01-31-01, 03:17 PM
Antony W. Serio
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Arrggh!!! (spark, fizzle)
Information Overload!
Seriously, if a grounding rod is necessary in both a 3 wire feeder and a four wire feeder, then what is the atvantage of the fourth wire? Currently, there is no grounding rod at my shed, and I do not relish the thought of driving one vertically into the ground. I live on very rocky soil and I seriously doubt if I could drive an 8 foot pipe into the ground without blasting. If the rod could be horizontal (such as a conduit for the wires themselves) it would be a different story.
 
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Old 01-31-01, 07:34 PM
Wgoodrich
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I apologize that I did not see S!NUBER's questions on this subject at the last reply he entered. The main words that should have clearified the differences between opinions are as below copied from the NEC

250-32. Two or More Buildings or Structures Supplied from a Common Service

FROM A COMMON SERVICE.

I take those words to make the fourth wire of the second building to make that second building as one entity with the first building becuase of the fourth wire. EQUIPMENT GROUNDING CONDUCTOR, the same as the fourth wire to a sub panel inside the mother building. The fact that both are fed by a COMMON SERVICE makes this situation different from a stand alone structure requiring a new grounding source. Both buildings are considered as one sharing the same grounding source, same ground rod. The fourth wire is an equipment grounding conductor, not a grounding service conductor.

Wg
 
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Old 02-01-01, 06:14 AM
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Finally getting around to the garage---Here's my scenerio: I have a brand new 200amp service at the house it has three grounding conductors: the original one to the main waterline coming into the house and two additional ground rods drivin just outside house at the time of new installation--all three connected to the nuetral/ground buss in the new 200amp box. I am running 4--#6 wires to the garage(underground) to a 60amp subpanal--approx 20ft to garage(detached). OK--obviously 2-hots, 1-nuetral, 1-ground--the nuetral and ground will be seperate in the 60amp box(unlike the mother box) my question is does the ground from the 60amp box get connected to the ground/nuetral buss in the mother panal or directly to one of the ground rods (previously mentioned) or both? I too do not see need to drive another ground rod--when I have two new ones 20ft away!
 
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Old 02-01-01, 07:23 AM
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Wg was correct, but I feel that a lay person could possibly be unclear. The answer to the second ground rod question is: No, you do not need a second ground rod if you bring your "equipment grounding conductor" (bare ground wire) with you from the main service panel out to the second building. Remember that grounds and neutrals are connected together at the same point in the main panel only, and at any other panel they are required to be connected to completely separate ground and neutral buses. You will have one bus bar for white wires, and a separate bus for your bare wires, and these buses will be electrically isolated from one another. If this is confusing post a reply, this is a topic that has been covered exhaustively, and the correct way to do this is not difficult to explain or to comply with. Good luck.

Juice
 
  #13  
Old 02-01-01, 08:10 AM
s1nuber
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Antony - You can install a ground rod at up to a 45 angle. You could also install the ground rod horizontally if it is covered with 2 1/2 feet of earth. Another option would be a grounding electrode plate, these items are 2' x 2' or so and need to be buried beneath 2 1/2 feet of earth.

Redneck - You should not connect the grounding conductors and nuetral conductors at the panel in your detached garage. You will need two seperate busses. It does not matter how you connect the grounding and nuetral wires in your main service panel as both busses are electrically connected anyway. If you want your detached garage to be wired per NEC standards, you will need to install a ground rod as described in the posts above, even if the existing ones for your home are only 20 feet away.

All - I will try to give you some reasons why each building needs it's own grounding electrode. I don't see how you could reach any other conclusion after reading the text in the NEC, but maybe the why will help.

Let's start with the scenario of a four wire feeder run from an existing service to a detached garage. No grounding electrode is physically installed at the detached garage. The detached garage does have an equipment grounding connection through the main service panel.

Now a bolt of lightning strikes the detached garage, the potential created by the strike sends current along the grounding wire with the feeder to the main panel in order complete it's path to earth. This means that both the main house, as well as the detached garage will likely be shut down.

If you install a grounding elctrode as per the NEC, then there would be a better chance of only the garage shutting down during a lightning strike, as the lightning would take a path to earth at the garage.

Now a different scenario. The earth shifts (earthquake or settling) causing strain on the feeder conductors that causes a ground fault to the panel and severs the grounding conductor. As the grounding conductor is the only path to earth, then the feeder breaker does not trip. All of the metal connected by the circuit grounding wires in the garage are now 'hot'. The only way that the breaker trips is when you go out to the garage and complete the path to ground yourself, and likely die in the process.

Another reason would be voltage stabilization. Every location on Earth has a different potential. 120 volts to ground is not an absolute value, it is a reference value. This means that 120 volts for a house in Miami, FL might actually be 128 volts on an absolute zero scale. If you do not install a grounding electrode physically at the building, then you are changing the zero reference voltage to that of the main house. Depending on a lot of factors, this may affect the way that electrical equipment operates at the garage (especially anything electronic), including circuit breakers and fuses.

My last appeal would be for you to investigate some overhead single phase wiring in your neck of the woods. Find a power utility string with overhead wiring to a smaller subdivision, or rural area. You will likely find a single transformer that may power as many as four residences. Physically go to the pole with the transformer, and you will see a bare grounding wire run to a grounding rod at it's base. Now go to the first distribution pole, and you will find a grounding wire run to a grounding electrode at it's base. If you go to any one of the houses, you will find a grounding electrode installed. Every one of these houses is fed from a common service (the first pole with the transformer), yet every building and pole has it's own grounding electrode.

The entire system is designed and intended to have a grounding electrode at every building or structure served. If you do not install a grounding electrode at every building, then that building will be the weak link, aside from violating the NEC. Keep in mind; weak links have a tendency to break first.

 
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Old 02-01-01, 10:54 AM
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Juice-----yes I realize this is exhaustive--but here we go again you and snuber disagree--he says I need a seperate ground rod---I don't care how I do it I just what it done right the first time! And yes I know the ground and nuetral will be seperate in my garage 60amp box--that was not the question.
Snuber, I like your explaination for the seperate ground rod and will go this route--but if I do this I only need three wires coming from the house--2 hots and nuetral--the ground will go from ground buss in garage box to the new garage ground rod. correct? I do not need to bring the ground from the house!
 
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Old 02-01-01, 11:08 AM
Antony W. Serio
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I was researching wiring my shed in a DIY electric book (Black & Decker) and the book said that I will have to leave the trench for the wiring open until the wiring is inpected. Is that necessary? Also, I have heard both 18" and 24" as proper depth for the feeder line. Which is right?
Finally, if I go with a grounding plate for the shed, will I need to leave the hole that it will be in open as well?
 
  #16  
Old 02-01-01, 11:57 AM
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RED, You will need to leave the trench open, as well as the grounding plate if you need one.

As far as the need for a separate grounding electrode (rod) for the second structure, I still disagree with s1nuber. He and another member, RickM, feel the same way about this. Wg and I do not agree with this. Just as s1nuber maintains that the different potentials at every ground point are different, this same difference will cause current to travel back and forth on the grounding conductor between structures as they continually seek equal potential.

S1nuber quoted 250-50 but neglected to realize that it clearly says "If available on the premises at each building or structure served..." Key words: If available. And the point of this paragraph in the NEC was to say that these [existing] electrodes must be bonded togeher, and not to specify that every building or structure on the premesis needs to have a rod installed if there isn't one already.

Don't get me wrong, s1nuber, I have read many of your posts and can't express enough my respect for you. But this is an interpretation issue, and nowhere in the entire volume of the 1999 NEC have I seen a specific requirement that says clearly and unequivocally you have to put a ground rod at every separate structure on a single premesis that is served with electricityperiod.

Red, I suggest you pick up the phone and call your local code enforcement office. You will have to obtain the name of the department, agency or person who will be inspecting your work. Call them and see what they say for your area. Part of their job is to interpret the NEC, which also means answering your questions so that you can do a correct and safe job. If they say they require a separate rod you have no choice.

Hope that helps. Sorry if I ticked anybody off, but after reviewing the rules and listening to the various opinions on this matter I believe in my current position. Two buildings on the same premisis connected together by a grounding conductor at the main premisis service equipment are considered one building electrically. And I will believe this until the day that someone may convince me otherwise.
 
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Old 02-01-01, 01:06 PM
s1nuber
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Juice and WG -

I just want to state again that it is not important to me who is right, just what is right. I have in no way been offended by anyone's posts or replies on this site. I would also hope that no one else is offended by mine.

That being said, I am very animated by this particular discussion as it involves grounding. Without proper grounding, people die. Grounding is the one area, if done correctly, that allows circuit breakers and fuses to save lives via ground fault protection.

Take a moment to look at the recent 'grouding to water lines' by Mugsy (it was posted on 2/1/01). This person's nuetral was grounded via the connection in the power utility nuetral, at the power pole or pedestal as far as 150 feet away. The distance between that pole ground and the water pipe he connected to was sufficient and different enough to cause current to flow from his panel nuetral back to ground! If this guy had been touching his grounding electrode conductor, and rested his other bare hand on his water pipe, he probably would no longer be with us. A distance of 150 feet or less created enough difference in potential to cause current to flow in enough volume to cause a spark. You are recommending that people install this same kind of situation at their detached garages. The garage panel's level of ground is actually the house's level of ground via the fourth wire, not the level of ground voltage at the garage. This creates a difference in potential between the garage panel and the actual earth the garage sits on. If a difference in potential exists, then current will flow, all it needs is a conductor. That conductor could very easily be a human being.

I would just ask one more thing on this subject. I would like to have the first sentence of 250-52 explained to me. Apparently I do not understand it.
 
  #18  
Old 02-01-01, 01:58 PM
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S1nuber, glad we're still friends. It hadn't ocurred to me that since I'm not offended when disagreed with in an intelligent debate then disagreeing with others shouldn't be offensive. And I absolutely agree that it doesn't matter who's right but what's right.

You may have uncovered something here. 250-50 says IF AVAILABLE at each structure on a premisis the ground rods get bonded together, and 250-52 says if they're NOT available one of the following shall be used (b through d, which lists types acceptable). So in other words, bond 'em together if they're avaiilable, and if they're not available then MAKE 'EM AVAILABLE.

But the key question, to me, is in the word "served". 250-50 says "...each building or structure SERVED...". While Article 100 doesn't have the definition for "served", it says the following for "Service": "The conductors and equipment for delivering electrical energy FROM THE SERVING UTILITY to the wiring system of the premisis served." This leads me to conclude that a building served is one that receives it's electrical energy from the utility. The 1999 NEC Handbook goes on to say that new wording in 1999 makes the clear distinction that if "electric energy is supplied by other than the serving utility, the supplied conductors and equipment could not be considered a service." Therefore, since the detached garage, for example, does not get its electrical energy from the serving utility, it is not a SERVED building. This would leave a detached garage without specific grounding electrode requirements from the NEC.

Curious for responses. Juice
 
  #19  
Old 02-01-01, 04:58 PM
s1nuber
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You have me laughing now, JuiceHead. You and WG are bound and determined to not install ground rods at detached garages, regardless of how many code articles or opinions I throw out there. When I see the phrase 'building served' I believe it to mean served by electricity. I do not think that the word served is a derivative of the word service. Served as used in this context is a verb that I believe to mean supplied with electricity. Service is a noun wich specifically denotes electrical gear powered from a serving utility as you described above. Your thought process is very creative, and if this was a video game, you would have scored mega bonus points. You and WG remind me of a Journeyman I once employed who had similar types of discussions with me regarding code articles. His persistence improved the knowledge of everyone around him, just as you are doing now.

I really was not looking to get into a disection of the english language over this, so let me point the discussion in another direction.

Does your belief that a ground rod is not required stem from an easier installation, or a safer installation? As I have done in earlier posts, I can see numerous situations where not having a ground electrode would be more dangerous than having one. I cannot think of any situations where not having a ground rod would be the safer choice.

Let me know what you think.
 
  #20  
Old 02-02-01, 07:32 AM
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S1nuber, I must say that I am enjoying this conversation also. But it was not my intention to rake the english language over the coals, or to be picayune.

Often in the NEC, as with the law, certain words have very specific implications. Take "shall" for instance. When used in the NEC or in law, it means you MUST and you have no choice. "Shall be permitted to..." in the NEC means you don't HAVE to, but if you do it's OK. In the case of 250-50 & 52, I feel that the NEC has been either vague or confusing, or else they were clear through their usage of their own tech-speak.

Here's an example: When you go to McDonald's you expect service. And after they give it to you and a billion other people they put it right on their sign that says "Over 1 billion served". To receive service is to have been served and I think the NEC meant it that way. I think the intent of 250-50 is to require a ground rod for every service, and that the garage in this discussion is technically not served. Supplied, certainly, but not served and therefore not a service and not required to have an electrode of its own. That's my story and I'm stickin' to it! (Unless something someone says eventually makes me see this issue differently.)

When you cited the case of a number of homes in a development each needing and having a grounding electrode, of course they must, each is served by the utility and has their own service equipment. The electrical energy is supplied by a single source (the transformer), but each home is a completely separate premisis. Key word there, too, premisis. But a home with a detached garage on the same premisis is a single electrical system as I see it.

I suppose ordinarily I would agree that having an extra ground rod couldn't hurt, it's more than what's required. The NEC requires one rod for a service, but my utility requires two. So when I upgraded my own service last year I installed two, and exceeded NEC spacing requirements by placing them exactly 7 feet apart. Also along those lines, I use #12 wire in my home as a minimum, even on 15 amp circuits, even though the NEC permits #14. So ordinarily if there's any question I go with more and rarely go with the minimum. And I seldom design anything based on what I can "get away with". However...

I believe it was Wg that explained the concept of "seeking", where the different potentials of each electrode, bonded together with the others, the grounding electrode conductor would act to carry current back and forth between them, continually trying to achieve equilibrium. And it is this that concerns me. I think otherwise I wouldn't advise people not to do the garage ground rod, but instead I may otherwise only say they could if they wanted but didn't actually have to.

See where I'm coming from? What are your thoughts on potential seeking between the electrodes? I know 250 says that all electrodes in a system must be bonded together, so there's another conflict in my mind. I don't believe the NEC would require something that could be hazardous, and if using an appropriately sized grounding electrode conductor all points of the system would be electrically the same exact potential.

Sure would be easier if the God of Electricity would descend from on high and issue a "Thou shalt" or "thou shalt not" put a ground rod out at you garage, and be done with it!

Later,

Juice

[Edited by JuiceHead on 02-02-01 at 09:38]
 
  #21  
Old 02-02-01, 08:19 AM
Antony W. Serio
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Earlier in this post, it was mentioned that there can be no conductors other than the feeder line between the two structures. Does that mean that the wires have to go through a non-conducting conduit, such as PVC?
Also, if I want a phone out in my shed, does that mean that the phone line has to be in a seperate trench or conduit? Finally, it was mentioned that a horizontal grounding rod could be used. Could a metalic conduit be used as a grounding rod? If so I won't have to dig a second trench or a hole for a grounding plate.
If the feeder line can not go through a metalic conduit, could I have a horizontal grounding rod share the trench and parallel the (non-metalic) conduit? In other words, is there a minimum distance between a horizontal grounding rod and a utility line?
 
  #22  
Old 02-03-01, 06:35 AM
s1nuber
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Antony - I would run your feeder in pvc conduit. Run a four wire feeder in this conduit (60 amps minimum or #6 copper THHN). This conduit will need to be in a trench with 18" of coverage, so a 20" deep trench will be needed. You can install a phone cable in the same trench, it will need to be one foot above pvc conduit, and 6" below grade. If you deepen your trench to 2 1/2 feet at the garage end, you can lay in a horizontal ground rod.

If you use metal conduit, you cannot run a three wire feeder.

If you use metal conduit, you cannot install the ground rod in the same trench.

If you run a phone line, you cannot install a three wire feeder.

Metal conduit that encloses the circuit may not be used as a grounding electrode.

Hope that answers your questions, enjoy your day!
 
  #23  
Old 02-03-01, 08:00 AM
s1nuber
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Juice -

We must have fundamental differences about electrical theory and how electricity works. Your seeking potentials is a reason for you to not install a ground rod, where I believe it is a reason to install a ground rod (aside from the NEC requirement).

Maybe if you thought of a ground rod at the garage as 'bonding' the earth to the equipment ground in the feeder. It's purpose in this context is to ensure there is no difference in potential between the grounding conductor and the earth at the garage. If there is no potential, then current will not flow between the earth and the grounding conductor. If you do not install the ground rod, then every time someone touches both the ground (the physical earth) at the garage, and any equipment grounding conductor in the garage, they will be causing current to flow. Causing uncontrolled currents to flow is exactly what we as electricians are in existence to prevent.

I do concede that if 250-52 were to be reworded, it would make my side of the argument clearer. However, 250-32 (a) refers to part C of article 250 as requiring a grounding electrode, and gives specific guidelines how to connect it when two or more buildings are supplied by a common service.

So here is a question for you. The interpretation of the code to need a grounding rod at a detached garage is supported by the following:

interpretation of 250-50 (does served mean service equipment, or electricity in general?)

250-52 does not specifically say at every building, just refers back to 250-50 with the above problem.

250-32 (a) clearly states "the grounding electrode REQUIRED in part C of this article", and gives guidelines on how to connect it. It then goes on to specifically say "Where there are no existing grounding electrodes, the grounding electrode(s) required in part C of this article shall be installed.".

The word shall is used in all of the above articles.

Article 100 definition of building (two entirely seperate buildings are involved by definition)

The arguement against a grounding electrode has nothing but interpretations and opinions to support it, no code article can be referenced that supports a lack of a ground electrode. This arguement hinges exclusively on the use of the word served, where the arguement for has almost four pages of code dedicated to grounding electrodes in different situations.

Another question, why does 250-32 (a) have an exception that does not require a grounding electrode? Exceptions are the rarity (Webster's definition - exception 2. that which is excepted, excluded, or separated from others in a general description; the person or thing specified as distinct or not included; a case to which a rule, general principle, etc. does not apply), and if not having a grounding electrode is the rarity, then what must be the common practice?

The argument for has two pictures in the 1999 NEC handbook that show a ground electrode required at each building for two seperate buildings supplied by a common service (250.14 and 250.15), where the argument against has only one picture (250.13) which is labeled as the exception (for single branch circuit installation only).

I see the side of the arguement to believe that only one grounding electrode system is required for each service, but this arguement does not have any code articles to support it. The evidence is overwhelmingly in favor of a grounding electrode at each building, even if only one word may be interpreted differently.

Everything that I have just posted, I posted earlier, so I do not think that you will be swayed. You had mentioned a higher power, so I would like to take this discussion to one of the trade publications, and get an interpretaion from one of their code experts. Is there a trade magazine that you subscribe to that we could ask for guidance from?
I know that CEE news, Electrical Contractor, and EC&M all have code forums. Maybe we should send to all three, and increase our chances of being published?

Let me know what you think. Enjoy your day!


 
  #24  
Old 02-03-01, 08:03 AM
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This subject strains the brain... I'm just a layman but I think I understand where you guys are disagreeing, it's interpretation. I think the confusion is over the terms "grounding system" and "grounding electrode". A grounding system would be (for example) your service entrance. There's a ground at the pole, and at your panel the ground is connected to water pipe and a grounding electrode. This creates a grounding "system" not just an electrode. The same applies to a separate building, if you run a grounding wire from your service, then the building would be grounded, but it would not have a grounding system. I read the code as requiring this "grounding system" rather than simply using an electrode. So to sum it up, even if you run a separate grounding wire from your main panel to the garage, the grounding wire must be bonded to metallic underground water piping and a grounding electrode. Also, the code says (I believe) that this grounding electrode will be used where available. This is where confusion sets in, because what they don't tell you is that where it's not available, you're gonna make it available! If I'm way off, forgive me. Like I said, I'm a layman. I'm just trying to get a handle on this.
 
  #25  
Old 02-03-01, 09:14 AM
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picayune

..you guys are keeping me awake

yawning...did someone say 'picayune' ? If you make me get the dictionary out, I will stop following this thread!

I am only following this thread because I built a shed and did not put in a ground rod, and I am waiting for a 'yes' or 'no'. Sheeez

Yes,yes, take this simple question to a higher authority. I can't wait to see 3 more expert professional opinions in this thread !!

I have an outdoor, stand-alone, duplex, weatherproof outlet 80 ft away from my 'served' shed, for my compost bin and shredder motor. Nicely done, buried conduit, permanent installation, concrete pad, no shortcuts. I wonder if I need a grounding rod for it, since my compost bin is now a 'served' structure (or is it).

Seriously, keep up the good work! Most importantly, I like the clarity with which everyone writes. It really helps the reader with the task of comprehending.
 
  #26  
Old 02-03-01, 10:00 AM
Wgoodrich
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S1NUBER

Your scenerio involving utility poles and a new grounding source [copper pie under the pole] is required at each utility pole because they are each considered a stand alone structure. What you overlooked is that between each of those poles that you discribed only have three conductors between each of those you discribed. No fourth wire is present only two hots and a neutral.

To All

You are allowed to install the ground rod [made electrode] at that second building being served by a common service and by a common grounding system ONLY IF THE FOURTH EQUIPEMENT GROUNDING CONDUCTOR RUN WITH YOUR FEEDER IS SIZED EQUAL TO THE MINIMUM GROUNDING ELECTRODE CONDUCTOR. A maximum size required grounding electrode conductor for a made electrode is #6 copper. That fourth wire [equipment grounding conductor because it is found from the load side of the service in the main building carrying the grounding system of the main building to the second building] must be #6 copper of larger. This fourth wire [equipment grounding conductor] becomes a grounding electrode conductor because all grounding sources [ground rod, metal water pipe, etc.] must be bonded together to make the grounding system. You would be considered within the Code in adding a ground rod at the second building only if that fourth wire found running with the feeders to that second building is #6 copper or larger and connected at the main service of each building because that fourth wire is now considered a grounding electrode conductor and that grounding electrode conductor must be bonded to the grounding system of the main building to become a part of one grounding system. Otherwise the difference of potential is available causing a hazard.

The earth or a fourth wire run with feeder that is smaller than the required #6 copper grounding service conductor required for a made electrode, is not allowed to be a method of making all grounding sources to be bonded together in the same grounding system. When you install that fourth wire or metal path [water pipe ect.] you carried one grounding system to a second grounding system.

S1NUBER

Your grounding source at the second building requirement is fulfilled by carrying the grounding system to the second building by way of the fourth wire in the feeder between buildings, thus making both buildings as one building due to the common service and the common grounding source.

If you add a supplemental ground rod at that second building that is connected by a common grounding system shared with the main building, then you must ensure your fourth wire is #6 copper or larger and is connected at the main panel in the main building not from a sub panel in that main building, thus bonding all grounding sources as one grounding system.

Your statement saying that two grounding sources are not forbidden by the NEC is true, but a second grounding system is only allowed if you have a transformer creating a separately derived system that is not in contact to the primary side of that transformer, or you have a minimum of a 2 hour fire wall separating that building into to separate buildings.

To all

I feel that we will never be convinced which interpretation is correct even using magizine publications.

However this CAN be resolved. I suggest that someone copy this whole string and send it to the NFPA with a form requesting a formal interpretation from the NEC itself. This form is found in the NEC with instructions as to how to request that fromal interpretation.

We may never agree on an interpretation on this subject. But we sure have taken a tour of ARTICLE 250 in the NEC!

Good knowledge found in this string, but everyone is going to have to make there on dicision on the subject.

Wg
 
  #27  
Old 02-03-01, 01:11 PM
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Lugnut, what you described is a single outlet with a receptacle. According to the definition of "branch circuit" in Article 100, and verbage in 250-32, you are thereby exempt from a ground rod!

S1nuber, I may have been unclear. The seeking I am talking about is between the potential of the service grounding electrode and the garage grounding electrode, not the potential difference between a garage and its theoretical electrode. Of course there is a difference between a building and 8' of earth, or rods never would have been invented! Even though 250-32 wants them bonded together on the same premisis, the two ELECTRODES at 2 different locations will have 2 different potentials and the electrode conductor which bonds them could be carrying current back and forth between the ever changing potentials of electrodes located far apart.

250-32 does say "shall", as required by part C. It's part C that has the word "served" which I also wish would be clarified.

"Not required" in the exception (which you so thoroughly defined) does indicate one branch circuit, which clearly does not apply in our discussion and CAN'T be cited as an arguement for no electrode for the garage by definition of branch circuit in Article 100. The post "grounding outlet in garage", where the gentleman has one receptacle circuit and no sub-panel hung off one breaker in his main panel in the house, is what the exception addresses.

Given the bonding requirements of 250-32, I have been thinking this over and over and can't believe that you SHOULD NOT have a rod at the 2nd building, and came to the conclusion that all points on a grounding electrode system absolutely must be of the same potential or NEC wouldn't require bonding of electrodes to form a single grounding electrode system, and that the whole point is to have one single potential that is ground, or earth, itself, everywhere on a single electrical system. NOW, Wg has clarified and reinforced my conclusion by citing that if a #6 or larger copper conductor is used you will have sufficient wire area to make "travel" of seeking current moot. In such a large conductor, current of the amounts anticipated for the variations in potential between two points in the earth only as far apart as a garage and a house on the same premisis should be should be transmitted instantaneously.

I have always had success in explaining electrical current to lay people in terms of plumbing. To make my last point clearer, imagine trying to transfer a gallon of water from one vessel to second vessel located 20 feet away using 1/8" tubing. (Liken that to small gage wire.) Water will be traveling between the two vessels for awhile but will get there eventually. But in the mean time there is a difference in potential between the volume of both vessels. Liken that to electrical potential. If you poke a hole in the 1/8" tubing while volume in each vessel is different, there will be a leak. (Liken this to an electrical shock!) That's the potential difference leaking out, and if that were electricity the poking of that hole is equated to touching a bare metallic grounded surface by a person when there are differing potentials. Poe a hole in the tubing when empty and you get nothing.
OK, now imagine installing 2" pipe between the two vessels. Potential will instantly reach equilibrium between the vessels. No "seeking", if you follow me.

So Wg has clarified this for me: If a grounding electrode conductor of sufficient size is bonded to two electrodes, the potential of one is instantaneously equalized with the other without delay, and therefore there isn't any practical traveling current present between the two points.

I know this was kind of long-winded and I apologize. I'm talking myself through an understanding of this issue at your expense, but also for the benefit of anyone interested enough to want an understanding of what is the right thing in the end who may not have a pre-disposed opinion, as many of us do.

Long & short: there is still some question in my mind as to the REQUIREMENT, but I have had my opinion modified from "shouldn't" have the garage rod to "can, but not required" under the circumstances we have discussed here. Until such time as "served" is clarified, I still do not believe that a rod is required in the garage if you bring your equipment grounding conductor with your feeders from the main panel to the garage.

Whewww! Could anyone have imagined that the discussions in a DIY community forum would become so philisophical, and ever take on the appearance of a 42 page supreme court interpretation of law??? It has been truly both taxing and enthralling discussion and I thank you all for the wisdom shared and opinions expressed.

Oh, and can you believe I resurected this post from somewhere around page 13 of the long forgotten post archives just so that Antony could wire his garage? Started this whole thing up again just when we al thought it was safe to go in the water!

Exhausted, Juice
 
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