Prove my dad wrong!

Reply

  #1  
Old 10-05-09, 09:47 AM
D
Member
Thread Starter
Join Date: Jun 2009
Location: Illinois
Posts: 6
Received 0 Votes on 0 Posts
Prove my dad wrong!

My dad and I were discussing the need for a ground on a sub panel I'm installing in my detached garage. Here is the scenario (it's not that complicated):

I have my main service panel in my house. I'm attaching a 60 amp breaker in it and running a feeder to a sub panel in my detached garage. Our "discussion" has been centered on the need to run 4 wires (2h, 1n, 1g) or 3 wires (2h, 1n).

From what I've read online, the NEC way would be to run 4 wires and separate the neutral and ground buses on the subpanel. That was the approach I was planning on taking.

My dad insists that running the ground to the sub panel and having separate neutral/ground buses makes no sense since they both converge in the main anyway. Could someone help me understand why the 4 wire approach (with separate sub panel neutral/ground buses) is better or safer than the 3 wire (shared sub panel neutral/ground bus) approach?

BTW, I have read the great sticky sub panel post (http://forum.doityourself.com/electr...-drawings.html), I just want an answer to the why question.
 
Sponsored Links
  #2  
Old 10-05-09, 10:05 AM
L
Member
Join Date: Oct 2009
Location: Maine
Posts: 13
Received 0 Votes on 0 Posts
I'm going to be eagerly awaiting the answer to this too. I'm actually just finishing up with almost the same project. I am not an expert, or in any way qualified, but my research led me to the exact same conclusion that you came to about running 4 wires and keeping the neutral and grounds separate in the sub panel.

A couple of other things I found were that if the wires from the main to the sub panel are individual cables, they must be in conduit the entire length of the run. in my case that's about 75' in my basement and 100' underground to the garage. Also, two new grounding rods are needed for the garage. I'm sure you already found these things out too, since you did some research.

Hopefully someone has some good answers to the theory behind the separate ground and neutral in the sub panel, even when they are bonded together in the main panel. I haven't been able to fully understand it either.
 
  #3  
Old 10-05-09, 10:22 AM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,163
Received 1 Vote on 1 Post
Originally Posted by daytonkilgus View Post

My dad insists that running the ground to the sub panel and having separate neutral/ground buses makes no sense since they both converge in the main anyway. Could someone help me understand why the 4 wire approach (with separate sub panel neutral/ground buses) is better or safer than the 3 wire (shared sub panel neutral/ground bus) approach?
.
well, he is correct that they do connect at the main panel but the do not at the sub panel. Why? well, a neutral is a current carrying conductor and if you only use a 3 wire feed (btw; not legal per 08 code anymore) you do not have a GROUND wire. You have 2 hots and a neutral. All 3 are current carrying wires. So (and this is one reason 08 code changed from the old 3 wire system) if you have ANY other metallic connections between the garage and the house, that path may become part of the neutral circuit and carry current as well. Not a good thing for whatever it is attached to but more importantly, if interrupted, it could present a hazardous condition, just like opening any other neutral is.

So, not only is it current code requirement to run a 4 wire feeder, it is also safer.

btw: you do need an grounding electrode system at the detached building that is connected to the grounding system in the subpanel.

AND; if the garage is new, you need to use the steel in the foundation for a grounding electrode by attaching a GEC (grounding electrode conductor) to the rebar in the concrete and to the panel ground bar.
 
  #4  
Old 10-05-09, 10:24 AM
P
Member
Join Date: Feb 2002
Location: port chester n y
Posts: 2,117
Received 0 Votes on 0 Posts
The Code requires that the Neutral be isolated from Ground at any point beyond the Service dis-connecting means. If the Neutral was Ground-connected at some point beyond the Service dis-connect , for example at the sub-panel, there would be two parallel paths for Neutral current flow between the sub-panel and the Service, one path the Neutral and the other the Grounding conductor , because the Neutral and Grounding Conductors are connected together both in the Service panel and in the sub-panel.
The Code requires a Grounding Electrode at the detached structure.
 
  #5  
Old 10-05-09, 11:03 AM
D
Member
Thread Starter
Join Date: Jun 2009
Location: Illinois
Posts: 6
Received 0 Votes on 0 Posts
Let's assume I take the 4 wire approach: Code aside, why do I need separate grounding rods at my garage?

Thanks for satisfying my curiosity.

nap, the garage is existing, not new.
 
  #6  
Old 10-05-09, 11:20 AM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,495
Received 35 Votes on 27 Posts
I've posted this link before and maybe it's time to make it a "sticky". The concepts of bonding and grounding are complex and cannot be answered in just a couple of paragraphs.

This is a twelve part article but it is the best explanation that I have ever seen on the subject. It is written simply enough that most people can grasp the concepts without having a degree in electrical engineering.

Grounding vs. Bonding
 
  #7  
Old 10-05-09, 11:38 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 43 Votes on 41 Posts
Originally Posted by daytonkilgus View Post
Let's assume I take the 4 wire approach
I'm sure your dad's experience was from a time when three wire feeders were legal and common; however their use has been restricted in the last few code revisions.

As of the 2008 National Electric Code, a four wire feeder is the only legal option. Previous editions allowed a three wire feeder under specific circumstances, but all of those exceptions have been removed.

The primary motivation for this is that in a three wire system, damage to the neutral wire can result in a shock hazard on exposed metal surfaces in the outbuilding. This problem has become apparent over time as neutral wires tend to corrode after years or decades in service.

why do I need separate grounding rods at my garage?
Grounding electrodes provide several functions such as lightning protection, reference grounding, and corrosion protection. There is really a lot of science and engineering theory behind earth grounding that's too complex to get into here, but suffice to say that it is required by every electrical code, power company and engineering specification that I'm aware of.

The fundamental confusion here is that the equipment ground, which is the fourth wire in the feeder, serves an entirely different purpose than the grounding electrode, which connects the electrical system to the earth. To the layman they are both called "ground" when really they're completely different systems both with important functions.

==> furd, thanks for posting that link.
 
  #8  
Old 10-05-09, 03:12 PM
B
Member
Join Date: Aug 2008
Location: Kansas
Posts: 233
Received 0 Votes on 0 Posts
Since I have some time today and the sticky drawings are mine it would seem appropriate that I respond to your question about 3 wire feeders and 4 wire feeders to sub-panels. And why the the neutral and ground are bonded at the service equipment and why they are not bonded at sub-panels being served with 4 wire feeders. Also why are they bonded in sub-panels with 3 wire feeders as your Dad likes to do.

I'm going to attach some drawings of mine for you to help answer the questions you ask. This first one is a drawing showing the effective ground fault path that is required to open a circuit breaker in the event of a fault.
First thing to understand as you look at the drawing is that all current be it system current from the operation of devices and appliances in the home or fault currents from wiring mishaps will always seek their source. That source is the serving transformer to the dwelling and structures on the premises.
The next thing to understand is that current seeks all paths available to it to return to the source transformer. However if given a single extremely low impedance/resistance path back to the transformer current will flow on that path disproportionately or nearly 100% rather than use a high impedance or resistance path. In residential systems there are generally 2 paths to be concerned with... that being the system wiring from the transformer to the dwelling and other buildings served and then you have earth/dirt. You can see this in the drawing.
You will notice that both the branch circuit neutrals and the equipment ground wires become bonded at the service equipment where the main disconnect is located.
Why? Look closely... there is only 1 low impedance/resistance path back to the transformer center tap (Xo) at the "MAIN" panel and that is the service grounded conductor called in most cases your 'service neutral'. The other path is through earth (high resistance) to the transformer ground rod where the transformer center tap has been intentionally grounded to earth. Therefore nearly all current neutral or fault will take the service neutral to the source.
It is important to note that if we break or open the service neutral the only path left is the earth path which is high resistance and your circuit breakers will not trip if a fault exists because earth will not allow enough current to flow to the source and consequently thru the circuit breaker to open or trip it to clear the fault.



So the key here as to your question is... there is one path to the source for neutral and fault current at the service equipment (main disconnect panel) ... that is low resistance... that being the service neutral. Therefore neutral and equipment ground bond here so that both fault and neutral current can utilize the service neutral as the path to the transformer (source).

Now to separate 3 wire vs 4 wire feeders to sub-panels. First thing to note is that 3 wire feeders are only allowed to detached structures from the service equipment and only if you do not have any other metallic paths like metal water lines or coax or phone lines that are or can become part of the system configuration thru grounding requirements or faults.
And as previously mentioned if your jurisdiction is using the 2008 NEC then 3 wire feeders are not allowed. But why? Looking at the next drawing of a 3 wire feeder to a sub-panel from the service equipment notice that you are required to bond the neutral and ground at the sub-panel. This is because in this case the feeder neutral is playing double duty both as the path for neutral current to flow to the service panel and then to the transformer under normal operating conditions and it is also playing the path for fault current to return to the transformer. Essentially the same as what is happening at the service equipment. We install the jumper shown to bond the metal of the sub-panel to this same path in the event of a fault to the metal from a hot conductor. There are a few safety issues with this configuration vs separating ground and neutral as we do in 4 wire feeders. The biggest is in the event of an open neutral or damage to the neutral in the feeder as ippooks described. This interrupts the only path that is low resistance back to the source and if a ground fault exists from the event that opened the neutral or an event that comes later then all metal that is in the fault path including the metal of the sub-panel will come to line voltage and your breaker will not be able to clear the fault. An open neutral is going to be immediately noticed even though you may not know the reason. This is because you will not be able to operate 120 volt loads such as lights and several other issues will result from this kind of fault. The first place you are going to go if your not thinking is the sub-panel and your going to touch the metal of the panel as you open the access door to the breakers. Not knowing that the metal of the panel is energized at line voltage......ouch!! If a ground fault does not exist you need to be very careful to not become the path for neutral current by getting in series with it at the fault point. You need to remove system voltage at the breaker in the service equipment that is protecting the feeder conductors before touching or messing with the sub-panel.



Now 4 wire feeders neutral and ground not bonded. biggest difference is what was mentioned by Pattbaa and nap....if you bond the neutral and ground in the sub panel you will create equal low resistance/impedance paths and neutral current under normal operation will split evenly on both the feeder neutral and feeder equipment ground. You never want the equipment ground to carry neutral current where it is unexpected. This objectionable current due to the parallel paths created has been fatal to many homeowners and electricians.
Also note that if we open the neutral in this configuration of an improper neutral to ground bond the equipment ground will now carry ALL the neutral current of the system even though the neutral has been opened. This would be totally unexpected as you would not know that you have an open neutral due to the equipment ground carrying the neutral current.



Hope all this helped....
 
  #9  
Old 10-05-09, 03:30 PM
B
Member
Join Date: Aug 2008
Location: Kansas
Posts: 233
Received 0 Votes on 0 Posts
Just so you can see an actual improper neutral to ground bond at a sub-panel I'll post these pictures. Both show neutral to ground bonds with 4 wire feeders. Neutral current is flowing on the equipment ground in both sub-panels. Other issues exist in these panels but focus on this bonding of neutral to groundusing a 4 wire feeder.



 
  #10  
Old 10-05-09, 06:10 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 15,144
Received 84 Votes on 72 Posts
Thanks for stopping by Bruto. Hope this didn't take too much time away from your fishing .
 
  #11  
Old 10-05-09, 07:13 PM
B
Member
Join Date: Aug 2008
Location: Kansas
Posts: 233
Received 0 Votes on 0 Posts
Originally Posted by pcboss View Post
Thanks for stopping by Bruto. Hope this didn't take too much time away from your fishing .
Hi PCBoss

One of the things I am very concerned about is that DIYer's understand this 3 wire vs 4 wire feeders to sub panels. I see it done incorrectly way too often.

As for fishing... I just returned from a week trip and will be leaving again in a few days.

Wife said I spend too much time on the internet and need to go back to work or go fishing. I chose fishing.....
 
  #12  
Old 10-06-09, 08:08 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 43 Votes on 41 Posts
Sounds like an easy choice to me.
 
  #13  
Old 10-06-09, 08:19 AM
B
Member
Join Date: Oct 2008
Posts: 1,312
Received 0 Votes on 0 Posts
Short answer: It is for the same reason there is a separate ground wire run to each outlet!
 
  #14  
Old 10-07-09, 08:05 AM
I
Member
Join Date: Jan 2008
Location: Texas
Posts: 123
Received 0 Votes on 0 Posts
Add me to the list of confused.

About a year ago, I started this thread asking how neutrals, grounds, ground rods, et al, should be set up in my electrical system which contains a genset ATS (which is also the service entrance/disconnect) and three subpanels, two of which are "feed-thru" to the next one on the line. The responses said that the neutrals and grounds should be "independent" all the way back to the ATS, i.e., a four-wire non-bonded neutral setup. That's what I now have. However, when I asked about the multiple ground rod connections that existed at that time, the response was that I should have only one ground rod and only the ATS ground should be directly connected to it.

So what I have now is a four wire system from my home subpanel all the way back to the ATS. All neutral bars in the subpanels are floating. the neutral bar in the ATS is bonded to the box. The only connection to the ground rod is from the ground bar in the ATS.

Is the above an incorrect setup? Should I have more ground rods, or more connections to the ground rod? Do I need to add a ground rod at the house and tie it into the ground wire where it leaves the house on its way back to the shop?

Thanks,
Ira
 
  #15  
Old 10-07-09, 03:36 PM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,163
Received 1 Vote on 1 Post
just quickly reading your situation but the separated neuts and grounds is still correct. If all the panels are in one building, you would only have one Grounding electrode system. You would have another one only if you went to separate buildings.
the ground and neut should only be tied together at the main service disconnect. The grounds in the other panels acre connected to the GE system by virtue of the egc (equi0pment grounding conductor).

in other words, it sounds like things are correct in your installation.

with the only exception of what is tied to the grounding electrode:

main disconnect, water pipe, (if new) rebar in the foundation, and anything else the code lists.
 
  #16  
Old 10-07-09, 04:32 PM
I
Member
Join Date: Jan 2008
Location: Texas
Posts: 123
Received 0 Votes on 0 Posts
in other words, it sounds like things are correct in your installation.

with the only exception of what is tied to the grounding electrode:

main disconnect, water pipe, (if new) rebar in the foundation, and anything else the code lists.
They are separate buildings. My POCO meter, ATS, and the first two load centers (subpanels) are all in my "shop". The third load center (subpanel) is in my home 150' away. The four wires go underground from the second subpanel in my shop to my home.

Not sure what you mean by your last two sentences, but the 8' ground rod is located within a few feet of the ATS and meter. The only thing connected to it is a ground wire that goes back to the ground bar in the ATS.

So the only real difference between my setup and the OP is that my service goes to my shop (garage) first, then to the house, whereas the OP's goes to the house first then to the garage. Why does he need a ground rod at the shop, but I don't need one at the house. Both of us have four wires "going back".

Sorry if I'm confusing this even more, but I'm really trying to get this set up correctly. The house was originally built 20 years ago, including the shop with the utility entrance location and the first two subpanels. The ATS was added (and the first subpanel changed from the service disconnect behind the meter to a subpanel next from the ATS) about a year ago. One other thing just to be clear, the ATS does not have any breakers in it other than the main service disconnect and the genset breaker. In other words, it is a "whole house ATS".

Aplogies to the OP for temporarily hijacking his thread, but at least it's basically the same subject.

Thanks,
Ira
 
  #17  
Old 10-07-09, 05:17 PM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,163
Received 1 Vote on 1 Post
Ok, since you have said these are seperate buildings, it is wrong. You need a grounding electrode system at each building.

Please tell me the feed through panels do have main breakers in them though and they are not MLO panels, well, just the ones in any separate building anyway.
 
  #18  
Old 10-07-09, 06:38 PM
B
Member
Join Date: Aug 2008
Location: Kansas
Posts: 233
Received 0 Votes on 0 Posts
I should be fishing.....

Just to get ourselves on solid ground is this what you have.....



Some questions...

1.) How many poles is the transfer switch ?? In other words does it switch the neutral from utility to generator or does it have a neutral bar and the neutral is not switched between generator neutral and utility neutral ?

2.) The 2 feed thru panels are Mobile Home panels ? If so they should already be set up for 4 wire feeds with neutral and ground separate I would think.

3.) Are all the panels and ATS 200 amp panels ? The 2 in the shop are 200's with main breakers according to your link. So Is the house panel also 200 amp with a main breaker. This is what nap is asking....

4.) What size conductors (cu or al) serve these 3 panels ?

5.) From the ATS does panel 1 and panel 2 have 4 wire feeders. You said the underground to the house panel was 4 wires.

6.) What generator do you have?
 
  #19  
Old 10-07-09, 08:32 PM
I
Member
Join Date: Jan 2008
Location: Texas
Posts: 123
Received 0 Votes on 0 Posts
Originally Posted by Bruto View Post
I should be fishing.....

Just to get ourselves on solid ground is this what you have.....



Some questions...

1.) How many poles is the transfer switch ?? In other words does it switch the neutral from utility to generator or does it have a neutral bar and the neutral is not switched between generator neutral and utility neutral ?

2.) The 2 feed thru panels are Mobile Home panels ? If so they should already be set up for 4 wire feeds with neutral and ground separate I would think.

3.) Are all the panels and ATS 200 amp panels ? The 2 in the shop are 200's with main breakers according to your link. So Is the house panel also 200 amp with a main breaker. This is what nap is asking....

4.) What size conductors (cu or al) serve these 3 panels ?

5.) From the ATS does panel 1 and panel 2 have 4 wire feeders. You said the underground to the house panel was 4 wires.

6.) What generator do you have?
Your diagram is exactly right.

1. The ATS does not switch neutral. It only switches the two hots. There is a ground bar and a neutral bar in the ATS. The ground bar is always bonded to the enclosure. The neutral bar can float, but it is currently grounded to the enclosure via a bonding strap/lug.

2. Everything downstream from the ATS is four wire. So it's four wires from the ATS all the way to the last subpanel in the house. The two subpanels in the shop are 200A mobile home panels (Seimens W0816L1200CT with feed thru lugs and 200A main breakers). They do have separate neutral and ground bars. The neutral bonding screw is backed out (not bonded) in both.

3. Yes...all the panels and ATS have 200A breakers. There is actually a 100A breaker in the genset enclosure, but the genset line leads go into a 200A breaker in the ATS. The service entrance breaker in the ATS is 200A.

4. I thing the hots and neutrals are 2/0, but I don't remember for sure. They are the same size. Not sure what the ground is, but it is smaller. That's for all wires from the meter box to the house subpanel. Also, all are copper. No aluminum downstream of the meter. Also have 2/0 copper from the genset to the ATS (about a twenty-foot run).

5. Downstream from the ATS (including to the first subpanel from the ATS), everything is four wire, all neutrals floating, all neutral and ground circuit wires attached to their respective buss bars in the subpanels. In other words, for each branch circuit in a subpanel, the neutral goes to the floating neutral bar and the ground goes to the bonded ground bar.

6. The genset is a Guardian/Generac 5638 liquid cooled, 1800 rpm, 22kW (39kW surge), LPG fueled, 2.4L Mitsubishi 4-cyl. Generac has recently rebranded its Guardian gensets to Generac models, so the exact same genset is now called a Generac QT022. Mine is just over one year old. The ATS is a Guardian/Generac RTSE200 (service entrance rated). It all worked great during the four days after hurricane Ike that we were without power. Everything worked exactly as if we had POCO power.

It probably doesn't matter for this discussion, but subpanel 2 in your drawing does not have any breakers other than the main. It's only purpose is to be able to shut off power to the house without killing power to the shop. There are only about five circuits in the shop subpanel (subpanel 1), the most important being for my 1.5hp water well pump that provides water to the house. The well is close to my shop, so that's why it is wired in to that panel. No other "big" circuits in the shop, i.e., the rest are all regular 20A circuits.

Hope all that makes sense.

Thanks,
Ira
 
  #20  
Old 10-07-09, 09:59 PM
B
Member
Join Date: Aug 2008
Location: Kansas
Posts: 233
Received 0 Votes on 0 Posts
Thank You for the detailed reply to all questions.


You have a typical standby generator with neutral and ground not bonded at the generator. Neutral is not switched at the ATS. Therefore you do not have a separately derived system needing its own ground reference. The generator does not need and should not have a ground rod since the generator neutral is solidly connected thru the ATS to the system or utility neutral and grounding electrodes. The ATS is your service equipment so your electrode grounding conductors should terminate in the ATS at the grounding bar. This would mean 2 ground rods and any existing electrodes like metal water pipe or rebar (UFER). The neutral in the ATS should be bonded to ground and the enclosure. I believe you say it is..so your good.

Your panels in the shop are also good.. as are the feeder conductor sizes if they are 2/0 copper. All panels except the ATS need neutral and ground separated. NO other grounding is required at panel 1 and 2 (no ground rods) other than the feeder equipment grounding conductors and branch circuits.

At the house the main breaker satisfies your dwelling disconnect. However you need a grounding electrode system for the house. Probably 2 ground rods will be fine.

Lastly the generator is required to have a disconnect. You have that in the form of a 100 amp breaker in the generator control panel I believe so your good to go.
 

Last edited by Bruto; 10-07-09 at 10:31 PM.
  #21  
Old 10-08-09, 12:52 AM
I
Member
Join Date: Jan 2008
Location: Texas
Posts: 123
Received 0 Votes on 0 Posts
Bruto...thanks for the explanations. They've been very helpful. As I've mentioned in a previous thread, I've had a tough time finding an electrician around here that understands these concepts/requirements, which I find pretty alarming. Two different "master" electricians (on completely different occasions within the last three years) insisted on bonding the neutrals to the enclosures and/or grounds in the two subpanels in the shop. I live outside the city limits, and the county doesn't do electrical inspections, so I don't have an inspector to approve the work.

I went back and read the sticky thread which also helped a lot. But I do have a few more questions. Again, apologies to the OP, but the answers may help him, too. To be clear, all my pipes are PVC, so I don't have any ground wires connected to water pipes. Nor do I have a foundation grounding system on either building.

1. My home's subpanel is actually on an inside wall. The four wires from the 2nd shop subpanel come out of the ground at the house next to an outside wall. There is a junction box mounted on the outside wall. From the junction box, the wires go into the wall cavity, up to the attic, over about twenty feet then down in the inside wall cavity that contains the home's subpanel to the subpanel main breaker. In the junction box on the outside wall, the hots and neutral are connected to insulated lugs. The ground is connected to a lug that is not insulated, i.e., the junction box and ground wire are bonded. So in order to add a ground rod, can I simply add another lug to the junction box similar to the lug the ground wire is connected to, and run a wire from that lug to the ground rod? Or do I need to have a some kind of "three way" lug? What gauge does that ground wire need to be?

2. I understand that the two subpanels in the shop don't need to be directly connected to any ground rods, but does it help if they are? I actually have an unused ground rod that the subpanel grounds used to be connected to before the grounds were run back to the ATS. If it is a good idea to connect the subpanels to the unused ground rod (or the same ground rod that the ATS is connected to), what are the requirements for doing so?

3. I've also been researching ground considerations for phone and satellite dish (DirecTV). Currently, my dish is not grounded at all. My phone service NID is about two feet from the junction box mentioned above. There is a ground wire going from the NID to a nut/bolt the phone installer put into the side of the junction box. I guess he did that because there was no ground rod nearby (the only one being at the shop). After I add the ground rod at the house, should I ask the phone company to come out and run their ground wire to the new ground rod? For the satellite dish, should I run a ground wire from the dish to the new ground rod?

4. Back to the original topic of subpanels, grounds, etc...what is the reason for requiring a separate ground rod for the subpanel if it is in a different structure? It can't be distance since the structures could be close together. Is it because of the increased possibility that the ground or neutral could be damaged between the two structures? Or is it something else?

Lastly, I haven't checked in a while, but it used to be that around here (SE Texas, 15 miles from the coast), only one eight foot ground rod was required by city codes. I guess that was because most all the soil is heavy black gumbo clay, and it is always pretty wet when you get about two feet below the surface. If multiples are now required, are there guidelines on how they should be set up? Distance between them? Wiring guidelines, etc.?

Thanks,
Ira
 
  #22  
Old 10-08-09, 07:32 AM
B
Member
Join Date: Aug 2008
Location: Kansas
Posts: 233
Received 0 Votes on 0 Posts
So in order to add a ground rod, can I simply add another lug to the junction box similar to the lug the ground wire is connected to, and run a wire from that lug to the ground rod?
I believe a codes inspector would not have a problem with that... and would give you the exception for the grounding point at the junction box. However he would have a problem with the location of the dwelling disconnect being so far from the point of entrance of the feeder. He would likely require you to change out the junction box to a 200 amp disconnect enclosure and then allow you to run your grounding from it.

Ground rods or any grounding electrodes primary purpose is property protection from high voltage and amperage events like power line surges and lightning strikes to premises or nearby. They are not intended for human safety.

The equipment ground ran with the feeder and your branch circuits is bonded to all metal so that any ground fault has a low resistance/impedance path back to the transformer center tap (source). This is what allows your circuit breakers to open and clear ground faults.

Grounding electrodes and the earth path to the transformer ground rod will not allow enough current to flow to the source to open a breaker.

So in essence the GES (grounding electrode system) and the EGC (equipment grounding conductor) serve two entirely different purposes. The GES for property protection and the EGC for human protection from shocks. The 2 systems are bonded at the service equipment only because the fault current needs to utilize the service neutral to get to the transformer (source). Remember that current always seeks its source not earth...it will use earth to get there but will take the lower impedance path (service neutral) if available.

A few diagrams for you to ponder ....





As for the other sub-panels needing to be connected to grounds rods or the ATS ground it would serve no purpose to do so with the service entrance already containing the GES. It also could have a few issues with the right circumstances in place. So I wouldn't bother.

If you use the junction box at the house as your grounding point to a ground rod (use #4 copper to the electrode and acorn clamp it) and the ground is bonded to the box I see no reason to change the grounding for phone and comm/data. cable.

Separate structures require there own grounding electrodes to protect that property from high voltage events.

The number of ground rods is decided by a ground resistance test, However since you have no other electrodes (your water pipe is pvc you would likely be required to drive 2 rods. If the resistance to earth is 25 ohms or less then an inspector could allow you to drive only one rod. I don't see how you will know this though unless you hire someone with the necessary equipment to make a ground resistance test.

4. Back to the original topic of subpanels, grounds, etc...what is the reason for requiring a separate ground rod for the subpanel if it is in a different structure? It can't be distance since the structures could be close together. Is it because of the increased possibility that the ground or neutral could be damaged between the two structures? Or is it
something else?
The rod has nothing to do with the ground wire in the feeder or the neutral. It simply facilitates a path to earth for huge voltage events to help keep these voltages from sustaining damage to your property.

Earth is high resistance in respect to copper wire and metal. Voltages in residential systems 120/240 volts cannot get very much current to go to earth due to the resistance. Lightning on the other hand has little problem pushing current to earth. So earth becomes a valuable ally when trying to stabilize high voltage on your system wiring due to a lightning strike.

Hope this all helped
 
  #23  
Old 10-08-09, 08:45 AM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,163
Received 1 Vote on 1 Post
and you wanted to go fishing, Bruto.

Especially when you do such a great job explaining this here, why? You really do a great job with the explanations.
 
  #24  
Old 10-08-09, 12:20 PM
B
Member
Join Date: Aug 2008
Location: Kansas
Posts: 233
Received 0 Votes on 0 Posts
Originally Posted by nap View Post
and you wanted to go fishing, Bruto.

Especially when you do such a great job explaining this here, why? You really do a great job with the explanations.
Mother nature has a way of dealing delays to my fishing trips but if she is kind will be leaving for my next fishing adventure tomorrow evening.

Unfortunately I find it hard to not respond to some threads when I check in on the forums even though I have vowed to take a break and relax a bit. I'm trying hard to not turn the puter on and find other things to do.

Being retired I have a valuable thing, which is ...time. Time to explain things where as the many good electricians here and those that moderate may not have the luxury. I find it has a domino effect... if you teach one person to understand what he never understood it adds one more DIY that can correct another DIY's misconceptions. The key is an explanation that is clear and the person can 'see it' and then understands the why of it. I'm working on a drawing of this set up we are talking about here and may post it to this thread when I finish it. Generators cause a heck of a lot of confusion and differences of opinion and I'm not sure even if the suppliers and manufacturers understand it. The most controversy is operating a backup system for your home with a 'portable job site style generator" where neutral and ground are bonded at the generator due to the fact of plug in receptacles. These generators were really never meant to serve as dwelling standby power.

At any rate I'll probably pop in from time to time but I will definitely be more scarce till I get refueled.

Nice to hear from you just the same and thanks for the thumps up comments. The same back at you.
 
  #25  
Old 10-08-09, 12:43 PM
I
Member
Join Date: Jan 2008
Location: Texas
Posts: 123
Received 0 Votes on 0 Posts
Bruto...before you run off...

First, your explanations and drawings have been extremely helpful. I've always thought I knew how my system was supposed to be set up, but I never completely understood why. That put me at a disadvantage when the electricians I hired didn't like me questioning what they were doing. Now I understand the "why" as well as the "how".

I will take responsibility for the lack of a ground rod at my home. I did all of the electrical work from the mast at the shop all the way to and including everything in my home twenty years ago. I don't remember who told me I didn't need a ground rod at the house, or maybe someone told me I did but I didn't listen to them. Except for that ground rod, everything was correct (except maybe the junction box, too) until the electricians came around and started messing with the shop subpanels to put in the ATS.

I'm going to talk to an electrician (I trust the last one I hired) about replacing the junction box at the house with a 200A disconnect box. I can see why it is a good idea. Even though I can cut off power to the house by throwing the breaker in the 2nd shop subpanel, that certainly isn't obvious to others, and the shop may be locked.

So what do you recommend for grounding the satellite dish? It's mounted on a wooden chimney chase and the cables drop down the chase into the attic. It's about a forty foot run thru the attic if I were to try and run a ground from the dish to the new ground rod. I thought about sinking a ground rod specifically for the dish that would be maybe 25' away, but I guess that's not a good thing to do. I will have some type of individual surge suppressors in the attic on each individual satellite feed cable.

Since you mentioned putting together a drawing showing a genset in the mix...my genset has a ground rod next to it. There's a short cable bolted to the genset frame (there is a "ground symbol" stamped in the frame next to the bolt) that connects to that ground rod. The rod is about fifteen feet or so from the ground rod that the ATS is connected to, and there is no cable running directly between the two rods. I don't know if the frame's ground is connected internally to the ground wire going from the genset back to the ATS.

Thanks,
Ira
 
  #26  
Old 10-08-09, 03:00 PM
B
Member
Join Date: Aug 2008
Location: Kansas
Posts: 233
Received 0 Votes on 0 Posts
Your set up is a bit troublesome..

If you drive your own ground rod then you need to connect it to the building ground rod.....an example

http://www.diychatroom.com/attachmen...820.100-d-.jpg

or any of these electrodes

http://www.diychatroom.com/attachmen...00.40-b-1-.jpg

You also may have a discharge unit for the dish that needs grounding. I realize you don't have overhead at the house but I think you get the idea.



The reason you must connect what ever you end up doing to the electrical system ground rod is to prevent voltage potential differences and subsequent shock hazards to people and/or an increased possibility of greater damage to property in a lightning strike. The potential difference at the isolated ground bar if not bonded to the dwelling GES causes this event.. The grounding conductor to the rod must be #10 awg and not longer than 20 feet unless you drive your own rod within that distance or as close to it as possible then a #6 to the dwelling ground rod.

As for the ground rod at your gen set, I believe the instructions will say to do so if your gen set is going to be separately derived by switching the neutral at the ATS. If not then just do as the manufacturer wants. It essentially is to protect the gen set anyway.. though in your set up the dwelling ges is doing the same thing.

As for the disconnect at the house all I can tell you is what the NEC requires even though you are in an unincorporated area. The NEC requires a disconnect at all detached structures. Your problem is the location of your sub-panel that has the main breaker. The NEC requires the disconnect to be located at the nearest point of entrance of the feeder either outside or inside the structure. IMO it isn't the end of the world if you don't but consider a fire and the fire department trying to figure out or get the disconnect. I would certainly label the panel in the shop with House Disconnect....

Hope this was clear as mud....
 

Last edited by Bruto; 10-08-09 at 03:36 PM.
  #27  
Old 10-08-09, 05:00 PM
I
Member
Join Date: Jan 2008
Location: Texas
Posts: 123
Received 0 Votes on 0 Posts
Originally Posted by Bruto View Post
Your set up is a bit troublesome..
I think that's an understatement.

I guess I don't understand why running a #10 ground wire from the satellite to its own ground rod (may overshoot the 20' maximum by up to five feet) and then running a #6 underground fifty feet from the satellite ground rod to the dwelling ground rod is better than running a #8 (or even a #6) from the satellite directly to the dwelling ground rod for a distance of maybe a little less than fifty feet.

Wherever it ends up at, can the ground wire from the satellite travel inside the wooden chimney chase and into the attic before going back outside to the ground rod?

If the option of two ground rods is chosen, is there a requirement as to how deep the wire between them must be buried?

As you would probablye expect, the satellite dish (installed by a DirecTV installer) has no grounding systems on it at all right now. The only wires coming off of it are the four satellite feeds.

And subpanel 2 in the shop is labeled "house disconnect", but that assumes the fire dept knows about it and is willing to chop thru the shop door to get to it. I've heard sometimes they will just pull the POCO meter instead. But if they do that, my genset will start. Fortunately the genset and 500 gallon LPG tank are within plain site of the meter, about fifteen feet away. There is an external shutoff valve on the genset LPG line if they think clearly enough to shut the fuel off so the genset won't start. I've thought about putting a "notice sticker" next to the POCO meter stating that, and a big label on the genset showing where the shutoff valve is.

Thanks,
Ira
 
  #28  
Old 10-08-09, 05:24 PM
B
Member
Join Date: Aug 2008
Location: Kansas
Posts: 233
Received 0 Votes on 0 Posts
I guess I don't understand why running a #10 ground wire from the satellite to its own ground rod (may overshoot the 20' maximum by up to five feet) and then running a #6 underground fifty feet from the satellite ground rod to the dwelling ground rod is better than running a #8 (or even a #6) from the satellite directly to the dwelling ground rod for a distance of maybe a little less than fifty feet.
It's not any better IMO.... I believe you asked about driving an isolated rod for the dish so I was just explaining...
When you connect to the GES ground rod from any other ground rod the grounding electrode bonding wire must not be smaller than #6 copper. The same would hold true if you were connecting two ground rods to the disconnect on the house. Essentially it becomes part of the dwelling GES and must be bonded by a #6.

Here is the link to DirectTV's dish installation instructions for DIY applications. The grounding requirements are in these instructions......page 35

http://www.directv.com/learn/pdf/SelfInstallGuide.pdf





Where ever it ends up at, can the ground wire from the satellite travel inside the wooden chimney chase and into the attic before going back outside to the ground rod?
Sure...you would probably laugh if I told you they want the route to be straight as possible like an arrow....

Overall I don't think you have that many issues to resolve and none of them IMO are critical.
 

Last edited by Bruto; 10-08-09 at 06:17 PM.
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: