Grounding, detached garage, whats required?

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  #1  
Old 09-22-07, 02:02 PM
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Grounding, detached garage, whats required?

The garage is steel framed, steel skinned, sitting on a concrete pad. Right now I have 2, 20amp circuts, 12 gage wire, that share a neutral, (a black, red, and a white) its a 100' home run to the main panel buried in PVC conduit that changes to metal in the garage and the house. There is no ground wire from the house to the garage. 2 of the 7 recepticals have a ground wire thats just screwed to the back of the box. Does this mean that the building is the ground, since the conduit isn't insulated from the building? Is this ok? Is there any thing I should change to get this up to snuff?
 
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  #2  
Old 09-22-07, 02:17 PM
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there one question it kinda bother me i know you say you brought black red,white but where is the green wire ??

normally it should have green wire in the conduct if so please post it asap

thanks
 
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Old 09-22-07, 02:43 PM
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There is actually a way to not have a grounding conductor required but the simplest method would be to provide one from the house to the garage. You do not need a grounding electrode system when doing this with only the circuits you have listed.

the neutral must be kept isolated from the ground in this situation.

also, from your situation, you must be sure that the metal conduit is properly bonded to its respective grounding system. Without going into to many details the simplest manner to do this woudl be to install a bonding bushing on the conduit as it enters the panel or first box in the garage and attach a ground wire from that bushing to the local ground system.
 
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Old 09-22-07, 03:57 PM
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There are two different grounding condutors to consider here. One is the GEC (grounding electrode conductor). The GEC bonds the electrical service to your grounding electrode (building steel, ground rod, water pipe, ect). The metal frame can be considered to be a grounding electrode if it has 10' or more directly in contact with the earth or incased in concrete that's in direct contact with the earth. I'm guessing that neither apply to your garage. Your best bet is to have a ground rod that's bonded to the steel frame and the equipment ground via a GEC. The GEC must be at least 8 AWG CU or 6 AWG AL wire. If you have a GEC smaller than 6 AWG, it has to be protected in conduit. 6 AWG does not have to be installed in conduit if it's properly secured.

The ground that you are asking about is the EGC (equiptment grounding conductor). The EGC provides a pathway from your devices (outlets, lights, ect.) back to the ground bus in the panel. You should have a 12 AWG ground running from the garage back to the main panel. Metal conduit it permitted as an EGC, but obviously the pipe run to the house is not continually metal. I wouldn't use the conduit as an EGC in buried or outdoor installations anyways because of corrosion. The devices will be OK just being grounded to the box if the box is metal and the circuit's piped with EMT all the way back to where the power comes in (but only after you've run the EGC and GEC).

A couple other things to consider: The power coming into the building should have a disconnect at the point of entrance. In your case, this can be done with a 20 amp / 277 volt double pole (not to be confused with a 4-way) switch. The GEC and the EGC should be bonded at this point as well.
 
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Old 09-22-07, 04:19 PM
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brew: due to the limited power (one MWBC) code does not require a grounding electrode system but it does require a EGC to be brought with the feeds.

as well, if this steel framed building has a concrete foundation with the minimum requisite length and size of rebar, that is considered to be an effective grounding electrode and a rod would not be required.

and the neut and the EGC should NOT be bonded at the garage in the OP's situation UNLESS there is no other metallic pathways between the house and garage AND a EGC is not used from the house to the garage.

and you are wrong on the size of the GEC.

and the reason for bonding the steel conduit is because it is required to be and the bond bushings may not be needed but I do not have the facts to say yes or no.
 
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Old 09-23-07, 09:18 PM
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Nap, I don't know how much of the message you were directing towards my post. I wish that you would've been more specific. You were right about the grounding electrode. I missed the very last sentence to the exception of article 250.32 (A) that says that a multiwire branch circuit shall be considered a single branch circuit for that section of the code. In other places, they're considered seperate circuits. I jumped the gun on that one.

As for the frame of the building for an grounding electrode, I'm not quite sure I get your reasoning. In order for the frame to be considered a grounding electrode, it would have to be bonded to the rebar. Right??? We don't know that it is. I surely didn't diclude it 100%, I just suggested that it'd be good to have a ground rod to be on the safe side.

I'm also not sure what you mean I am wrong about the GEC size. You didn't state a correct size or reference to explain. I got the sizes #8 CU and #6 AL from table 250.66. I recommended a #6 because of article 250.64 (B) which states that #6 can (where protected from physical harm) be run outside of conduit. According to that same section, anything less would require conduit. All this is moot, because you're right, a grounding electrode system isn't required in this case, but I'd like to know where you're coming from.

I don't know if you were directing the comment about bonding the neutral and the EGC towards me or trus-rod. Just to clarify, I did not suggest that. I only mentioned bonding the GEC and EGC at the point of entrance. I'm also unclear if you were implying that I suggested that the steel conduit did not have to be bonded. I did not. I agree with you on that one. I was only stating that, if the conduit is properly bonded (like you suggested), a ground wire as an EGC was not required for the devices. The conduit then would be the EGC and ground pigtails from the back of the box would be suffice.

Thank you for catching my mistake about the grounding electrode system nap. I will store that one in my memory from now on. Please help me further by explaining your reasoning.
 
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Old 09-24-07, 04:03 PM
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You were right about the grounding electrode.
Ok.

As for the frame of the building for an grounding electrode, I'm not quite sure I get your reasoning. In order for the frame to be considered a grounding electrode, it would have to be bonded to the rebar Right??? We don't know that it is. I surely didn't diclude it 100%, I just suggested that it'd be good to have a ground rod to be on the safe side.
that is what I said and since it is now a code requirement to bond to the rebar if there is enough length of the requisite size, all I was saying is that is adequate if it is as such.

grounding electrode system isn't required in this case, but I'd like to know where you're coming from.
Now, I blew it on that one. I am so used to larger services that I actually forget to use 250.66 and end up with #6 cu for all GEC to rods and #4 cu to the ufer.

I don't know if you were directing the comment about bonding the neutral and the EGC towards me or trus-rod. Just to clarify, I did not suggest that.
Thank you for catching my mistake about the grounding electrode system nap. I will store that one in my memory from now on. Please help me further by explaining your reasoning.
actually you did, in this statement from your post.

The GEC and the EGC should be bonded at this point as well.
part of the problem is that there are several ways to do what OP is doing and each of them have different requirements of bonding and grounding.

1. if this is installed per 250.32(A) as a single circuit(or as accepted by NEC, a MWBC), an EGC is required to be carried with the feeders and there is no grounding electrode system required.

The ground EGC and neut do NOT get bonded at the garage in this system/

this method is simply the installation of a branch circuit just as if the buildings were connected.

2. carry an EGC with the feeders.

this is generally the best system (in my mind).

the EGC and the Neut are NOT bonded at the garage.

this method is the same as installing a sub panel within a building except with the inclusion of a grounding electrode system.

3. no EGC with the feeders.

this can only be used IF there are NO other metallic bonds from the supply and load panels. A telephone wire or any other metal wire running from the house to the garage disqualifies this method from use.

A grounding electrode system must be employed and this is the only time the EGC and the GEC are bonded (just as any other main service in a builing.)

this is exactly the same as a main service in any typical building
-------

of all the things you posted, this was the one that actually concerned me. I read you bonding the GEC and the neut at the garage as well as running a EGC from the house to the garage.

This is strictly forbidden as the EGC will be carrying current proportionately to the resistance of the EGC as compared to the system neut.

Not a good thing if you pull the ground anywhere between the house and the garage believing it simply to be a EGC when in reality, it is a neut.
 
  #8  
Old 09-24-07, 04:40 PM
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This part is way above any DIYers head... I bet 1 in 50 get this part right.
 
  #9  
Old 09-24-07, 06:04 PM
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Originally Posted by Chris75 View Post
This part is way above any DIYers head... I bet 1 in 50 get this part right.
You are probably correct but getting it wrong can be deadly. So I, and others (including brewcity) try to make sure a question is answered as correctly as possible so as to minimize any hazards and to be installed to NEC.

Sometimes the conversation does go over the OP's head and even the original question but much of it is simply to allow each member advising an opportunity to support their advice. It helps make sure that the OP recieves the most correct advice that the collective DIY forums can supply.

As to the 1 in 50? I hope it it is more than that. If they would come here to DIY forums, we could be sure they do get it correct.
 
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Old 09-24-07, 08:48 PM
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I can definitely attest that this discussion has been helpful, even if it goes beyond perhaps the original question's scope. Long, detailed replies outlining all the possible ways to do something like this, and how, are some of the best "meat" of this forum!
Kudos to you guys!
 
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Old 09-24-07, 09:12 PM
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we always try to make sure you get what you paid for around here

I have even seen disgruntled (just curious, has anybody ever seen anybody that was "gruntled". I have only heard of disgruntled folks) members offered their initition fees AND all the monthly dues paid to date when they did not get what they paid for.
 
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Old 09-25-07, 10:58 AM
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"Bonding of ---- Exposed Stuctural Steel"

Please allow me to mention Art. 250.104 (C) Structural Steel which requires Bonding such steel that is "not (already ) intentionaly Grounded" .

It's indefinite if the steel of the stucture under discussion has already been Bonded to Ground in compliance with the Code . but in the interests of saftey from shock-hazards , I advise that this be done in order to emlinate all doubt.

He MAY need a Grounding Electrode to effect this.
 
  #13  
Old 09-25-07, 12:53 PM
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Nap, there's a difference between the neutral (grounded conductor) and the EGC (equiptment grounding conductor). I was suggesting that he bond the grounding electrode conductor with the equiptment grounding conductor, not the neutral.

Thank you PATTBAA. That is exactly what I meant about the GEC, but I think you stated it better.
 
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Old 09-25-07, 02:49 PM
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[QUOTE=brewcityc;1234509]Nap, there's a difference between the neutral (grounded conductor) and the EGC (equiptment grounding conductor).
QUOTE]

yep, I know that.

Sorry guys. My head has been on backwards a bit lately.
The video store my daughter works at was robbed (with her there) and I have been running very low on sleep. I have been trying to keep my mind off the situation and in my fatigue and lack of concentration, I have simply screwed up.

Nobody got hurt but it does have a very drastic phsychological effect on both her and me. I was robbed at gunpoint when I was 18 and I understand what it can do to a person.

My aplogies to all I have offended and miscorrected.

Next time, simply whack me and tell me to shut up when I am driving down the wrong road.
 
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Old 09-25-07, 03:27 PM
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Well, I'm gruntled. I'm a DIY'r, but you havenít gone completely over my head.

To explain it better, I have 1, 20 amp 220 circuit, or it could be, to the garage, but its wired as 2 separate 20 amp 110 circuits, one for lights and one for power. Is this wrong? The way I interoperate is one circuit could be considered a "metallic pathway" requiring a ground with the feeder of the other circuit. I'm planing to add a switching wire anyways.

Then the grounding, the outlets are bonded to the junction box and conduit system, and the conduit is either clamped or bolted to the steel framing. So the building is bonded to the ground that doesn't exist. So, if I add a ground feeder, is the bonding properly done?

Thanks again.
 
  #16  
Old 09-25-07, 03:35 PM
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According to your original post it is NOT wired as two separate circuits. It is wired as a multi-wire circuit, which is allowed.

However, you cannot add additional circuits. You can have a switched wired for a light, but that does not count as a circuit.
 
  #17  
Old 09-25-07, 04:31 PM
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So 2 breakers, a black wire to one and a red on the other, that share a nuetral is 1 multi wire circuit?
 
  #18  
Old 09-25-07, 05:19 PM
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Don't sweat it Nap. I've been guilty of the same thing before. I'm sorry about your daughter. I imagine it scares you a lot as a father. Because this is a family friendly site, I can't describe what I'd like do to her assailant(s) if that happened to my daughter. Hope you and your family are holding up OK.

Pretty good understanding trus-rod. I think I threw you off with the single branch circuit that I mentioned before. You do have 2 circuits, making up a multiwire branch circuit (because they share a neutral). The single circuit was with regards to the exception to the code requiring a grounding electrode. I thought that you needed it because it's required for more than one circuit. What I had missed was that the exception to the code considered a multiwire branch circuit as a single circuit for this section. So it's only considered as a single branch circuit for that purpose. It is otherwise considered seperate circuits in other sections.

Don't forget that if you don't already have a disconnecting means in the garage, you need one. This can simply be a 20 amp/ 277volt double-pole switch and should be located where the power comes into the garage.

The equiptment ground off the panel is all you need for grounding. You don't have to pull a ground wire with the circuiting in the garage and you don't need a ground rod. Keep in mind though that it's not "REQUIRED". If I had a large metal structure, I'd feel better knowing that I had more than a #12 ground bonding it to the earth. I'm not trying to scare you into anything. You should have GFCI protection on the outlets anyways. I would (this is not required, merely suggestion) at least protect the lighting circuit with a GFCI if you don't add a ground rod. This can be done cheaply with a seperate GFCI outlet.

Just to clarify what racraft said, you CAN actually run more circuits out to the garage, but then a grounding electrode will be required. Just keep in mind the amount of allowable pipefill. You should be OK adding 2 extra wires, but if you want to add more in the future you sholud check to see how many are allowable. Schedule 80 PVC is only good for 6 - #12's for example....
 
  #19  
Old 09-25-07, 05:54 PM
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Originally Posted by brewcityc View Post
Just to clarify what racraft said, you CAN actually run more circuits out to the garage, but then a grounding electrode will be required. Just keep in mind the amount of allowable pipefill. You should be OK adding 2 extra wires, but if you want to add more in the future you sholud check to see how many are allowable. Schedule 80 PVC is only good for 6 - #12's for example....

Brewcity:

hate to barge ya in this for a min but please excuse my pun for a min.

if i recalled somewhere in the NEC code they allowed one MWBC going to the detached resdentail garage and not allowed add more circuits the reason why i say this because in case someone try to do the troubleshooting with multiples of MWBC which i think it is not very festable and have to put a subfeed box there and let me point out is that the source have to be marked where it can be disconnected in case of repairs. if is not correct please refer the correct number on the NEC

THanks

Merci, Marc
 
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