Ground Bushings and EMT

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  #1  
Old 10-08-06, 04:24 PM
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Ground Bushings and EMT

Can someone tell me when I need to use ground bushings with EMT, and how to correctly wire them?

I have a 200A main/service disconnect feeding 2 100A subs, each independently connected with 2" EMT, currently with no ground bushings.


EDIT:

Also, I am following the grounding conductor from the water service. It enters the first sub panel, and ends at the isolated ground bar. From there, another grounding conductor is run from the ground bar of that panel, through the EMT, and to the shared neutral/ground bar on the main/service disconnect. Finally a 3rd grounding conductor is ran from the shared neutral/ground of the main panel, through EMT, and to the 2nd sub, where it ends at an isolated ground bar. Does that sound correct?
 

Last edited by JoeTheZombie; 10-08-06 at 04:39 PM.
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  #2  
Old 10-08-06, 09:36 PM
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Zombie you stated:

Also, I am following the grounding conductor from the water service. It enters the first sub panel, and ends at the isolated ground bar. From there, another grounding conductor is run from the ground bar of that panel, through the EMT, and to the shared neutral/ground bar on the main/service disconnect. Finally a 3rd grounding conductor is ran from the shared neutral/ground of the main panel, through EMT, and to the 2nd sub, where it ends at an isolated ground bar. Does that sound correct?
Kinda hard to follow your statement but let me see here....

# 1- how come your connection to the water pipe is not going back to the main distribution panel to connect to the neutral/grounding buss bar?

# 2 - You state the sub panel has a isolated ground bar...when it should be a isolated neutral "grounded" conductor bar in the "Sub" panel.....

# 3 - If you are using EMT...why did you run a seperate grounding conductor?...is the EMT not continuous?

# 4- You continue to say isolated ground bar.....where as in a sub panel the ground bar is not isolated..it still bonds to the panel why its mounting nature...it is the Neutral " grounded" bar that is isolated.

In regards to your question about ...that would be bonding bushings......

Concentric or eccentric knockouts must always have a bonding bushing on the service side but at only one location. In regards to your EMT question I will assume to the sub panels....many of the lockrings today if driven to the point it bites down into the enclosure and removes the paint or lacquer of the equipment is considered suffient.

Now..if you use reducing washers and such....bonding jumper is required....
 
  #3  
Old 10-09-06, 09:47 AM
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Thanks for the response.

#1- I don't know why it was run this way. I always thought the grounding conductor needed to be an unbroken connection from the water service entrance to the main panel. This installation, as I stated, has the grounding conductor terminating at sub1 first, probably because it is a good deal closer to the water service entrance. There is then another grounding conductor that is run from the grounding bar in this panel, to the main panel, where it is bonded with the neutral. I was inquiring if this is a problem.

#2- Perhaps the term "isolated" was incorrect. I was trying to relay that the neutral bar and the grounding bar were isolated from each other, not that the grounding bar was isolated from the panel.

#3- I didn't run the EMT, but there are compression fittings on the ends of the EMT to provide threaded ends for panel attachment. I don't know if the compression fittings didn't meet grounding conductor requirements or not, but there is a bare #4CU run throughout the EMT.

#4- See #2.

Although the general home inspector said these "issues" were allowable, I'm not so sure. I was seriously burned by a home inspector on my last house purchase, that required a very expensive electrical service upgrade, and I don't want to be burned again.

My question about grounding bushings was derived from information I read requiring the EMT to provide electrical continuity to the grounding conductor. Are you saying the threaded compression fittings on the ends of the EMT, along with the bite-in nut are enough to provide this? You are saying that grounding bushings are not required in this installation?
 
  #4  
Old 10-09-06, 10:15 AM
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> there is a bare #4CU run throughout the EMT

> My question about grounding bushings was derived from
> information I read requiring the EMT to provide electrical
> continuity to the grounding conductor.

In your case, the bare #4 provides primary grounding instead of (actually, in addition to) the EMT. The bonding bushing would keep the metal conduit from becoming energized in the event a hot wire broke inside the conduit.

> Are you saying the threaded compression fittings on the
> ends of the EMT, along with the bite-in nut are enough to
> provide this?

Often, yes.

Given that you have EMT compression fittings, lockrings, and a bare EGC in the conduit, I can't imagine a situaiton where the bonding bushing would do more than what you already have. The entire length of bare #4 wire is laying metal-to-metal inside the EMT.
 
  #5  
Old 10-09-06, 12:27 PM
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Yes your main grounding electrode conductor to your water source is not correct.

It should run as one continous run all the way to the main electrical panel. Even if in doing so it passes directly by a sub panel.

Splices can only be made with welds or irreversable connectors.

If it is run in metal conduit it must be bonded to the conduit at both ends with the proper fittings.
 
  #6  
Old 10-09-06, 01:57 PM
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Thank you, jwhite.

So if I am understanding correctly, I will need the grounding bushings on both sets of EMT, on both ends; the bare grounding conductor clamped to those bushings at all 4 locations.

Hmmm, to rectify the mis-wiring of the grounding conductor brings up further questions.

I would also remove the existing grounding conductor from the water service that terminates at the first subpanel, but can I run a new grounding conductor from the water service to the main panel through the first subpanel EMT? This would mean there would be two grounding conductors in this EMT run. One from the water service to the main, and one from the main to the first subpanel. Which one would need to be bonded to the EMT, or would they both?

I can now somewhat understand why it is wired the way it is.
 
  #7  
Old 10-09-06, 02:59 PM
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No, I better try to explain again.

You cannot run the ground from the water into the sub panel.

sometimes people run a ground in conduit to give it support. If that conduit is metal special bonding bushings need to be used at each end. You can just not run that wire in conduit.

Again. the ground from the water does not go into the sub panel.

The grounds between the sub panels and the main panel stay in tact. But I do not see the need for bonding bushings on those.
 
  #8  
Old 10-09-06, 03:54 PM
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I do not want to run the the ground from the water service to the sub panel. I want to run it to the main panel by way of the existing EMT that connects the main panel (outside) to one of the subpanels (inside) that is near the water service. Are you saying I can not do that? What if I use an insulated conductor? If not, I will have to run new conduit outside to the main, which would be a major pain.


I am still confused about the grounding bushings. :-\

First you say,

> If it is run in metal conduit it must be bonded to
> the conduit at both ends with the proper fittings.

But then

> The grounds between the sub panels and the main
> panel stay in tact. But I do not see the need for
> bonding bushings on those.

?
 
  #9  
Old 10-09-06, 04:16 PM
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He is talking about two different things:

1) The Equipment Grounding Conductor (EGC) - this runs by way of the EMT from the main panel ground bar to the subpanel ground bar. This does not require bonding bushings.

2) The Grounding Electrode Conductor (GEC) - should run unbroken from the main panel ground bar to the water pipe entrance. The GEC does require bonding bushings if it runs through metal conduit, however conduit is optional for the GEC. The GEC should not share the existing conduit with the subpanel feeders.

In your case, the installer ran the GEC to a subpanel instead of the main panel. The way to correct the problem is to leave the existing conduit as-is and to run a new GEC (#4 copper) from the water pipe to the main panel ground bar. You can extend the existing GEC from the subpanel location if you attach the new piece of wire with an irreversible compression fitting.
 
  #10  
Old 10-09-06, 04:54 PM
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Originally Posted by JoeTheZombie
Thanks for the response.

#1- I don't know why it was run this way. I always thought the grounding conductor needed to be an unbroken connection from the water service entrance to the main panel. This installation, as I stated, has the grounding conductor terminating at sub1 first, probably because it is a good deal closer to the water service entrance. There is then another grounding conductor that is run from the grounding bar in this panel, to the main panel, where it is bonded with the neutral. I was inquiring if this is a problem.

ANSWER: As stated...the GEC should be continuous to the Main Panel...not the Sub Panel. I agree with the suggestion to re-run this as a # 4 AWG CU and solve the problem.

#2- Perhaps the term "isolated" was incorrect. I was trying to relay that the neutral bar and the grounding bar were isolated from each other, not that the grounding bar was isolated from the panel.

ANSWER: Gotcha.....it is important to understand that because the netural on the "Sub" panels should be isolated and floating...in other words if you took a cont. tester you would not get a reading between the Neutral Bar and the Grounding Bar.....Isolated....

#3- I didn't run the EMT, but there are compression fittings on the ends of the EMT to provide threaded ends for panel attachment. I don't know if the compression fittings didn't meet grounding conductor requirements or not, but there is a bare #4CU run throughout the EMT.

ANSWER: Compression fittings should meet it with regards to the EMT and being the EGC....they just probably did not know this...not that the additional EGC will harm anything....now if you had a sub panel that was incorrectly wired and the neturals and grounding conductors terminated on the same bar..and you had that EGC in the metal pipe...then you may have some issues but not the EGC.

#4- See #2.

Although the general home inspector said these "issues" were allowable, I'm not so sure. I was seriously burned by a home inspector on my last house purchase, that required a very expensive electrical service upgrade, and I don't want to be burned again.

My question about grounding bushings was derived from information I read requiring the EMT to provide electrical continuity to the grounding conductor. Are you saying the threaded compression fittings on the ends of the EMT, along with the bite-in nut are enough to provide this? You are saying that grounding bushings are not required in this installation?

ANSWER: now in regards to the bonding bushings..read my statement again....you only need to do so at the service Line side in your case.....and as stated if you have the GEC run in conduit..it also needs bonding if run in conduit.....as explained you would probably be better served using Solid # 4 AWG CU...unless your area does not allow it...check with your local AHJ.
My responses are embedded in your QUOTE....
 
  #11  
Old 10-10-06, 04:04 AM
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In addition joe
Do not put the wire to the water pipe in the same conduit with any other wires.
 
  #12  
Old 10-10-06, 08:47 AM
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OK, so the repair would be to install a new conduit from the water service to the main panel, with the grounding conductor bonded to the conduit at both ends. Also, remove the existing grounding conductor from the water service to the subpanel.

I really do not want to run a new conduit. Is the reason I can not use the existing EMT because we are concerned about the GEC contacting the EGC? Wouldn't using an insulated conductor solve that problem? Oh, but then I couldn't bond the GEC to the metal conduit it is run through... Hmm. OK I think I now know what you guys are talking about.

Thanks for the help and information.
 
  #13  
Old 10-10-06, 09:01 AM
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The GEC to the water does not need to be in couduit. You can just staple up if you have a crawl space, or drill holes in the wood if you have a basement.

I was trying to get out of this explaination because I do not know if I can discribe it right.

If the GEC has to relieve a lighing strike or some other objectionable current, it can be forced to handle Kilo volts for a few seconds. The voltage going through the GEC will induce voltage in a metal conduit, if it is in one, or into other wires, if it were in the same conduit.

The result can be that the GEC blows apart before it finishes doing its job, or objectionable current can be forced on other parts of the system, in effect creating the problem that the GEC is intended to eliminate.

If I did not explain that well, someone feel free to help me out.
 
  #14  
Old 10-11-06, 09:54 AM
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[QUOTE=ElectricalMan]ANSWER: Gotcha.....it is important to understand that because the netural on the "Sub" panels should be isolated and floating...in other words if you took a cont. tester you would not get a reading between the Neutral Bar and the Grounding Bar.....Isolated....QUOTE]

Actually, and this is just a nitpick, you would see continuity between the neutral and the grounding buss bar in the subpanel. The neutral and grounding busses are still electrically connected, it's just at the main panel rather than the subpanel.
 
  #15  
Old 10-14-06, 07:31 PM
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Arnie- I was refering to the bar itself in theory...not hooked up with wires on it.

Was trying to explain that the reading on an isolated bar should not detect cont. if done correctly on a sub panel.....the theory of it...not the actuall application with wires attached....sorry was using the best example to explain the isolation...
 
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