Sub Feed Ground

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Re: Sub Feed Ground

That being said, can we all agree that it is a better installation to run an ECG with the other conductors regardless. Treat the detached building panel as a sub panel, and separate the neutrals and grounds?
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Agreed. :) [/QB][/QUOTE]

Not so fast. :D

How is it different than the 8.9 gazillion services to buildings in the United States?

Think of it this way.

Often the grounded conductor is much larger than the required grounding conductor.

The larger conductor provides a lower impedance fault path.

Lets say a 100 feeder is running 1500' feet to a pump house with nothing around it.

Would the 8 AWG EGC be be better than a 3 AWG grounded conductor.

I have never personally used 250.32(B)(2) as I was trained to pull EGCs. That aside it is an option I might use in certain situations.

This is Bennie's domain.
 
Re: Sub Feed Ground

Originally posted by Samz:
If there is no EGC ran, and no other metallic paths back to service what is the neutral current path back to the service, since the neutral and EGC are bonded at the subpanel?
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There are none, which is why it's legal, per 250.32(B)(2). :)

But will it always stay that way? That's your call.
 
Re: Sub Feed Ground

"800.33"

My brand new 2005 pdf code book that was supposed to come with all the updates doesnt have that one. :confused:
 
Re: Sub Feed Ground

iwire 8.9 gazillion is alot of services.

and if the feeder calculations work for sub-panels in larger places, why would the EGC not clear a fault here?
 
Re: Sub Feed Ground

Originally posted by iwire:
I have never personally used 250.32(B)(2) as I was trained to pull EGCs. That aside it is an option I might use in certain situations.
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I have used it. Heck, in my short time, I've only had occasion to use (B)(2), working as the low-bid. I do as I'm told, if it's legal.

I believe the seperate EGC system is superior, for the fact that if an open neutral occurs, exposed metallic parts cannot become energized if there is an EGC run with the feeder.

I wish I was here when he was here. I've read some of his posts when I happen across them, and he was a very skilled man. :)
 
Re: Sub Feed Ground

There are none, which is why it's legal, per 250.32(B)(2).

Then what is the neutral path of the second building? The neutral conductor that is returning back to the main service? Thanks for th patience! :confused:
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Re: Sub Feed Ground

There are problems with both options. If you run the EGC, you can never know for sure it is effective or intact until it is needed, meaning that if a fault were to occur and the EGC is no longer properly connected, it could keep metallic parts energized.

Then again, this would be a problem with any typical electrical circuit. I think the obvious point is that both provide effectively the same "practical safeguarding" with both the same "pratical flaws".
 
Re: Sub Feed Ground

Originally posted by jbwhite:
iwire 8.9 gazillion is alot of services.

and if the feeder calculations work for sub-panels in larger places, why would the EGC not clear a fault here?
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It certainly could, unless the sub panel is 1,500 feet from the service panel.

Can we agree a larger conductor will cause the breaker to open faster?
 
Re: Sub Feed Ground

Originally posted by jbwhite:
800.100 has to do with communications circuits.

Did the OP mention a phone line? :confused:
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No, but if the two building in question had a bonded phone line per 800.100 than we could not even consider using 250.32(B)(2).
 
Re: Sub Feed Ground

Originally posted by iwire:
Originally posted by jbwhite:
iwire 8.9 gazillion is alot of services.

and if the feeder calculations work for sub-panels in larger places, why would the EGC not clear a fault here?
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It certainly could, unless the sub panel is 1,500 feet from the service panel.

Can we agree a larger conductor will cause the breaker to open faster?
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If the sub-panel is a gazillion feet from the main panel then ungrounded conductors have just as much voltage drop as the ground wire. ;)

When we increase the size of the ungrounded conductors for the voltage drop, we will increase the size of the ground wire.

I can see where the total resistance could be a greater if the conductor sizes are not increased, but I work in alot of industral buildings and the breakers all open just fine, and we run distances that would dwarf the average home. I cant see a problem here, unless the detached building is in the next county.
 
Re: Sub Feed Ground

Originally posted by Samz:
Then what is the neutral path of the second building? The neutral conductor that is returning back to the main service?
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Right. There can be only one path for neutral current legally.

250.32(B)(1) describes this:
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">EGC ran with outside feeder</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Neutrals and branch circuit EGC's are separate</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Grounding electrodes connect to Grounding Bar.</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Bonding (description below) is accomplished with the EGC of the feeder</font>
<font size="2" face="Verdana, Helvetica, sans-serif">

250.32(B)(2) describes this:
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Neutral conductor is used for bonding (causing circuit breakers to trip in the detached building, if a hot wire touches the EGC of a circuit in that building)</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Grounding Electrodes connect to the Neutral bar</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">You can't do this if there's an EGC with the outside feeder</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">You can't do this if there are metallic paths connected to the grounded electrically between the two buildings</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">You can't do this if there is equipment GFP on the feeder</font>
<font size="2" face="Verdana, Helvetica, sans-serif">
 
Re: Sub Feed Ground

Originally posted by jbwhite:
I cant see a problem here, unless the detached building is in the next county.
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So your postilion is that a smaller conductor for the fault path is better than a larger conductor? :p

Again I ask you to explain the difference between using 25.32(B)(2) and any typical service installation?

I agree entirely with Bryan

Originally posted by bphgravity:
I think the obvious point is that both provide effectively the same "practical safeguarding" with both the same "pratical flaws".
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Re: Sub Feed Ground

I agree that the phone is a seperate metalic path, regardless of the shield. I just didnt see where it was mentioned here before your post. :)


IMHO this whole topic is about weather or not to save the money by not having to run a full size ground, or use metalic raceway.

If it were me, (and it is not) I would run in pvc with a full size ground.
 
Re: Sub Feed Ground

iwire, to answer your question honestly than I will have to admit that in this case I think that we do need to build for possible future changes.

Meaning the addition of plumbing or phone or something else in the future.

This goes totally against what I have said in previous threads about not being required to build for changes in the future.

So, my bail out is that while this is not required it is a good idea.
 
Re: Sub Feed Ground

Originally posted by iwire:
Originally posted by jbwhite:
800.100 has to do with communications circuits.

Did the OP mention a phone line? :confused:
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No, but if the two building in question had a bonded phone line per 800.100 than we could not even consider using 250.32(B)(2).
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Bob,

This was my thought when I spoke about the phone line being properly installed. Maybe I should have said possibly installed according to 800.100. Chaulk it up to an early AM faux pas.
 
Re: Sub Feed Ground

Originally posted by georgestolz:
Originally posted by iwire:
So your position is that a smaller conductor for the fault path is better than a larger conductor? :D
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So I must assume you do not install any services as they are dangerous?

That's a real question.

Under 250.32(A) how do you know the EGC is intact?
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