Ground Ring?

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GG

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Hello. I have to run a #6 ground ring around a 12X12 communications building. The communications building only requires 2 - 15 amp circuits, and is 210' from the nearest electrical panel. I was going to run a 40 amp circuit to feed a 70 amp outdoor panel. I will be using 6/3 UF cable that has a #10 ground wire. Will I need to run a #6 ground wire with my feeder wires to connect to the #6 ground ring? Maybe someone here can think of a better way to install this than what Im picturing. TY.
 
GG,This is a feeder to an outbuilding.The #10 egc is ok to the building.The #6 ground ring needs to be bonded to the disconnecting means with the same # 10 egc.Where did you come up with the #6 ground ring?If no electrodes are present, and your using a ground ring as a grounding electrode, it must not be smaller than #2awg.
Rick
 
Yes Rick your right, I will need a #2 wire for the ground ring. So with the #2 installed can I then run a #6 bonding wire from the panel to the ground ring or do I need to run the #2 ground ring all the way to the panel? There will be an 8' ground rod installed, but Im guessing I will still need to use a #2 for the ground ring? TY.
 
Ty,The #2 awg used for the ground ring should be brought into the disconnect.The connection to the gound rod if only to the rod from the disc. can be a # 6 ,but if you already have the # 2 out there, i would connect it to the rod.
Rick
 
Re: Ground Ring?

GG said:
I was going to run a 40 amp circuit to feed a 70 amp outdoor panel. I will be using 6/3 UF cable that has a #10 ground wire.
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As described you likely will have a violation of 250.122(B).

You increased the size of the circuit conductors so the EGC will have to be increased proportionally.

Bob
 
Re: Ground Ring?

iwire said:
GG said:
I was going to run a 40 amp circuit to feed a 70 amp outdoor panel. I will be using 6/3 UF cable that has a #10 ground wire.
Click to expand...

As described you likely will have a violation of 250.122(B).

You increased the size of the circuit conductors so the EGC will have to be increased proportionally.

Bob
Click to expand...


Bob, you bring up an interesting point. It seems odd that a 6/3 cable could be used on a 60 amp circuit but not a 40 amp one.
 
I did some calculations and find that in order for you to use 6 AWG circuit conductors protected by a 40 amp breaker you will need a minimum equipment grounding conductor size of 8 AWG per the requirements of 250.122(B)

The first step is to find the circular mils of the conductors in Chapter 9, Table 8

10 AWG = 10,380 circular mils

8 AWG =16,510 circular mils

6 AWG - 26,240 circular mils

Now we must find the ratio of increase of the circuit conductors.

26,240 / 16,510 = 1.58 ratio

Now we apply that ratio to the EGC

1.58 * 10,380 = 16,400

This tells us we need an EGC of at least 16,400 circular mils, that is at least an 8 AWG.

Strangely if you use a 60 amp breaker in place of the 40 amp breaker with the 6 AWG UF you could forget all about 250.122(B)

by Infinity
Bob, you bring up an interesting point. It seems odd that a 6/3 cable could be used on a 60 amp circuit but not a 40 amp one.
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I was composing this post while Trevor posted the above.

But I agree that 250.122(B) can result in odd results.
 
But Bob, don't you think that a #10 EGC in a cable with #6 conductors that is protected at 40 amps is already increased in size? 250.122 tells me that I can use a #10 EGC with #6 conductors. Typically #6 conductors can be protected at 60 amps. Logically, IMO this would mean that a #10 EGC is used at 40 amp it is already large enough.
 
infinity said:
But Bob, don't you think that a #10 EGC in a cable with #6 conductors that is protected at 40 amps is already increased in size?
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No.

It hinges on the wording of 250.122(B)

250.122(B) Increased in Size. Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to circular mil area of the ungrounded conductors.
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The circuit conductors increased in size, 250.122(B) requires the EGC to be increased.

No exceptions.

A 40 amp circuit normally requires a 10 AWG EGC and that is the size the ratio must be applied to.

I am not sure of the logic but I am sure of the code on this subject.

250.122(B) basically kills the use of cable assemblies when over sized for any reasons.
 
I think that 250.122(B) needs to contain more information than it does to avoid installation quagmires like this one. If the #6 cable is not used for voltage drop, say he just had it on the truck, than we don't even have this conversation.
 
Thanks for the responses. So it looks like if I want to use my 6/3 UF cable Im going to have to place the feeder on a 60 amp breaker. This shouldnt be a problem as the load of the bldg. will only be about 25 amps.
 
infinity said:
I think that 250.122(B) needs to contain more information than it does to avoid installation quagmires like this one.
Click to expand...

I agree it makes for some oddities but at the same time I have seen Byran and Charlie B say that it actually makes sense.


infinity said:
If the #6 cable is not used for voltage drop, say he just had it on the truck, than we don't even have this conversation.
Click to expand...

That is false since 2002.

In the 1999 NEC it said this.

1999
250-122()(b) Adjustment for Voltage Drop. Where conductors are adjusted in size to compensate for voltage drop, equipment grounding conductors, where installed, shall be adjusted proportionately according to circular mil area.
Click to expand...

The 2002 NEC took away all references to voltage drop.

2002 NEC
250.122(B) Increased in Size. Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to circular mil area of the ungrounded conductors.
Click to expand...

Now for better or worse no matter what the reason the circuit conductors where increased for we have to apply 250.122(B).
 
Trevor I do agree with you that it is at best an odd section of code.

If we where talking 15, 20 and 30 amp circuits it really gets odd. :shock:
 
I guess the ground ring is for communications equipment, equipotential point requirements. if it is I recommend 95sqmm or 3/0 for strenght and lower resistance.

davidv
es
 
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