EGC size

[infinity]

I have a lighting relay panel which is fed with #6 THHN from a 3 pole 20 amp breaker. The lugs on the panel accept 400 kcmil-#6 AWG conductors. What size EGC is required? I say #12 due the lug size, others say #6 due to 250.122(B). Which is it?

 

[raider1]

I have a lighting relay panel which is fed with #6 THHN from a 3 pole 20 amp breaker. The lugs on the panel accept 400 kcmil-#6 AWG conductors. What size EGC is required? I say #12 due the lug size, others say #6 due to 250.122(B). Which is it?

Great question!

IMHO, reading 250.122(B) you would need to use a #6.

Chris

 

[Dennis Alwon]

I have a lighting relay panel which is fed with #6 THHN from a 3 pole 20 amp breaker. The lugs on the panel accept 400 kcmil-#6 AWG conductors. What size EGC is required? I say #12 due the lug size, others say #6 due to 250.122(B). Which is it?

Trevor- what does the lug size have to do with it? The #12 is smaller than #6 and wouldn't work. You could pigtail a #6 to the #12 but I believe 250.122(B) is involved here.

 

[iwire]

The EGC would have to be 6 AWG per 250.122(B).

 

[infinity]

I disagree with the required #6. The smallest conductor permitted for this installation is #6 due to the size of the lug. Nothing has been increased in size therefore from table 250.122 #12 is all that's required.

 

[stickboy1375]

I'm going with even though you didnt want to increase the wire size, you still did.

 

[iwire]

I disagree with the required #6. The smallest conductor permitted for this installation is #6 due to the size of the lug. Nothing has been increased in size therefore from table 250.122 #12 is all that's required.

The lug size has little to do with it, you could work around that.


No matter what reason the circuit conductors have been increased for, 250.122(B) requires the EGC to be increased. With 20 amp circuits the EGC to circuit conductor size ratio is 1:1 and that must be maintained. A real bummer if you ran cable.

 

[Dennis Alwon]

I disagree with the required #6. The smallest conductor permitted for this installation is #6 due to the size of the lug. Nothing has been increased in size therefore from table 250.122 #12 is all that's required.

Where does it say that the lug comes into play? As Bob & I have said you can work around the lug issue. I say #6...:smile:

 

[celtic]

Here is a nice explanation taken from a similar recent thread:

The math is simply for wire sizes #14, 12, & 10. If you must increase the size of the ungrounded conductors then the egc must also be upsized proportionately. This means that any of the EGC sizes mentioned above will increase to the size of the ungrounded upsize.

This does not hold true for other sizes.

George did a nice explanation here

I say #6....anyone that disagrees can blame George

 

[C3PO]

I have a lighting relay panel which is fed with #6 THHN from a 3 pole 20 amp breaker. The lugs on the panel accept 400 kcmil-#6 AWG conductors. What size EGC is required? I say #12 due the lug size, others say #6 due to 250.122(B). Which is it?

Are the ungrounded conductors from the panel to the relay panel 12awg and then pigtailed to 6awg to go into the lugs or is the whole length of the circuit 6awg?

 

[infinity]

Where does it say that I must use a #12 conductor? A #12 would violate the listed usage of the lug which, in this installation, is one component of the entire circuit, that also happens to determine the minimum conductor size. The minimum is #6 on a 20 amp CB, so what has been increased? A #12 conductor is not permitted, neither is a #10 or #8 so how can a #6 be considered an increase in conductor size when it's the smallest conductor permitted for this circuit?

 

[infinity]

Are the ungrounded conductors from the panel to the relay panel 12awg and then pigtailed to 6awg to go into the lugs or is the whole length of the circuit 6awg?

The four circuit conductors are #6 THHN.

 

[C3PO]

Here is the code section and a staff note from NECplus.org. I added the () and the bold. I think 250.122(B) would apply.

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 the circular mil area of the ungrounded conductors.


Staff Note for 250.122(B)

Equipment grounding conductors are sized per Table 250.122 based on the size of the overcurrent device protecting the branch circuit or feeder. The Code section requires that if the size of the ungrounded (phase) conductors is increased to compensate for voltage drop or some other reason unrelated to ampacity(in your case the lugs), the size of equipment grounding conductor(s) must be increased proportionately.

 

[charlie b]

A #12 would violate the listed usage of the lug which, in this installation, is one component of the entire circuit, that also happens to determine the minimum conductor size.

I think I understand your reasoning. Indeed I have used similar, but not exactly the same, reasoning in other circumstances. But I cannot agree with your position.

The nature and character of a circuit is determined by the overcurrent device, not by anything else, and certainly not by the terminations at the load equipment. You have a 20 amp breaker. Therefore, you have a 20 amp circuit. The minimum size wire for a 20 amp circuit is a #12. You increased it to #6 because of lug sizes. 250.122(B) does not distinguish between one reason for upsizing and any other reason for upsizing.

I have submitted a code change proposal for 2011 on this article. My change would clarify that an "upsize" means using a conductor that is larger than the minimum that would have sufficient ampacity for the installed conditions. I have no idea if it will be accepted. But if it is, you would still lose your case for your particular example.

 

[Dennis Alwon]

Where does it say that I must use a #12 conductor? A #12 would violate the listed usage of the lug which, in this installation, is one component of the entire circuit, that also happens to determine the minimum conductor size. The minimum is #6 on a 20 amp CB, so what has been increased? A #12 conductor is not permitted, neither is a #10 or #8 so how can a #6 be considered an increase in conductor size when it's the smallest conductor permitted for this circuit?

I don't buy this Trevor. Just because a panel lugs are bigger than the wire that would be necessary to supply the given circuit is not, IMO, valid. 250.122 states:

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

IMO, increased in size means using conductors other than what is required for the circuit. If there was no relay panel then you would say the EGC must be increased but throw in a panel with large lugs and the EGC does not need to be increased. That does not make sense---:smile:

The ungrounded conductors are increased in size to accommodate the lugs, if you will. If that is the reason to run a larger conductor than the EGC must be increased.

 

[don_resqcapt19]

No matter what reason the circuit conductors have been increased for, 250.122(B) requires the EGC to be increased. With 20 amp circuits the EGC to circuit conductor size ratio is 1:1 and that must be maintained. A real bummer if you ran cable.

While I agree this is the intent of the code rule it is not exactly what the words say and Rob has a point. The rule does not specify the starting point from which the conductor is increased. It is implied and the intent of the rule that the starting point be based on the smallest permitted conductor size for the rating of the OCPD, but the rule does not say that.
There are a couple of proposals in for the 2011 code to clear this up. One proposal eliminates 250.122(B), but replaces T250.122 with one based on the size of the ungrounded conductors and not the OCPD.

 

[infinity]

While I agree this is the intent of the code rule it is not exactly what the words say and Rob has a point. The rule does not specify the starting point from which the conductor is increased. It is implied and the intent of the rule that the starting point be based on the smallest permitted conductor size for the rating of the OCPD, but the rule does not say that.
There are a couple of proposals in for the 2011 code to clear this up. One proposal eliminates 250.122(B), but replaces T250.122 with one based on the size of the ungrounded conductors and not the OCPD.

This is what I'm basing my opinion on. Nowhere in 250.122(B) am I directed to 310.16 to find the lowest conductor ampacity as a starting point. I'm all understanding about intent but I don't see how the vague wording of 250.122(B) specifies a starting point for the word increasing.

 

[iwire]

While I agree this is the intent of the code rule it is not exactly what the words say and Rob has a point. The rule does not specify the starting point from which the conductor is increased.

Don, I understood exactly what Rob was saying and what the section says. I still say 6 AWG.

The equipments lugs did not determine the wire size used the installer did. The installer could have run a few inches of 6 AWG from the lugs, used a listed connector and spliced on 12 AWG for the rest of the run to the panel.

I do agree that section could use some help but based on Robs description and the current wording I see it as 6 AWG.

 

[don_resqcapt19]

Without a starting point in the code section, the section is vague and unenforceable, at least that is my opinion. Yes I know what it means, but it doesn't say what it means, and yes it is enforced as intended, not as written. Just another example of very poor code language.

 

[M. D.]

Without a starting point in the code section, the section is vague and unenforceable, at least that is my opinion. Yes I know what it means, but it doesn't say what it means, and yes it is enforced as intended, not as written. Just another example of very poor code language.

I could not agree more ,..

How does this effect cable assemblies ,.?? I Up size from an 8 nm to a 6 nm has the grounding conductor been proportionally increased ??