Ground Pig Tails

[Hawkeye Gabe]

I have a situation with the ground pig tails. We are using #12awg x 10” ground pig tails in our fixture j boxes. We pulled #10awg throughout lighting system (parking garage) for distance.
Inspector is saying the ground to the box needs to be the same size as run in conduit.
I can’t find anywhere that tells me that’s right
or wrong. I was thinking this could be a UL tested assembly with UL listed ground screws but can’t find that either. Can anyone help me out with this so we don’t have to drop 800 fixtures and install #10 ground?
Thank you

 

[roger]

Read through 250.122, not just the Table.

Roger

 

[infinity]

Can anyone help me out with this so we don’t have to drop 800 fixtures and install #10 ground?
Thank you

Are the fixtures mounted to the junction boxes? Hate to say it but ouch this one is going to hurt.

 

[480sparky]

Especially (B).

 

[flashlight]

Ouch! Sorry, Hawkeye, B pretty much spells it out.

Doesn't make sense to me considering OCPDs at 20A, but I'm sure someone here will explain reasoning.

 

[texie]

Ouch indeed. Technically a violation but in my view the the code does not directly address this but should as this short pigtail sized to 250.122 from a physics standpoint is fine. It is no different than a long run that has large conductors for voltage drop and then splicing a standard size conductor at each end.

 

[LarryFine]

It is no different than a long run that has large conductors for voltage drop and then splicing a standard size conductor at each end.

I see this, and suggest making the point to the inspector's supervisor if necessary.

 

[roger]

Ouch indeed. Technically a violation but in my view the the code does not directly address this but should as this short pigtail sized to 250.122 from a physics standpoint is fine. It is no different than a long run that has large conductors for voltage drop and then splicing a standard size conductor at each end.

And I whole heartedly agree. If the inspector forced this change he is being unreasonable and a jerk.

Roger

 

[flashlight]

Ouch indeed. Technically a violation but in my view the the code does not directly address this but should as this short pigtail sized to 250.122 from a physics standpoint is fine. It is no different than a long run that has large conductors for voltage drop and then splicing a standard size conductor at each end.

What Texie said

 

[texie]

This is one of those areas that the inspector has the letter of the code on his side but the physics do not support it. If this was in my jurisdiction I would have no issue approving it. Sounds like a good code change to recognize the physics of the matter.

 

[zbang]

Inspector is saying the ground to the box needs to be the same size as run in conduit.

Are you using the conduit system as the EGC or was a separate one pulled? (I kind of assume the first, but it's not clear.)

I also think the inspector is being unreasonable.

 

[480sparky]

Ouch! Sorry, Hawkeye, B pretty much spells it out.

Doesn't make sense to me considering OCPDs at 20A, but I'm sure someone here will explain reasoning.

Conductors need to carry any fault current. If you have a section of conductor that is smaller, it's current-carrying capacity is reduced, and the net result is longer fault current flow time.

 

[curt swartz]

Conductors need to carry any fault current. If you have a section of conductor that is smaller, it's current-carrying capacity is reduced, and the net result is longer fault current flow time.

I don't see how 10" of #12 bonding a J-Box is going to have much effect on fault clearing time.

 

[480sparky]

I don't see how 10" of #12 bonding a J-Box is going to have much effect on fault clearing time.

How many thousands of amps are going to be coursing through the circuit? How much heat will be generated with a few more cycles allowed to pass?

 

[texie]

Conductors need to carry any fault current. If you have a section of conductor that is smaller, it's current-carrying capacity is reduced, and the net result is longer fault current flow time.

OK, so what if the OP just ignored voltage drop and simply used #12 conductors for the circuit as would be allowed for this 20 amp branch circuit. The 250.122 would then allow the the EGC for the entire circuit to be #12, including the pigtails. So now you would have hundreds of feet of #12 as the EGC path. Which do you think has the least resistance, 100 feet of #12 or 100 feet of #10 with 12 inches of #12 spliced onto the end?

 

[bwat]

How many thousands of amps are going to be coursing through the circuit? How much heat will be generated with a few more cycles allowed to pass?

Do you actually think the 10” of #12 would make a noticeable difference?

Let’s say it’s 200 feet from source, so 400 feet round trip to the box, and 1 foot pig tails to make it easy. 400 ft of #10 plus 1 ft of #12. Compare the impedance of that to 401 ft of #10. I’d bet the difference is insanely small. Does somebody mind crunching this real quick?

And for longer distances, the difference gets smaller (less of an issue). And for short distances, the reason behind the code rule largely doesn’t make sense. It would clear just fine if the whole thing was #12 at short distances, so a combination of 10 and 12 would be even better.

And this is all for just bolted faults. In reality, that nature of the fault is going to have a huge impact on actual clearing time.

 

[LarryFine]

Suppose the conduit was the only EGC and the circuit conductors were #10. What size would the pigtails need to be?

 

[texie]

Suppose the conduit was the only EGC and the circuit conductors were #10. What size would the pigtails need to be?

Good question. It further illustrates the poor wording of this area of the code and the lack of recognition of the obvious laws of physics. This would be like the code requiring a circuit that is upsized for VD to be complete from end to end using the upsized conductors which would be absurd.

 

[LarryFine]

This would be like the code requiring a circuit that is upsized for VD to be complete from end to end using the upsized conductors which would be absurd.

The code says it's for the section(s) that are upsized, which wouldn't apply to the fixture pigtails.

 

[texie]

The code says it's for the section(s) that are upsized, which wouldn't apply to the fixture pigtails.

Good point.