Grounded conductor sizing

[chuck@tracyelectricinc.co]

Art. 250.24 C2 Can someone make it clear if this article is sizing the grounded conductor off the total circular mil area of all ungrounded phase conductors in the parrallel set? or off of the total cm of one set. (assuming that they are talking about total circular mils of a single phase conductor, and not the cm total of all three phases.)
Everybody seems to have a different interpretation.

 

[don_resqcapt19]

The grounded conductor size is based on the size of the largest phase conductor in that raceway. If you have more than one conductor per phase in the raceway, then it is based on the sum of the conductors that make up the largest phase.

 

[Dennis Alwon]

I agree with Don. If you have 4 conductors per phase then add the cm of the largest 4 conductors on a phase.

 

[chuck@tracyelectricinc.co]

That is what my interpretation was, but I have an inspector looking for a larger grounded conductor, The application is 3 parallel 350 kcmil tray cables in parallel. The way I read this article I need to have a 1/0 grounded conductor per cable. With either a #2 awg Supply side bonding jumper per cable, or a single 2/0 supply side bonding jumper from my 1st disconnecting means, back to the transformer frame.

 

[don_resqcapt19]

Are these service conductors or feeders? Are we talking about the neutral (grounded) conductor or an equipment grounding conductor or a supply side bonding jumper?

 

[texie]

That is what my interpretation was, but I have an inspector looking for a larger grounded conductor, The application is 3 parallel 350 kcmil tray cables in parallel. The way I read this article I need to have a 1/0 grounded conductor per cable. With either a #2 awg Supply side bonding jumper per cable, or a single 2/0 supply side bonding jumper from my 1st disconnecting means, back to the transformer frame.

250.24(C)(2) would require a conductor from Table 250.66 based on 350 X 3 = 1050 KCM. That would be a 2/0. I'm afraid the inspector is right (I'm assuming this is all copper).

 

[texie]

Are these service conductors or feeders?

Good question. You see from my post I was assuming service conductors, but now I'm not so sure now that I reread it.

 

[chuck@tracyelectricinc.co]

This is a seperately derived service in an industrial building. Hitting a transformer with 480 vac 3 phase, and transforming voltage down to 400 vac 3 phase. It is not an auto transformer.

 

[chuck@tracyelectricinc.co]

This installation currently has a 3/0 copper grounded conductor per each of the three tray cables, the inspector is looking for a 4/0.

 

[chuck@tracyelectricinc.co]

Also, there is no neutral load. Just trying to make sure I am understanding the article correctly, the change to the 2011 code was "in the raceway" It does not mention cables. My interpretation is that a tray cable is it's own raceway. But it does not say raceway, or cable. and it does not say raceway/s. Which would change the meaning entirely. Any thoughts?

 

[don_resqcapt19]

Is there an "XO" terminal on the transformer secondary? If so, is it used and is it bonded to a grounding electrode system?

 

[don_resqcapt19]

Also, there is no neutral load. Just trying to make sure I am understanding the article correctly, the change to the 2011 code was "in the raceway" It does not mention cables. My interpretation is that a tray cable is it's own raceway. But it does not say raceway, or cable. and it does not say raceway/s. Which would change the meaning entirely. Any thoughts?

I don't think 250.24 even applies to this installation, however the wording in 250.30(A)(3)(b) is much the same.

 

[chuck@tracyelectricinc.co]

Thanks for the help.

Thanks for the help.

Thanks for the help, got back to my handbook, and realized I should have been in article 250.30 instead of article 250.24.

 

[chuck@tracyelectricinc.co]

Yes, the XO terminal is bonded.

 

[chuck@tracyelectricinc.co]

Back to the origional question new article

Back to the origional question new article

The grounded conductor installed in parallel, for the grounded conductor in each raceway, is it to be sized for "the total circular mil area of the parallel dervied ungrounded conductors in the raceway"? (singular) or all the raceways in the parallel set? And is a tray cable, in the intention of this article to be considered like a raceway?

 

[Dennis Alwon]

The grounded conductor installed in parallel, for the grounded conductor in each raceway, is it to be sized for "the total circular mil area of the parallel dervied ungrounded conductors in the raceway"? (singular) or all the raceways in the parallel set? And is a tray cable, in the intention of this article to be considered like a raceway?

Although a tray cable is not a raceway by definition I would think that that is the intent of the article