Can you Parallel the ground on a single conduit???

[infinity]

Back on topic.

Picture a typical wood framed home, I run a 12/2 and a 14/2 NM from the panel to a two gang box in the kitchen, the 12/2 supplies the SABC and the 14/2 supplies the lighting, all the EGCs in this box must be connected together (250.148) so that will put a 14 and 12 AWG copper EGC in parallel. This is common and not a violation.

I agree. Even EGC's from two different panels or two different services would still be connected together in a box if they both existed there.

 

[brother]

And where in the code does it say that? :grin:

I think we need to be careful in applying that commonly held belief. Specifically, if the code explicitly says, "it shall be permissible to do A, B, and C," then I think it is, at the same time, explicitly forbidding us to do "D." In this case, 310.4 explicitly says "it shall be permitted" to parallel each "phase, polarity, neutral, or grounded" conductor. I interpret the fact that the EGC is not included in this list as an explicit declaration that the EGC shall not be paralleled.

Well, as someone pointed out, the way the code is written here, its a little unclear. To use the 'shall be permited' phrase to mean an exception and a 'prohibitive' type statement, to mean is out of context with the english language. So goes the common help belief of the NEC as a permissive document.

 

[LarryFine]

We end up with parallel EGCs all the time of all sizes, there is no NEC violation there.

Exactamundo! For example, every time we make up EGC's in a box fed by more than one cable, such as a sink-light switch and a counter receptacle in one box.

 

[JohnJ0906]

I was talking with another guy about the 'grounding being sized on the overcurrent device for the motors per NEC 250.122 (D)(1,2). The breaker is 70 amp. Instead of pulling a #8 copper based on table 250.122, it had an existing #10. He decided to pull in an ADDITIONAL #10 ground to help compensate for the size. This is one conduit, not parallel conduits.

Is it legal to do that?? It's my understanding it is not. You would have to size the single ground off of the overcurrent device, and not try to parallel them. Only thing I could find in the code was NEC 2008 250.122(F). But that even says that if you had parallel conduits then each ground pulled in each conduit would have to be sized to the over current device.

In theory I suppose if there is a fault, it would work. I know the NEC is suppose to be a permissive document, but I interpet this to not be permited.

What size are the circuit conductors? The EGC doesn't need to be larger than the hot conductors.

Seeing as this is a motor circuit, the circuit conductors may very well be smaller than usual on a 70 amp breaker.

 

[augie47]

I think I'm in agreement in stating that the Code doesn't prohibit paralleling grounding conductors for reasons Bob and Rob point out, but you can't use two "undersized" conductors to satisfy 250.122

 

[brother]

What size are the circuit conductors? The EGC doesn't need to be larger than the hot conductors.

Seeing as this is a motor circuit, the circuit conductors may very well be smaller than usual on a 70 amp breaker.

The circuit conductors are #6 copper, (I thought I made that clear in my earlier post, I'm aware that the breaker can be bigger than the wire ampacity since its the groundfault/short circuit protection) so that's what made me question this install.

I'm aware the egc doesn't have to be larger than the circuit conductors per NEC 2008 250.122(A), but in this case he should have pulled in a #8 minimum for the egc not use 2 #10's. The only time I've seen 2 grounds in a conduit is when one of them is an 'isolated' ground and other is 'dirty' or regular ground. At least that is the industry practice here. I cannot speak for other areas. Those 2 grounds being used as one, can cause serious confusion.

Never heard of or seen anyone ever try to use 2 smaller grounds to substitute for one big ground for the egc. Just wanted to be sure that there wasn't something in the code I missed.

Thanks and Happy Thanksgiving.