250.122(B) & 250.122(C) contradiction

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mdshunk

mdshunk

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When I have a PVC conduit and junction boxes that all contain 20 amp circuits, but some of them have been upsized to overcome voltage drop, how do I size the EGC? Some of the conductors are #4, which would seem to require #4 ground in accordance with 250.122(B) which says "shall be increased in size...". Now, since there are multiple conductors in this conduit and boxes (all 20 amp), 250.122(C) seems to indicate only a #12 ground. It says, " shall be sized for the largest overcurrent device.". How do I size when both articles apply and both say " shall be"?? Other than one article requireing a larger EGC, there doesn't seem to be any "tie breaking" article in the code that would require me to pick the larger one. Obviously, good sense would cause me to pick the larger one, but the code doesn't seem to make that choice for me clear.
 
Re: 250.122(B) & 250.122(C) contradiction

You would need to use a #4 AWG equipment grounding conductor for this 20 amp circuit. When increasing circuit conductor size you must increase the GEC also proportionately. Assuming that your 20 amp circuit normally would require #12 circuit conductors and a #12 EGC the proportional increase would be 1 to 1. Therefore for every wire size that you've increased the circuit conductors the EGC would increase by the same size.
 
Re: 250.122(B) & 250.122(C) contradiction

I appreciate that response, infinity, but I might have not made myself clear. There are multiple 20 amp circuits in the conduit and associated junction boxes, not just the one that was upsized. If it was just one upsized circuit, the EGC would be as you stated. There are multiple circuits, come upsized and some not, therefore I see 250.122(B) and (C) both applying.
 
Re: 250.122(B) & 250.122(C) contradiction

You would only need one #4 EGC for all of your circuits. The other smaller EGC's could be spliced to it. The EGC is sized for the largest overcurrent device and as you've stated must be increased in size if the circuit conductors are increased in size as well. Since you've chosen to use #4 for the circuit conductors than a #4 EGC is required for that circuit. It may also be used for all of the other circuits since only one EGC is required.
 
Re: 250.122(B) & 250.122(C) contradiction

Originally posted by infinity:
You would only need one #4 EGC for all of your circuits.
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That's what I would do, but the mandate to choose the size required in part(B) over the size required in (C) doesn't seem to be there. Both sections say "shall be sized...". It seems intuitive that when two sections seem to conflict, that the larger size should be chosen. The mandate to choose the larger one doesn't seem to appear in the code.
 
Re: 250.122(B) & 250.122(C) contradiction

The mandate to choose the larger one doesn't seem to appear in the code.
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The mandate is to use a #4 EGC with the #4 branch circuit conductors since you have increased the size of branch circuit conductors. What you use as a EGC for the other circuits is your choice as long as it complies with 250.122. It could be the same #4 but doesn't have to be.
 
Re: 250.122(B) & 250.122(C) contradiction

...The mandate is to use a #4 EGC with the #4 branch circuit conductors since you have increased the size of branch circuit conductors....
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I have to disagree with you on this. IF I were to install a #4 AWG conductor, with a 80 Amp overcurrent protection, I would only be required to install a #8 EGC, not a #4.

I can't believe that I would be required to use a larger EGC than would otherwise be needed on a normal sized circuit, much less than with smaller overcurrent protection.
 
Re: 250.122(B) & 250.122(C) contradiction

Originally posted by kbsparky:
I can't believe that I would be required to use a larger EGC than would otherwise be needed on a normal sized circuit, much less than with smaller overcurrent protection.
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KB... just take a look at 250.122(B). This is a "quirk" that only pops up when upsizing conductors for voltage drop.
 
Re: 250.122(B) & 250.122(C) contradiction

As stated in my original post since the branch circuit conductors and the EGC are the same size they would have to be increased proportionately as stated in 250.122(B). They are both required by Table 250.122 to be #12 AWG for a 20 amp circuit. Since this proportion is 1 to 1 they would each have to increase size for size. Increasing the branch circuit conductors to #4 requires the EGC to be increased to #4 as well.
 
Re: 250.122(B) & 250.122(C) contradiction

I agree that if you upsize your conductors you must upsize your equipment ground. I had a conversation with an inspector about grounds and multiple circuits in a conduit.

Example: Conduit (PVC) with 3 20-amp circuits (240-volt) feeding exterior lights.

This inspector said I would have to install 3 20-amp rated equipment ground conductors, 1 for each circuit since all three could fault at the same time. I did not agree with that statement, but had more important things to do than argue this point.

Later I thought about this some more and considered it a valid point. In conduits with multiple circuits, I now pull an equipment ground large enough to handle the sum of overcurrent devices (highest on 1 phase). If I upsize for voltage drop, I upsize the ground as required by the NEC.
 
Re: 250.122(B) & 250.122(C) contradiction

kbsparky, the reason for 250.122(B) is that when ungrounded conductors are upsized for voltage drop, this creates less resistance and thus a higher available fault current that the EGC must be able to safely carry until the OCPD operates. If the EGC were not upsized in relation to the ungrounded conductors a ground fault could burn up the EGC and the OCPD may not open in time. :eek:
 
Re: 250.122(B) & 250.122(C) contradiction

To answer the original post, When there are multiple code rules that affect an installation, you must follow all of them. The equipment grounding size required is a minimum selection, therefore selecting a #4 cu awg for your installation is the easy and correct answer. Is it at least a #12, Yes, and is it at least a #4, yes. Thus it is the one you shall use. Also remember the increase of an equipment grounding conductor is not just for voltage drop, but for any time you increase the size of the ungrounded conductors.

Fred Bender
 
Re: 250.122(B) & 250.122(C) contradiction

This inspector said I would have to install 3 20-amp rated equipment ground conductors, 1 for each circuit since all three could fault at the same time. I did not agree with that statement, but had more important things to do than argue this point.

Later I thought about this some more and considered it a valid point. In conduits with multiple circuits, I now pull an equipment ground large enough to handle the sum of overcurrent devices (highest on 1 phase). If I upsize for voltage drop, I upsize the ground as required by the NEC.


Thats all well and good but not required! You only need one equipment grounding conductor sized for the largest overcurrent device protecting the conductors in the raceway 250.122 C. If you look in the handbook (2005) there is an example given for three 3-phase circuits in the same raceway protected at 30, 60, and 100A and the single equipment grounding conductor is sized as a 8 AWG for the 100A overcurent device.

Edited because I didn't read!

[ June 15, 2005, 02:05 PM: Message edited by: guesseral ]
 
Re: 250.122(B) & 250.122(C) contradiction

This inspector said I would have to install 3 20-amp rated equipment ground conductors, 1 for each circuit since all three could fault at the same time.
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He is wrong and in the end it's costing you money. Inspectors can not make up their own rules. The book says that only one is required regardless of his argument.
 
Re: 250.122(B) & 250.122(C) contradiction

David Z- Another reason EGC?s are increased when circuit conductors are upsized for V drop is to minimize dangerous voltages to ground at faulted equipment. Any V drop in the EGC will be impressed on the equipment during the fault.

If the power circuit is long enough to create excessive voltage drop in the power conductors, the EGC in the same circuit will also have a higher voltage drop.

Someone touching a faulted motor?s case while standing on wet ground will feel the shock voltage created by the EGC voltage drop. (That's why we bond motor frames to local steel.)

Of course, as you stated, excessive V drop in the EGC also reduces the fault current, increasing the CB or fuse clearing time.
 
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