250.122 (B)

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peter d

peter d

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A few issues have me confused. :confused:

Part of 250.122(B) says that "EGC's ... shall be increased in size proportionally according to the circular mil area... "

Does the code provide any guidelines, tables or formulas to accomplish this?

I tried calculating some ratios from Table 250.122 (comparing EGC size to ungrounded size) but couldn't come up with anything that made sense.

Are there any rules of thumb to size the EGC for coductors increased in size for voltage drop?

Here is a situation that I ran into the other day that got me thinking about this. Parking lot lights on 30 amp, 240 volt circuit. Contractor ran #6 ungrounded with #10 ground. Is this compliant?

Unrelated question: The "taps" run up the poles to said lights were #10. How do we determine the size of these? It appeared to me that #12 or #14 could have been acceptable by 240.5(B)(2), but I am making the assumption that these "taps" are fixture wire. Right/wrong?
 
Re: 250.122 (B)

Parking lot lights on 30 amp, 240 volt circuit. Contractor ran #6 ungrounded with #10 ground. Is this compliant?
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No, that is a violation of 250.12(B). For circuits protected by devices 30 amps of less this section is very easy. The equipment grounding conductor must be the same size as the ungrounded conductors. When you are working with OCPDs larger than 30 amps you have to do some calculations. Say for an example you are installing a 40 amp circuit that would normally use #8, but because of the distance (or any other reason) you install #4. First go to chapter 9 and find the circular mil area of #10(normally required EGC size for 40 amp circuit), #8 and #4. Devide the area of the #4 by the area of the #8. Now take the result and multiply the area of the #10 by it. This is the minimum size of your equipment grounding conductor. Sorry, I don't have time to put any real numbers to this process right now.
Don
 
Re: 250.122 (B)

If you have access to the 2002 NEC Handbook the explanatory print on page 216 mayfill in the calculations that Don discussed.

Charlie
 
Re: 250.122 (B)

Thanks Don.

So in the parking lot lights I encountered the other day, the EGC's should have been a #6.

Basically, 30 amps and under, EGC size = ungrounded size? If we had to use #4 on this 30 amp circuit, the EGC's would have to be #4 as well?

Also, the method you described, is that in the NEC?

Edited to clarify

[ October 21, 2004, 02:57 PM: Message edited by: peter d ]
 
Re: 250.122 (B)

Yes. For 15,20 or 30 amp circuits the EGC must be the same size as the ungrounded conductors.

For example:

A 20 amp circuit would normally require a #12 ungrounded conductor, but due to voltage drop we install #8. We go to table 8 and find that a #12 has a circular mil of 6530. We increased to a #8, which is 16510. This is an increase of 2.52 times the size of the #12. We then go to table 250.122 and find that the EGC required for a 20 amp OCPD is #12, but we must increase the circular mil of the #12 by 2.52 and in doing so we come up with a #8 required.

Because of this there is no math required for 15, 20 or amp. Once we get above 30 amps we have to do the math.
 
Re: 250.122 (B)

As I think about this some more, I realize that many electricians blindly follow Table 250.122 without any regard to 250.122(B).
 
Re: 250.122 (B)

Originally posted by peter d:
As I think about this some more, I realize that many electricians blindly follow Table 250.122 without any regard to 250.122(B).
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Or any regard to the Note to the Table as well.
 
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