Nec 250.122(g)

[erickench]

I read the above NEC section and I see a problem with the language. It states:

Equipment grounding conductors run with feeder taps shall not be smaller than shown in Table 250.122 based on the rating of the overcurrent device ahead of the feeder but shall not be required to be larger than the tap conductors.

Let us assume a 10 foot tap with the feeder protected at 150A. According to NEC 240 10 ft taps can have an ampacity as low as 1/10 of the rating of the OCPD which in this example would be 15A. Here's the problem if you size the EGC to 15A ampacity it would violate the first part of the above stated rule where it state's that the EGC cannot be smaller than shown in NEC Table 250.122. So why does it say that the EGC is not required to be larger than the tap conductors? It would certainly have to be larger in this case.

 

[augie47]

why would the equipment ground be required to carry more current than the phase conductor ?

 

[kwired]

if "but shall not be required to be larger than the tap conductors" were written as an exception would this make more sense? because that is how I see it and I don't see the need for an exception the word "but" serves that purpose in this case.

 

[TT009]

Which article are you following for the 1/10?

 

[erickench]

Which article are you following for the 1/10?

Is'nt it the general rule that a 10 ft tap is usually sized at a minimum of 1/10 the rating of the OCPD?

 

[erickench]

why would the equipment ground be required to carry more current than the phase conductor ?

The question is about the tap conductor which can be sized as small as 1/10 of the same OCPD which is being used to size the EGC. The EGC would be larger than the tap because of the larger rating of the feeder OCPD. Unless the tap were the same size as the feeder.

 

[infinity]

Is'nt it the general rule that a 10 ft tap is usually sized at a minimum of 1/10 the rating of the OCPD?

Yes, for the 10 foot tap rule in 240.21(B)(1). Even at 10% of the ampacity of the OCPD ahead of the feeder the EGC should still be large enough to open the OCPD ahead of the tap.

 

[augie47]

The question is about the tap conductor which can be sized as small as 1/10 of the same OCPD which is being used to size the EGC. The EGC would be larger than the tap because of the larger rating of the feeder OCPD. Unless the tap were the same size as the feeder.

I don't think that's what the Code says.

 

[erickench]

Yes, for the 10 foot tap rule in 240.21(B)(1). Even at 10% of the ampacity of the OCPD ahead of the feeder the EGC should still be large enough to open the OCPD ahead of the tap.

Agreed. But that second part of the rule: "but shall not be required to be larger than the tap conductors" is confusing things. How many cases do you know of where the EGC is not larger than the tap? And if the tap were the same size as the feeder would it still be considered a tap?

 

[augie47]

Agreed. But that second part of the rule: "but shall not be required to be larger than the tap conductors" is confusing things.

so we ignore it ?

How many cases do you know of where the EGC is not larger than the tap?

most

And if the tap were the same size as the feeder would it still be considered a tap?

No

I don't particularly like the wording, but as I mentioned earlier, why should the grounding conductor need to be larger than the phase conductors.
Where would the higher current originate ? The phase conductor has to deliver the current.
I might never install a small grounding conductor on the 10% tap rule, but I can't see it as a violation.

 

[erickench]

Okay. If we go back to our previous example of a 150A feeder the EGC would be sized at No.6 AWG in accordance with NEC Table 250.122. Now at 10% the tap is sized at No.14 AWG. If we increase size of the tap beyond No.6 AWG up to No. 1/0 AWG then the EGC could still remain at No.6 AWG as the minimum size.

 

[don_resqcapt19]

Okay. If we go back to our previous example of a 150A feeder the EGC would be sized at No.6 AWG in accordance with NEC Table 250.122. Now at 10% the tap is sized at No.14 AWG. If we increase size of the tap beyond No.6 AWG up to No. 1/0 AWG then the EGC could still remain at No.6 AWG as the minimum size.

If the tap rule permits the use of a #14 tap conductor, then the largest EGC required for the tap circuit is a #14.

 

[iwire]

If the tap rule permits the use of a #14 tap conductor, then the largest EGC required for the tap circuit is a #14.

I agree with Don.

 

[erickench]

But that's just the point. The rule conflict's with itself. In one case the EGC is sized at a minimum according to NEC 250.122 and in the other it state's that it is not required to be sized larger than the tap conductor.

 

[augie47]

which makes it different from hundreds of other Code requirements where something must fit requirement "A" or "B" in what way ?

 

[iwire]

But that's just the point. The rule conflict's with itself. In one case the EGC is sized at a minimum according to NEC 250.122 and in the other it state's that it is not required to be sized larger than the tap conductor.

I do not see it as a conflict anymore then Table 250.66 is in conflict with 250.66(A), (B) or (C).

The table is the general rule and the code sections make changes to it for specific circumstances.

 

[don_resqcapt19]

But that's just the point. The rule conflict's with itself. In one case the EGC is sized at a minimum according to NEC 250.122 and in the other it state's that it is not required to be sized larger than the tap conductor.

The second part acts as an exception to the first part. There is no conflict.

250.122 Size of Equipment Grounding Conductors.
(A) General. Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122, but in no case shall they be required to be larger than the circuit conductors supplying the equipment. Where a cable tray, a raceway, or a cable armor or sheath is used as the equipment grounding conductor, as provided in 250.118 and 250.134(A), it shall comply with 250.4(A)(5) or (B)(4).

 

[erickench]

Well if I had written the rule here's how I would state it:

Equipment grounding conductors run with feeder taps shall not be larger than the tap conductors and in no case shall they be larger than the equipment grounding conductors run with the feeder.


Maybe I'll make a proposal.

 

[iwire]

Well if I had written the rule here's how I would state it:

Equipment grounding conductors run with feeder taps shall not be larger than the tap conductors and in no case shall they be larger than the equipment grounding conductors run with the feeder.


Maybe I'll make a proposal.

What is the minimum size required by your wording?

 

[erickench]

That would be determined by the EGC for the feeder which is sized in accordance with NEC Table 250.122. It does'nt make sense for the tap EGC to be larger than the feeder EGC. Besides 250.122 cannot be used to determine a minimum size for the tap because it would larger than the tap conductor itself in some cases. See the example I have given.