Question about grounding.

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Dennisc

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A 15A two-wire circuit, a 20A two-wire circuit, and a 40A two-wire circuit is installed in a nonmetallic rigid conduit. How many equipment grounding conductors would be required? What size(s) would be required?

Thanks Dennis
 

Dennisc

Member
Yes this is definitely a homework problem. I cannot find table '250.122(C" anywhere in my textbook. I did find a spot where it said that on 15,20, and 30A you must use the same size ground as conductor. So I'm guessing I could undersize the ground for the 40A circuit if I had the table and thats the size I would need. I would guess that I would only need one ground for all 3 of these circuits.
 

480sparky

Senior Member
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Iowegia
Yes this is definitely a homework problem. I cannot find table '250.122(C" anywhere in my textbook. I did find a spot where it said that on 15,20, and 30A you must use the same size ground as conductor. So I'm guessing I could undersize the ground for the 40A circuit if I had the table and thats the size I would need. I would guess that I would only need one ground for all 3 of these circuits.

T250.122(C) is in the NEC, not your textbook.
 

Dennisc

Member
Yes I know its in the NEC, but normally they will have the table's needed copied in the textbook.

Thanks Dennis
 

roger

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Yes this is definitely a homework problem. I cannot find table '250.122(C" anywhere in my textbook. I did find a spot where it said that on 15,20, and 30A you must use the same size ground as conductor. So I'm guessing I could undersize the ground for the 40A circuit if I had the table and thats the size I would need. I would guess that I would only need one ground for all 3 of these circuits.

Dennis, here is a hint, 250.122(C) is not a table.

Roger
 

charlie b

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I did find a spot where it said that on 15,20, and 30A you must use the same size ground as conductor.
That is not true. The size of the Equipment Grounding Conductor (i.e., the minimum allowable size) is based on the rating of the overcurrent protection device (OCPD). NEC Table 250.122 lists various OCPD ratings and gives the minimum EGC size. For 15 amp, the size is #14; for 20 amp it is #12, and for 30 amp it is #10. These values are for copper conductors; aluminum conductors must be larger.

I would guess that I would only need one ground for all 3 of these circuits.
That is correct, but it would be better not to guess. The text of paragraph 250.122(C) tells you exactly that. It also says that the size must be based on the largest OCPD protecting any of the circuits in the same conduit.

So I'm guessing I could undersize the ground for the 40A circuit if I had the table and that?s the size I would need.
That would be a bad guess. If you have a 15, a 20, and a 40 in the same conduit, you can use a single EGC, if you size that EGC for the 40 amp circuit.


If you look in the FAQ section of this forum, you will find a link to a free on-line version of the NEC. It is not a very convenient version, as it cannot be word-searched, nor can its text be copied and pasted, nor can it be printed. But you can look up the article we have been talking about, and see for yourself what we have been saying.

Good luck.
 

Dennisc

Member
Thank you very much for the helpful info. I will definitely be checking out the online NEC. I never had any idea that was on this site.

Thanks Dennis
 

Dennisc

Member
If you look in the FAQ section of this forum, you will find a link to a free on-line version of the NEC. It is not a very convenient version, as it cannot be word-searched, nor can its text be copied and pasted, nor can it be printed. But you can look up the article we have been talking about, and see for yourself what we have been saying.

I'm not having any luck finding this. Any ideas on this link?

Thanks Dennis
 

infinity

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Location
New Jersey
Occupation
Journeyman Electrician
Yes this is definitely a homework problem. I cannot find table '250.122(C" anywhere in my textbook. I did find a spot where it said that on 15,20, and 30A you must use the same size ground as conductor.

That is not true. The size of the Equipment Grounding Conductor (i.e., the minimum allowable size) is based on the rating of the overcurrent protection device (OCPD). NEC Table 250.122 lists various OCPD ratings and gives the minimum EGC size. For 15 amp, the size is #14; for 20 amp it is #12, and for 30 amp it is #10.

Actually it is true that for 15,20 and 30 amp circuits the EGC is the same size as the phase conductors.
 

charlie b

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Lockport, IL
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Actually it is true that for 15,20 and 30 amp circuits the EGC is the same size as the phase conductors.
It does not have to be the same size. It just can't (generally) be smaller. The (nobody ever does this but it is legal anyway) exception is that if the ungrounded conductor is aluminum, and if the EGC is copper, then the EGC can indeed be smaller than the ungrounded conductor. :D
 
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