Table 250.102(C)(1)

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GerryB

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I am looking at some drawings for some pretty long wire runs underground in 2" pvc. I think they have oversized the grounds, for ex. A 240 volt single phase, 60 amp load at 400 feet. The drawings have 3-1/0 conductors and a #2 ground. I think you could use a #1 conductor, but according to the table, #1 or 1/0 would it not be a #6 ground?
 
For equipment grounding conductors you would use Table 250.122. An up-sized ungrounded conductor would require you to also up-size the EGC. {250.122(B)}
 
infinity said:
For equipment grounding conductors you would use Table 250.122. An up-sized ungrounded conductor would require you to also up-size the EGC. {250.122(B)}
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Thanks, figuring it out with the cir mill formula it did come out to #2 ground for a #1 ungrounded conductor opposed to a #6, if I did it correctly.
 
For a load of 60amps typically you run with #6AWG wire...but due to the voltage drop consideration they have up sized the wire size to 1/0.There is a very good explanation in NEC handbook with an example...

If you look at table 250.122 for OCD device from 60amps to 100amps EGC size is #8AWG. But as you up sized ur ungrouded conductor size from #6 to #1/0 you have to upsize ur EGC conductor as per 250.122(B).Here's a quick calculation i did...

#6AWG in kcmil=26240
#1/0AWG in kcmil=105600
Size ratio=105600/26240=4.024

#8AWG in kcmil=16510
Now you have to multiply 16510 with the size ratio to get cross sectional area of the new EGC which is
16510x4=66040kmcil.

Now look at NEC Chapter 9 table 8 66040 kcmil is lower than 66360 kcmil which is #2AWG.

Hope this helps..:):):thumbsup:
 
shoaib10 said:
For a load of 60amps typically you run with #6AWG wire...but due to the voltage drop consideration they have up sized the wire size to 1/0.There is a very good explanation in NEC handbook with an example...

If you look at table 250.122 for OCD device from 60amps to 100amps EGC size is #8AWG. But as you up sized ur ungrouded conductor size from #6 to #1/0 you have to upsize ur EGC conductor as per 250.122(B).Here's a quick calculation i did...

#6AWG in kcmil=26240
#1/0AWG in kcmil=105600
Size ratio=105600/26240=4.024

#8AWG in kcmil=16510
Now you have to multiply 16510 with the size ratio to get cross sectional area of the new EGC which is
16510x4=66040kmcil.

Now look at NEC Chapter 9 table 8 66040 kcmil is lower than 66360 kcmil which is #2AWG.

Hope this helps..:):):thumbsup:
Click to expand...

I think that you meant circular mils not kcmil.
 
shoaib10 said:
For a load of 60amps typically you run with #6AWG wire...but due to the voltage drop consideration they have up sized the wire size to 1/0.There is a very good explanation in NEC handbook with an example...

If you look at table 250.122 for OCD device from 60amps to 100amps EGC size is #8AWG. But as you up sized ur ungrouded conductor size from #6 to #1/0 you have to upsize ur EGC conductor as per 250.122(B).Here's a quick calculation i did...

#6AWG in kcmil=26240
#1/0AWG in kcmil=105600
Size ratio=105600/26240=4.024

#8AWG in kcmil=16510
Now you have to multiply 16510 with the size ratio to get cross sectional area of the new EGC which is
16510x4=66040kmcil.

Now look at NEC Chapter 9 table 8 66040 kcmil is lower than 66360 kcmil which is #2AWG.

Hope this helps..:):):thumbsup:
Click to expand...
I am at 60amps, not 100, so wouldn't that be a #10 not an 8?
 
infinity said:
60-99 amps would be a #10 copper EGC.
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Also in the same example the neutral can be reduced but not less then the egc. So the egc came out to be #4 (using #10 not #8 in the calc.) The table says for #2 you can use #8 for the grounded conductor. But since the Ungrounded conductors are larger making the egc larger the neutral cannot be less then the egc, therefore it could also be #4. Is that right?
 
GerryB said:
Also in the same example the neutral can be reduced but not less then the egc. So the egc came out to be #4 (using #10 not #8 in the calc.) The table says for #2 you can use #8 for the grounded conductor. But since the Ungrounded conductors are larger making the egc larger the neutral cannot be less then the egc, therefore it could also be #4. Is that right?
Click to expand...

As Smart$ pointed out for 61-100 amps EGC is #8 not #10..
 
Smart $ said:
21-60 amps #10 copper EGC.


61-100 amps #8 copper EGC.
Click to expand...

Yes you're correct I should have looked at T250.122 first. :roll:

Should be up to 15 amps-#14 AWG, 16-20 amps-#12 AWG, 21-60 amps-#10 AWG, 61-100 amps=#8 AWG.
 
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