Code conflicts?

A

anbm

Senior Member
Location
TX
Occupation
Designer
To reduce voltage drop, we must increase circuit wires from #12 to #6 AWG, the ground wire will be increase to #6 AWG per NEC 250.122(B) as well.
However, #6AWG conductor will be good for 65A (75 degree C conductor), and per table 250.122, #8 ground is needed not #6 as noted in NEC 250.122(B) rule above. Do these two code sections conflict?
 
IMO, you are comparing apples & oranges. I assume you are basing the #8 on the 61-100 amp ranges in Table 250.122 which is based on the size of the overcurrent device.
250.122(B) would require the #6 which trumps the Table values.
 
anbm said:
To reduce voltage drop, we must increase circuit wires from #12 to #6 AWG, the ground wire will be increase to #6 AWG per NEC 250.122(B) as well.
However, #6AWG conductor will be good for 65A (75 degree C conductor), and per table 250.122, #8 ground is needed not #6 as noted in NEC 250.122(B) rule above. Do these two code sections conflict?
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According to the 1 to 1 ratio of ungrounded to EGC the #8 is not large enough.
 
augie47 said:
IMO, you are comparing apples & oranges. I assume you are basing the #8 on the 61-100 amp ranges in Table 250.122 which is based on the size of the overcurrent device.
250.122(B) would require the #6 which trumps the Table values.
Click to expand...
Why 250.122 cannot be used in this case, that is my question. #6 is good for 60A-65A CB, which only needs #8 ground wire.
 
The Table is based on the supply overcurrent device which in this case is a 20amp requiring only a #12 however that conductor size must be adjusted by 250.122(B). The 60-65A is not relevant to that requirement.
 
In fact, I brought this up at a IAEI conference and a CMP 2 member clarified that an increase in a conductor size requires the adjustment from 250.122(B) even if the increase had nothing to do with voltage drop. For example, just because you had a larger spare wire on the truck, you would need to increase the wire type EGC size. This applies to Romex and MC as well.
 
Since #12 has a 1 to 1 ratio of hot to ground then to increase one hot conductor you need to increase it by the same proportion. Thus the equipment grounding conductor must be sized the same as the hot wire.

This change when you get into conductors larger than 10 as the larger conductors don't have a 1 to 1 ratio of hot to equipment grounding conductor.
 
Dennis Alwon said:
Since #12 has a 1 to 1 ratio of hot to ground then to increase one hot conductor you need to increase it by the same proportion. Thus the equipment grounding conductor must be sized the same as the hot wire.

This change when you get into conductors larger than 10 as the larger conductors don't have a 1 to 1 ratio of hot to equipment grounding conductor.
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Good explanation.
 
Elect117 said:
In fact, I brought this up at a IAEI conference and a CMP 2 member clarified that an increase in a conductor size requires the adjustment from 250.122(B) even if the increase had nothing to do with voltage drop. For example, just because you had a larger spare wire on the truck, you would need to increase the wire type EGC size. This applies to Romex and MC as well.
Click to expand...
Dumbest rule in the book. But it is the rule.
 
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