NEC 2014 section 250.122

hhsting

Senior Member
I have more than three current carrying conductors in conduit fed from 50A bkr and 20A bkr. There are 4#2 phase conductors from 50A bkr and 4#8 phase conductors from 20A bkr.

The phase conductors have been enlarged due to voltage drop. Since all phase conductors are in one conduit one #6 awg EGC has been provided.

I said the EGC size of #6 is not in compliance with NEC 2014 section 250.122(B) however response came back saying it is in compliance with 250.122(C) and based on 50A bkr. 250.122(B) does not apply

No where in NEC 2014 section 250.122 it says to comply with 250.122(B) and 250.122(C). So its not clear and I am not convinced that 250.122(B) does not apply since 250.122(C) is taken into account.

Wanted to know your thoughts is #6 EGC not in compliance with 250.122(B) or 250.122(B) does not apply since 250.122(C) is taken into account?
 

tom baker

First Chief Moderator
Staff member
250.122 has been much changed over the years. In the 2017 NEC, 250.122 B, if you could look at it, answers your question. B and C are separate sections.
Next question?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
It seems pretty clear to me that in the 2014 edition anyway, that 250.122(C) stands alone and thus the smallest size EGC would be #10 copper or #8 aluminum.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
250.122(B) Where ungrounded conductors are increased in size....... EGC shall be increased proportionally.
Item left out of your opening statement that would alter any determination immediately is you didn't state what is the conductors type?
But If using THHN you have theoretically increased by 3 sizes using adjustment factor Table 310.15(B)(3)(a). Thus the EGC needs to increase by 3 bringing that to a #4 minimum size Table 250.122.
250.122(C) just says that if you have different size conductors in a raceway, EGC to be sized based on the largest conductor.
 

hhsting

Senior Member
250.122(B) Where ungrounded conductors are increased in size....... EGC shall be increased proportionally.
Item left out of your opening statement that would alter any determination immediately is you didn't state what is the conductors type?
But If using THHN you have theoretically increased by 3 sizes using adjustment factor Table 310.15(B)(3)(a). Thus the EGC needs to increase by 3 bringing that to a #4 minimum size Table 250.122.
250.122(C) just says that if you have different size conductors in a raceway, EGC to be sized based on the largest conductor.
Phase Size was increased due to voltage drop. I did calcs and would imagine then #2 would be the smallest not #4 according to 250.122(B)?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Phase Size was increased due to voltage drop. I did calcs and would imagine then #2 would be the smallest not #4 according to 250.122(B)?
Can we see the calculation? You need to find the proportional change from #8 to #2 and apply that to the EGC.
 

hhsting

Senior Member
Can we see the calculation? You need to find the proportional change from #8 to #2 and apply that to the EGC.


50A bkr needs #8 copper min phase and #10 egc min. However whats provided is #2 phase.
#2 is 66,361 awg, #8 is 16,507 awg, #10 is 10,382 awg

(66,361)/(16,507)*(10,382) =41,737 awg which is #3. Right #3 is what i got. How you got #4? Also would one #3 EGC be ok or need another for 20A bkr which would be #8?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
From Chapter 9, Table 8:
#10 AWG=10380 Circular Mils
#8 AWG=16510 CM
#2 AWG=66360 CM
66360/16510*10380=41721
#4 AWG=41740
 
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