I recently pulled #6 conductors to a VFD protected bya 50A ocp. the plans called for 3 #8's w/#10 ground. i ran out of #8 and had #6 available so i used it. the inspector told me that since I used a larger conductor I now needed to pull a #8 ground with the #6. I am familiar with 250.122(b) in the 2002 NEC but this increased conductor size is not to eliminate voltage drop or anything else, just what I had on the truck. i am not really trying to prove anyone wrong, I am simply curious about the meaning behind the article and maybe some examples of why, under these circumstances, i would need to pull a bigger ground. thanks , justin
increased in size?
- Thread starter justin
- Start date
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- Location
- Illinois
- Occupation
- retired electrician
Re: increased in size?
Because what you told the inspector was often used as a way around the rule in the '99 code that only required an increase in the size of the EGC if the circuit conductors were increased to reduce the voltage drop. Also if you increase the size of the circuit conductors, you have reduced the impedance of the circuit and there is more current available at the fault location, so a larger EGC will clear the fault faster.
Don
Because what you told the inspector was often used as a way around the rule in the '99 code that only required an increase in the size of the EGC if the circuit conductors were increased to reduce the voltage drop. Also if you increase the size of the circuit conductors, you have reduced the impedance of the circuit and there is more current available at the fault location, so a larger EGC will clear the fault faster.
Don
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
Re: increased in size?
Hi Justin. The intent is that if you are increasing the conductors due to voltage drop, you are in reality trying to lower the impedance of the circuit because it is too much. You must also do this to the EGC so that its impedance isn't so high that the fault current won't initiate the OCPD.
The 99 version of 250.122(B) said only for voltage drop, but the 2002 says for any reason. If I were your inspector and I heard your side of the stroy, I would let it go, but thats just me.
Hi Justin. The intent is that if you are increasing the conductors due to voltage drop, you are in reality trying to lower the impedance of the circuit because it is too much. You must also do this to the EGC so that its impedance isn't so high that the fault current won't initiate the OCPD.
The 99 version of 250.122(B) said only for voltage drop, but the 2002 says for any reason. If I were your inspector and I heard your side of the stroy, I would let it go, but thats just me.
curt swartz
Senior Member
- Location
- San Jose, CA
- Occupation
- Electrical Contractor
Re: increased in size?
I understand the NEC and the reason the EGC should be increased when increasing the phase conductors but have a little problem agreeing with the inspectors call here. Many terminals on 50 amp devices are only rated for 60C conductors so #6 is used with a #10 EGC but if your terminals are rated for 75C and you use the same #6 conductors you are required to increase the size of the EGC? Does this mean that #6 NM cable can not be used on 75C terminals?
I understand the NEC and the reason the EGC should be increased when increasing the phase conductors but have a little problem agreeing with the inspectors call here. Many terminals on 50 amp devices are only rated for 60C conductors so #6 is used with a #10 EGC but if your terminals are rated for 75C and you use the same #6 conductors you are required to increase the size of the EGC? Does this mean that #6 NM cable can not be used on 75C terminals?
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: increased in size?
I don?t think the terminals have anything to do with the issue. Nor does the cable's insulation system. The only thing that matters is the size of the phase conductors.
I don?t think the terminals have anything to do with the issue. Nor does the cable's insulation system. The only thing that matters is the size of the phase conductors.
curt swartz
Senior Member
- Location
- San Jose, CA
- Occupation
- Electrical Contractor
Re: increased in size?
Charlie,
I agree with you but normally a 50 amp circuit would require #6 phase conductors (60C column of 310.16) and a #10 EGC (250.122). Isn?t this what was installed? Now if the terminals were rated for 75C allowing the use of #8 phase conductors but the installer still used #6 why should the EGC have to be increased? If I replace an old 50 amp 60C rated circuit breaker feeding #6 conductors with a new circuit breaker that happens to be rated for 75C conductors am I required to replace the #6?s with #8?s or replace the #10 EGC with a #8? I don?t feel that the phase conductors were oversized in the original posters installation.
Charlie,
I agree with you but normally a 50 amp circuit would require #6 phase conductors (60C column of 310.16) and a #10 EGC (250.122). Isn?t this what was installed? Now if the terminals were rated for 75C allowing the use of #8 phase conductors but the installer still used #6 why should the EGC have to be increased? If I replace an old 50 amp 60C rated circuit breaker feeding #6 conductors with a new circuit breaker that happens to be rated for 75C conductors am I required to replace the #6?s with #8?s or replace the #10 EGC with a #8? I don?t feel that the phase conductors were oversized in the original posters installation.
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