We are using 8/2C MC cable for a 120V circuit protected by a 20A breaker. No. 8 is being used to compensate for voltage drop. The factory supplied eq. ground size is No. 10. The manufacturer states that the cable is in compliance with UL 1569 which allows reduced eq. grounds in MC cable. The inspecting authority is challenging the eq. ground size citing NEC 250.122.B as requiring the eq. ground to be increased in size proportional to the ungrounded conductors, therefore the eq. ground should be a No. 8. We disagree. Thoughts?
Equipment Ground Size in MC Cable
- Thread starter Jdm727
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peter d
Senior Member
- Location
- New England
Re: Equipment Ground Size in MC Cable
The inspector is right.
The inspector is right.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Re: Equipment Ground Size in MC Cable
Is the point that, since #12 has a full-size ground, any upsized circuit conductors require the GEC be full-size, without limitation?
But "proportionally increased" does not necessarily mean to the same size as the circuit conductors.
Is the point that, since #12 has a full-size ground, any upsized circuit conductors require the GEC be full-size, without limitation?
bphgravity
Senior Member
- Location
- Florida
Re: Equipment Ground Size in MC Cable
This is another one of those unintended flaws when tying to apply an important requirement that doesn't work for all circumstances.
Perhaps you could provide a conductor withstand rating to your inspector based on the circuit performance using the #10 conductor. If this calculation shows that the maximum possible fault current can be effectively carried by the #10, plus or minus a few variables, perhaps they will permit the installation. I might if the contractor went through the trouble.
[ January 17, 2006, 11:15 AM: Message edited by: bphgravity ]
This is another one of those unintended flaws when tying to apply an important requirement that doesn't work for all circumstances.
Perhaps you could provide a conductor withstand rating to your inspector based on the circuit performance using the #10 conductor. If this calculation shows that the maximum possible fault current can be effectively carried by the #10, plus or minus a few variables, perhaps they will permit the installation. I might if the contractor went through the trouble.
[ January 17, 2006, 11:15 AM: Message edited by: bphgravity ]
peter d
Senior Member
- Location
- New England
Re: Equipment Ground Size in MC Cable
That code section has always left a lot to be desired, at least IMO.
Since I don't often work with oversized conductors, I am by no means an authority. But from what I have learned here, the proportion works out so that any size under #4 must have the same size EGC as the phase and grounded conductors.
That code section has always left a lot to be desired, at least IMO.
Since I don't often work with oversized conductors, I am by no means an authority. But from what I have learned here, the proportion works out so that any size under #4 must have the same size EGC as the phase and grounded conductors.
- Location
- Illinois
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- retired electrician
Re: Equipment Ground Size in MC Cable
The intent of the section covers both conduit and cable wiring methods. The rule does have its problems when the OCPD is 30A or less, but there is no easy way to write a code rule to rid the code of the problem for smaller OCPDs. The issue is not the withstand of the EGC, but rather limiting the voltage drop on the total fault circuit so that enough current will flow to quickly open the OCPD.
Don
The intent of the section covers both conduit and cable wiring methods. The rule does have its problems when the OCPD is 30A or less, but there is no easy way to write a code rule to rid the code of the problem for smaller OCPDs. The issue is not the withstand of the EGC, but rather limiting the voltage drop on the total fault circuit so that enough current will flow to quickly open the OCPD.
Don
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