Upsizing ground for voltage drop

[aaronroy]

I recently ran a 120/208V,1Ph power feed to a panelboard across a parking lot. The distance of the run caused me to have to upsize the phase conductors from #4 to #4/0. Unfortunately I forgot to upsize the ground conductor proportionately to the upsizing of the phase conductors as indicated in NEC 250.122. This would have changed my #8 ground conductor to a #1 ground conductor.

My question is can I expect to have grounding issues due to the undersized ground, and if so can the ground wire be supplemented with a ground rod at the location of the panelboard?

 

[don_resqcapt19]

Re: Upsizing ground for voltage drop

My question is can I expect to have grounding issues due to the undersized ground, and if so can the ground wire be supplemented with a ground rod at the location of the panelboard?

It will take the OCPD longer to trip when there is a fault. This is because of the current limiting that results from the impedance of the EGC. The addition of ground rods will not help.
Don

 

[bphgravity]

Re: Upsizing ground for voltage drop

This is a prime example of how the code's terminology only helps to confuse people about what purpose each component of circuit is for.

The EGC proivdes the effective fault path for current to flow. The less impedance this circuit has, the faster the overcurrent device will operate as stated by Don. Earth nor its connection to the electrical system plays any type of role in this operation.

The danger with you installation is that you have significantly decreased the impedance of the ungrounded circuit which increases the available fault current of the system during a ground fault. The #8 may not have the withstand rating for this type of event.

So in my opinion, you have no choice but to re-pull the proper sized EGC to ensure you have met the minimum requirement of the code. And get out of your head that the real "grounding", that is, the connection to Earth has nothing to do with equipment bonding.

 

[peter d]

Re: Upsizing ground for voltage drop

Why doesn't the NEC provide some clear guidelines for doing this?


I have noticed this is not a well understood concept in the field, and many violations is the result.

 

[infinity]

Re: Upsizing ground for voltage drop

What kind of conduit did you use?

 

[aaronroy]

Re: Upsizing ground for voltage drop

Infinity - Unfortunately it was PVC piping.

Thanks for the help guys!

 

[benaround]

Re: Upsizing ground for voltage drop

Would this not be considered a seperate structure (the panelboard) and require a GES to the EGC terminal bar?

Of coarse,this is in addition to the increase in size of the EGC.