EGC feeder question for MCCs

[lightlytoasted6]

Hello,

My journeyman and I are currently installing a new motor control center for a customer, when we encountered a problem. We were contracted to install 1.5" RMC to run the conductors between the disconnect switch (on a mezzanine downstairs) and the unit. Unfortunately, no one bothered to check FLA for the machine being installed, and, where we were originally going to install 1/0 conductors, we now need to pull 2/0 conductors in. To add, the pipe is already installed, so we are looking for alternatives where the EGC is concerned, to avoid having to demo and reinstall larger pipe. According to 250.118, the conduit itself is acceptable as an equipment grounding conductor, but would this be kosher for feeders? I have yet to find anything to the contrary in the code. Could we simply attach a ground bushing and run a #6 jumper in each respective end? Thank you for your time.

 

[lightlytoasted6]

I guess I should clarify, as well as some results I found on my own:
- 480 volt feeders
- 215.6 refers me to 250.134. If it doesn't involve separate buildings or structures, ranges or dryers, or using a neutral as a grounding conductor, it kicks me back to 250.118. So, my question at this point: Would there be any difference, if you used the pipe as an EGC, bonding it to ground bus at the MCC and disconnect, as opposed to doing the same thing with a conductor in the pipe itself?

 

[don_resqcapt19]

What type of conductors are you using? Have you done a wire fill calculation to be sure you can't install the three 2/0s and the EGC in the conduit?
The code permits the conduit to be the EGC and assuming clean punched holes in a metallic enclosure, you don't need anything more than the standard locknuts.

 

[lightlytoasted6]

What type of conductors are you using? Have you done a wire fill calculation to be sure you can't install the three 2/0s and the EGC in the conduit?
The code permits the conduit to be the EGC and assuming clean punched holes in a metallic enclosure, you don't need anything more than the standard locknuts.

We are using THHN. Looking at the conductor fill calculation, it appears we should have enough room to fit our #6 EGC. Thank you for your input!

 

[lightlytoasted6]

Well.

Well.

:rant:

Guess we needed 3/0, not 2/0. Our 1.5 RMC would be overfilled by .0254 sq. inches. In the interest of time and money, we could use the pipe as our EGC. My JW prefers a conductor as opposed to a pipe, as over time, the couplings on those pipes could come loose, and compromise the function of the ground in the event of a fault. But, if that's the route we have to take, it still appears to be code legal.

 

[don_resqcapt19]

You could check the wire fill calcs for compact strand conductors.

 

[jumper]

:rant:

Guess we needed 3/0, not 2/0. Our 1.5 RMC would be overfilled by .0254 sq. inches. In the interest of time and money, we could use the pipe as our EGC. My JW prefers a conductor as opposed to a pipe, as over time, the couplings on those pipes could come loose, and compromise the function of the ground in the event of a fault. But, if that's the route we have to take, it still appears to be code legal.

Your JW is worried that RMC couplings are gonna come loose? EMT maybe, but not RMC if installed correctly IMO.

 

[kwired]

Your JW is worried that RMC couplings are gonna come loose? EMT maybe, but not RMC if installed correctly IMO.

Same here - if talking about threaded raceway and couplings, what is going to make them come loose if they were tight to start with? If using compression or set screw fittings that is more understandable.