Going from PVC (concrete ductbank) to RMC (stubups/aboveground)

[SparkOmatix]

Is the following permissable:

A concrete, below-ground, ductbank system made up of PVC conduit. At every point of stub-up, a transition from PVC to RMC is performed. The RMC will have a grounding bushing on it and it will be connected to the system ground grid. Is this an acceptable installation? Note, each piece of equipment has its own ground. Any motors will also have a dedicated stringer to the system ground grid.

I extend my thanks to each and every person who contribute time and effort to this forum!

 

[dpc]

Assuming you are in the US:

RMC = Rigid Metal Conduit??

It it fine to transition to steel conduit as you propose. For grounding, all circuits should have a ground wire running with the phase conductors. As a practical matter, if you are coming up through concrete, the interface between conduit, concrete and air is a prime spot for corrosion. I'd recommend PVC-coated rigid steel conduit. We normally use a coated steel elbow to make this transition. Motors need a grounding conductor with the phase conductors in addition to any direct connection to the ground grid.



David Castor

http://www.cvoes.com

 

[SparkOmatix]

Hi David. Let me begin by saying "thank you."

Yes, by RMC I mean rigid metal conduit.
Yes, all circuits will have a ground wire.
Thanks for the recommendation regarding corrosion. It is duly noted.

 

[rcw retired EE]

Another way to combat corrosion at the concrete/air/conduit interface is wrap anti-corrosion tape around the conduit for a distance above and below the stub up point.

The tape is usually sold for protecting underground pipes.