Transfer switch grounding/bonding

[BoMaFl]

Existing setup is 120/208, 4 500mcm conductors in 3" pvc from meter ~100ft to mdp. Meter is grounded to building steel. Mdp has ground rod. We are looking to install a transfer switch next to the meter and run the service through the transfer switch.

Since the transfer switch will become the first means of disconnect, the ground and neutral will be bonded there, and the mdp will need to have grounds/neutrals unbonded.

1. For the transfer switch, will a ground rod be needed, or can building steel be used?

2. For the mdp, can the existing ground rod be used, or will a new grounding conductor need to be ran from the transfer switch? If so, can it be ran outside the pvc?

 

[don_resqcapt19]

If the steel is a qualified grounding electrode that will be fine.
You need an EGC from the transfer switch to the MDP It needs to be in the raceway with the circuit conductors unless you can get the AHJ to let you use 300.3(B)(3).

 

[Elect117]

1. For the transfer switch, will a ground rod be needed, or can building steel be used?

All existing electrodes should be re-used.

NEC 250.50 is the code section for this question.

Technically, the way 250.50 is worded, you should also reconnect the rod type electrode as well.