Two Voltages - What size grounding wire?

[Dale Hayes]

Inside a control panel there is a 480v, 500Amp, 3-phase circuit breaker with several contactors attached to a heater load. There is also a 120V, 1-phase control circuit supplied from a 480V to 120V, 500VA 1-phase control transformer.

For grounding purposes there is a #2 GA grounding lug at the panel grounding bar - sized for the 500Amp circuit breaker .

The panel enlosure itself is supplied with (3) grounding stud connection points for (2) grounding wires.

One grounding wire is attached from a stud on the inner wall of the enclosure to the enclosure door and (1) wire is attached from the same stud at the inner wall of the enclosure to the removeable inner panel.

For the (2) grounding wires that connect the enclosure to the door and to the inner panel - what wire size is needed?

Are these (2) "enclosure/door/panel" grounding wires sized for the 500Amp circuit breaker or for the 120V 500VA 1-phase control transformer?

 

[Dale Hayes]

I probably shoud have worded this as Two Voltages, Two amperages - What size grounding wire?

 

[Volta]

It is nice to have doors and inner panels bonded. Isn't always required, but consider what is likely to energize those surfaces. You should know the OC rating of the circuit feeding the panel. If fed from 600 amp, for instance, you might want a #1.

 

[vinster888]

i would say its based on the largest ungrounded conductor

 

[Pierre C Belarge]

Grounding electrode conductors are sized based on the size of the ungrounded service conductors. Table 250.66

Equipment grounding conductors are sized based on the overcurrent protective device protecting the conductors. Table 250.122