Grounding Electrode Required for Control Panel withTransformer

[richwaskowitz]

Do I understand UL 508A 16.2 correctly in that when an industrial control panel has a control transformer larger than 1000 va, that in addition to the ECG coming in with the supply conductors, a grounding electrode or electrode system will be required to be connected to the panel (for the purposes of bonding the secondary of the transformer)? Meaning that simply installing a bonding jumper from the grounded leg of the transformer secondary to the panel ground bar is not sufficient? I believe it, I am just having a difficult time explaining why this is necessary to those who are arguing that the equipment grounding conductor should be able to serve that function. If my understanding is correct, can anyone explain the reasoning behind this requirement?

 

[richwaskowitz]

I just answered my own question

I just answered my own question

After watching Mike's grounding and bonding videos, I got the answer I needed and wanted to share it with you. The reason you want (and are required to provide) a grounding electrode and its associated conductor is because that "local" grounding electrode system (even if that system is part of a larger system) will most likely be a better, shorter, lower impedance path to earth than following the equipment ground back through who knows what to get back to the supply system grounding electrode system! That's it!

 

[infinity]

Required or not IMO connecting that transformer to the building GES is a complete waste of time and money.

 

[petersonra]

It is the same rule that requires any SDS to have a grounding electrode connection. If you were to take a transformer in just add it to your electrical system in most cases you would have to ground it. This is not anything unusual. Whether it does any good or not is hard to say.

 

[tom baker]

Perhaps this is why.
Originally transformers were outside and had GE and GECs for lightning.
As power demands become higher, transformers were moved indoors and the same rules applied.
I agree connection to a GEC is of little use, and the SBJ provides the fault current path to the generator windings