Conex with transformer

[DWooD99!]

I have a Conex shipping container with 480V 3ph incoming that feeds a 200amp Main Breaker. Then out of the main panel are three 3ph breakers that feed #1: main control panel that has a transformer that knocks down 480V to 120V for a PLC, than a second smaller 120V down to 24V for control wiring...the neutral (grounded) is tied with the ground at the secondary 120V connections. #2: A 30amp breaker to the air compressor is 480v and has a transformer inside to 120V for control wiring. the whole Conex frame is bonded to ground at the main panel. Then #3: A 100AMP breaker goes to a 10KVA transformer to knock it down from 480V to 208Y/120V, for lighting and control panel. The neutral and ground are tied at XO here.

Question I have is this:
Does the code says this is a separately derived system to be kept separate? .Because you may have the potential to have dangerous voltage differences between systems... so how do I keep the systems separate and where do I separate the neutral and ground so the secondary voltage at the 208Y/120V lighting and control panel is safely grounded?

 

[tom baker]

That is a short question with a long answer.
Are you willing to read some of the rules that apply in Art 250?

 

[tom baker]

Does your 480V feeder have an EGC (green wire) and does the conex box have a grounding electrode system, ie ground rods?

 

[DWooD99!]

The Conex is shipped to site and then feed from customers service...90% of the time the grounding conductor is run with feeders... we do not drive ground rods as the conex is bolted on a cement pad or in direct contact with earth.

 

[ActionDave]

You don't keep the separately derived systems separate, all of the equipment grounds should be interconnected by the nature of the way things get wired and bonded.

 

[DWooD99!]

so there is no need for taken the light and control panel (secondary side of the transformer) and making sure all neutrals and grounds are separated?

 

[ActionDave]

Is the secondary X0 bonded in the transformer? If it is then the equipment grounds and neutrals will be separated in the panel.

 

[ActionDave]

If you have access to the NEC handbook there are some helpful illustrations in 250.30 of transformer bonding, grounding and equipment grounding.

 

[DWooD99!]

thank you very much for the info...until next time

 

[tom baker]

The Conex is shipped to site and then feed from customers service...90% of the time the grounding conductor is run with feeders... we do not drive ground rods as the conex is bolted on a cement pad or in direct contact with earth.

But that is not an electrode that qualifies per 250.52. The secondary of the transformers require a GE connection, from where the system bonding jumper is installed, typically at the XO terminal