standby pad mounted generator

[Inverter]

Newly installed 480/277 3ph pad mounted generator at an industrial site. There will be no neutral used just a 3ph 480 motor. The generator EGC is connected to a cable tray 4/0 bare ground running in the cable tray.The neutral is not bonded to the EGC . Is a ground rod required here ?

 

[tom baker]

Is there a transfer switch?

 

[Inverter]

Is there a transfer switch?

Later down the road they will it feeds a soft start now .

 

[tom baker]

We can not answer without knowing about the transfer switch

 

[Inverter]

The transfer switch is back ordered but yes eventually there will be one 3 pole ATS no neutral this is only feeding a 3ph 480 motor. NEC says a cable tray can be used as a EGC but they’re not tied directly to the tray they used a UL listed crimp to the bare cooper ground running in the tray which should be solid . The manufacturer has written in manual a ul listed “electrode terminal “ is required and labeled “ grounding electrode Terminal “

 

[don_resqcapt19]

The transfer switch is back ordered but yes eventually there will be one 3 pole ATS no neutral this is only feeding a 3ph 480 motor. NEC says a cable tray can be used as a EGC but they’re not tied directly to the tray they used a UL listed crimp to the bare cooper ground running in the tray which should be solid . The manufacturer has written in manual a ul listed “electrode terminal “ is required and labeled “ grounding electrode Terminal “

There is no connection to any other electrical system when the generator is supplying the load, so the generator is a separately derived system and will require a grounding electrode. If the output of the generator is to be a grounded system, it will also require a system bonding jumper. If the output will be an ungrounded system, you will need a ground detector system.

 

[Inverter]

Thanks for your input appreciate it. I’m getting push back from engineering.

 

[tom baker]

Well, keep us informed on what they are pushing back on. we can easily give a code reference

 

[Inverter]

Yes if could provide a code reference that would be great.

 

[Inverter]

Not installing a ground rod

 

[tom baker]

(Sorry for the long post, its my instructor background, and others may not know this. Generators are confusing)
What is required is a grounding electrode system, which can be a ground rod or rods, or perhaps the foundation the generator could qualify as a concrete encased electrode (no ground rods required for that system)
The rules are laid out in 250.30 and its section 4. This is longish section, if you are not familiar with it take some notes as you go.
Typically the connection to the grounding electrode system is made where the system bonding jumper is installed. Although this graphic shows a TS, it is a SDS due to the neutral being transferred, Also see 250.35(A) and this is IN #1 in 250.30



This is the SDS defintion

 

[don_resqcapt19]

All separately derived systems require a grounding electrode. See 250.30(A)(4) for a grounded system or 250.30(B)(2) for an ungrounded system. Since you said that there is no connection to the neutral or any other circuit conductor of the normal power supply system, your installation meets the definition of a separately derived system.

Note that if you make it an ungrounded system, you must comply with 250.21(B) and install a ground detector.

In general the only difference between a grounded and ungrounded SDS is that the the ungrounded system will not have a system bonding jumper. The other bonding and grounding requirements are the same.