Proper xfmr grounding procedure.

[electrick1117]

I'm installing a 75kva 480/208 delta-wye xfmr (it's what we had on hand) to feed a 60HP 3Ph. 208 air compressor. The compressor will be located outside the main building. There is a 480 volt 3PH 200A disconnect in the remote building fused for 110A that is fed from a 150A breaker inside which I will use for the primary. I will install a new 200A switch for the compressor main disconnect. There is an egc run with the primary conductors. Here's where the confusion comes in. Although there is a wye secondary, I do not need a neutral ran to the compressor. Do I still ground xo using the egc from the primary feed then bond to the xfmr case? Or, just leave xo open and bond the egc to the xfmr ground. To top it off, the remote building is cast concrete with only the roof being possibly connected to any of the main building metal. Should I also drive a ground rod as a supplemental ground.

 

[don_resqcapt19]

250.21(B)(1) requires the secondary to be a grounded system and you will need to run a GEC to a grounding electrode.
Don

 

[cripple]

Proper xfmr grounding procedure

Proper xfmr grounding procedure

The only requirement by the NEC to ground secondary of a 3-phase, 4-wire, wye connected xfrm is found in 250.20, which requires it to be grounded if the neutral is used as a circuit conductor and to meet is requirement the xfrm must supply premises wiring. If you are not using the neutral and does not supply premises wiring the separately derived system is not required to be grounded, you will have to install ground detectors, which will be more expensive than grounding and installing the equipment bonding jumper the 200A switch.

 

[infinity]

The only requirement by the NEC to ground secondary of a 3-phase, 4-wire, wye connected xfrm is found in 250.20, which requires it to be grounded if the neutral is used as a circuit conductor and to meet is requirement the xfrm must supply premises wiring. If you are not using the neutral and does not supply premises wiring the separately derived system is not required to be grounded, you will have to install ground detectors, which will be more expensive than grounding and installing the equipment bonding jumper the 200A switch.

How does this circumvent 250.20(B)(1)?

(I believe that this is the article that Don meant to quote.)

 

[cripple]

Proper xfmr grounding procedure

Proper xfmr grounding procedure

The code rule is written based on the xfrm supply premises wiring. The xfrm in question is supplying a single pieces of equipment. Look at the commentary in the hand book.

 

[don_resqcapt19]

Cripple,

The code rule is written based on the xfrm supply premises wiring. The xfrm in question is supplying a single pieces of equipment.

Just about everything that is installed by an electrican is premisis wiring...look at Article 100.

Premises Wiring (System). That interior and exterior wiring, including power, lighting, control, and signal circuit wiring together with all their associated hardware, fittings, and wiring devices, both permanently and temporarily installed, that extends from the service point or source of power, such as a battery, a solar photovoltaic system, or a generator, transformer, or converter windings, to the outlet(s). Such wiring does not include wiring internal to appliances, luminaires (fixtures), motors, controllers, motor control centers, and similar equipment.

Don