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208V WYE to 480 volt for dust collector


May 15, 2008
Winona, MN, USA
Hi Guys,

We are installing a used Mazak 3kW fiber laser. It came from a 480V location. My plant is 208V WYE. The laser itself has an internal multi-tap transformer and it is just a mater of re-linking the transformers for 208V input.

The dust collector is 480V fixed voltage. It has a motor and PLC / HMI and various controls, but no VFD. The dust collector manufacturer says it is 480V and they don't have any interest and providing new control settings so we can adjust the various current sensors to be able to run the thing off of 208V.

So we are hooking it up with a 15kVA 208Y/120 to 480 volt DELTA transformer from eBay.

The transformer manufacturer (Eaton) notes:
"Three-phase transformers with either delta-delta or delta-wye configurations can also be reverse connected for step-up operation. When reverse feeding a delta-wye connected transformer, there are two important considerations to take into account: (1) The neutral is not connected, only the three-phase wires of the wye system are connected, and (2) the ground strap between X0 and the enclosure must be removed."

We'll feed from the 208Y/120 panel the three phases to the transformer X1, X2, X3 and a green EGC. EGC will land on chassis ground and X0 and the ground strap will be removed. Wire sizing works out to 6 AWG with a 60 amp circuit breaker for primary OCP.

The dust collector itself has a 480V three pole disconnect with 15 amp time delay fuses. This provides secondary protection of the transformer and the dust collector itself.

Given that the transformer is just serving the dust collector, it appears that unground 480 volt delta is acceptable. So H1, H2, and H3 and a green wire to chassis ground out of the transformer goes to the three pole disconnect and life is good?

Thanks in advance,