Step down transformer - secondary disconnecting means

[jide102]

Here's the scenario..

120/208v primary - 480v secondary. 30kva step up transformer

I would like to install the transformer next to the Main panel where it will be fed from an 80 amp circuit breaker. The transformer will feed one piece of equipment (outside of the building). Would I be required to install a fused disconnect with in sight of the transformer, or would a fused disconnect next to the equipment I am hooking up be sufficient?

Thanks.

 

[kwired]

You may not even need any overcurrent protection on the secondary if it is a three wire delta secondary and the primary overcurrent device is sized per the primary to secondary volts ratio.

The equipment you are supplying very possibly may need a disconnecting means within sight of it though.

 

[don_resqcapt19]

The transformer does not require a secondary disconnect. If the primary OCPD has a rating greater than 125% of the primary current, the secondary of the transformer itself will require overcurrent protection, but it is not required to be at the transformer. You will have to protect the secondary conductors per one of the rules in 240.21(C). The device used to protect the secondary conductors can also provide the transformer secondary protection if that protection is required.

If you ground one of the secondary conductors you will have to comply with 250.21(B). If you leave it ungrounded, you have to comply with 250.21(D).