Transformer Wiring Application

[ROHM]

I have a 480V MCC Bucket that is configured with three phases. I would like to use it to power a single phase 15 KVA 480 to 240/120V transformer. Can I just run a 3 conductor cable with ground and only use 2 of the three conductors and tape the other one up?

Has anyone done this before?

What would be some feasible options?

​

 

[infinity]

Can I just run a 3 conductor cable with ground and only use 2 of the three conductors and tape the other one up?

Sure. Just because the cable has more conductors than you need doesn’t mean that you can't use it.

 

[don_resqcapt19]

Many MCC buckets use motor circuit protectors and not thermal magnetic breakers, so if the bucket has motor circuit protector, it can't be used to supply other loads. It can only supply motor loads when it is part of a listed combination starter.

 

[ROHM]

I have a fused disconnect bucket. I plan to just have a 2 1/C wire connected to two of the three phases. It would be similar to tapping off an existing three phase service that has a a disconnect.

The other question I have is that if I have a 15 KVA 480 service with three phase, that has a load of 18A and a distance of 555 feet, a conductor size of 8 AWG 3/C.

With a 480 service single phase, that has a load of 31.25 A which gives me at a distance of 555 feet, a conductor size of 4 AWG 2/C.

Is that calculation right? I would think you have a bigger wire since you have less wires for a single phase service.

 

[augie47]

If you are trying to maintain a 3%VD, i get the same numbers #8 for 3phase, #4 for single phase due to the current increase

 

[jim dungar]

Don't forget your primary side conductors must be protected by the primary protective device. Most installations use at least 125% to allow for energizing currents.