480v or 120v

[AE-29]

I have to install power for a load panel to feed a 240v/43amp rated load and 2, 120v service outlets. The service options are 480v/277v (3) phase no neutral or 208v/120v. The run is 350ft. If I use the 480 option I'll need to step down the voltage. My question here is what would be my neutral concern for the 120v loads. Now if I use the 208 option I would boost the voltage after the ckt bkr for the 240v load. My question to this is the transformer rating needed either options.

 

[wireguru]

sounds like running 480 and using a 480-120/240 single phase transformer would be the best way to go. Without knowing the load on the two 120v circuits and considering them to be two x 20a, I come up with something around a 15kva transformer.

 

[augie47]

Single phase 240v load = what wireguru says... if your 240v load is 3 phase, then, they do make a 240 transformer 3 phase with a 120 tap, but they are normally limited to 5% of the kva rating on the 120v load. A possibility, but you would need to verify your 120v load.

 

[wireguru]

Single phase 240v load = what wireguru says... if your 240v load is 3 phase, then, they do make a 240 transformer 3 phase with a 120 tap, but they are normally limited to 5% of the kva rating on the 120v load. A possibility, but you would need to verify your 120v load.

good catch, I have this bad habit of automatically thinking single phase when I hear 240. In this situation, if I needed 240 3ph, and 120, I think I would install two smaller transformers.

 

[LarryFine]

... 480v/277v (3) phase no neutral ...

No such animal.

 

[AE-29]

good catch, I have this bad habit of automatically thinking single phase when I hear 240. In this situation, if I needed 240 3ph, and 120, I think I would install two smaller transformers.

the loads are all single phase. I also came up with a kva rating of about 11kva. There is a desire to keep the cost as low and thats part of my leaning to the 208v option and boosting this voltage to about 236-240. 15kva transformer compared to a buck=boost has about 1500-2000 dollar difference. I know that these transformers can often handle excess of what they are rated.

 

[augie47]

The other criteria will be voltage drop. Roughly you are looking at the difference between a #1 for 50 amps at 208, or a #6 for 25 amps at 480 (for 3%---#4 vs #10 for 5%).
Since you would need to purchases transformers in either event, my guess would be that the total cost..feeder + transformer would end up less expensive with the 15 kva 480/240-120 but I didn't actually run any numbers.

 

[wireguru]

15kva transformer compared to a buck=boost has about 1500-2000 dollar difference.

I think maybe you need to beat up your supply house for some better pricing on transformers, or get quotes from some places that just deal in transformers. You should be able to get your hands on a 15kva 1ph 240/480x120/240 (AL winding) for under $1,000.