Cost of single Phase vs 3-Phase

[mull982]

I am running a service out to a remote 120/240V panel. This panel will serve a number of circutis for which I have calculated the loads to be about 25kVA. I planned on running a 480V single phase circuit out to a 25kVA transformer and using a 480-120/240 stepdown transformer to feed the 100A panel.

My question is although I only have single phase loads out of the 120/240V panel would it be cheaper to run a 3-phase service? I realize that the cable would probably be smaller because of less current with a 3 phase service, but what about the cost of the transformer and panel equipment?

Since I do require both 120V and 240V loads, I would need a transformer with a center tapped delta connection and I would then have avaliable 120V, 208V (wild leg) and 240V. This would be a delta-delta transformer which may be more expensive.

In general for a case like this is it more or less expensive to run a 3-phase service?

 

[LarryFine]

In general for a case like this is it more or less expensive to run a 3-phase service?

The only way to know for sure is to design and price it both ways, keeping everything in mind, including POCO costs, if any.

From your description, I would lean towards keeping it single-phase. 100a is not very large, and the high leg would be useless.

 

[Jraef]

If you are talking about a new service from the utility, a 1 phase service will be less expensive. 3 phase service will come with a Power Factor meter and penalty, so you would have to deal with that in addition to the normal installed cost.

If you already have 3 phase in your facility and you are speaking of running your own service drop, then I agree that you will have to run the numbers. You will have a transformer either way, but wire is expensive now, so being able to use smaller conductors would help and the lower current would reduce your voltage drop. Then again you will have more conductors. Tough to call.