Configuring Property For Both Single Phase & 3 Phase

Thread Starter


Joined Jan 29, 2016
I'll make this as short as possible, thank you for your time.

Hotel Wired for Single Phase incoming power.

"Town Power" is Single Phase and only provides 17 hours of power.
"Generator Power" is Three Phase. Use each day while there is no "town Power."

Besides converting the generator to Single Phase, is there a utility switch of sorts that could distribute the offset?


Thread Starter


Joined Jan 29, 2016
What are the respective voltages?
What total power?
Single phase is easy to configure from 3phase.
one 240Vac line and one Neutral line coming in from town power.
That is split by two pole transformers 50 and 37.5KVa.
This ends up as 4-120Vac line, two from both transformers and a shared Neutral.

The generator power is 3 Legs of 120Vac and a Neutral.

Can the 4 - 120Vac lines from the transformers act as a 3-phase configuration into the transfer switch?
(meaning, can 1 line be taken from the 50KVa transformer and another from the 37.5 transformer to create a third 240Vac leg?)


Joined Mar 30, 2018
What you propose to do is perfectly feasible – power the hotel from the three-phase generator or the town power.

Most importantly you need an electrician who knows what he is doing to implementing the switch-over gear; also your three-phase generator needs to be adequately rated for the expected loads on each phase.

Based on the information in your posts, you have four separate 120Vac (to neutral) single phase supplies to the hotel. Given that the output of the three phase generator is 120Vac/phase (with a neutral), I would suggest each one of these three phases is fed to one of the four separate 120Vac hotel supplies. This will leave one of the four un-powered. To overcome this, two of the hotel single phases will need to be connected to a single output from the generator. If these two phases are the ones fed from the 37.5kVA transformer, then your three-phase generator will need to be rated at least to 200kVA (total).

You might be able to get away with a lower powered generator if the known loads on each phase are less than the 50kVA/37.5kVA supply transformer ratings, with appropriate overcurrent/fusing protection.

Your electrician could wire the switch over to occur automatically on loss of town power, including automatic start of the diesel generator – and revert back to town power once restored.
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