Billy Shaffer

Billy, I know a guy who has been advised to buy a 50 KW 3 phase generator for back up to his store, 6 chiller boxes, 3 X 5 ton A/C units and the normal lights, etc. He has found a 60KW single phase, why would that not work, why would he need a 3 phase to only wind up stepping it down.

Thanks

If your friend has no need for 3-phase, then the 60Kw unit would work just fine.

He should check with his refrigeration guy and ask if his equipment is 3 phase or not. If it is and he gets a single phase genset then why bother it won't run his most critical equipment.

If he has three phase service to his business, and actually uses more than one phase, he needs a three phase generator. Whether or not his equipment is three phase is besides the point.

Assuming he has three phase service, uses all three phases but has no three phase equipment, he COULD use three single phase generators. But who would want to do that?

That is a point that I should have mentioned, his equipment is single phase but the fixed power coming into the building from the road is 3 phase stepped down by transformer. He is thinking they are recommending 3 phase generator due to the wiring of the building, this is not in the US, but it's 60 hz.

It is 3 phase into his business from the power provider, it's a new build with a grocery on the first level and a bar/restaurant on the second level, 45 X 90, he is not sure what it will take to cool it, the electrical contractor told him he needs 40 tons of AC which even in a hot climate sounds like a lot.

LAA first off if ALL ?? his equipment is ONLY single phase (you sure), sure he can use a single phase Generator WELL DUH
Often times larger AC units are either three phase (preferred and more efficient) or at the minimum 240 volt single phase BUT IM TAKING YOU AT YOUR WORD HIS IS ALL SINGLE PHASE ????????

Is the generator you mentioned a 120/240 Volt Single Phase Three Wire (I would assume) ????????????????


That being said, subject to how a three phase generator is configured (like say its 208Y 120 Volt Three Phase Four Wire) such could provide him with three legs of 120 VAV Line to Neutral which is a good balance and efficient generator use. Also some (not all) three phase units can run on EITHER 208 or 240 and my example ONLY has 208 three phase.

You ask "why would he need a 3 phase to only wind up stepping it down"

Its not necessarily so its "stepped" down, as noted above perhaps a three phase service is providing THREE LEGS OF
120, that's NOT stepping it down its ONLY providing three legs of 120 VAC Line to Neutral if the service is 208Y 120
Volt Three Phase Four Wire

Sooooooooooo if ALL he requires in single phase, THE GENNY YOU MENTIONED WILL WORK. If he needs three phase it WILL NOT WORK.

I need to know more to better answer the question

John T long retired electrical power distribution design engineer

Three phase service panel has three buss bars as opposed to two in a single phase panel. If he only has a single phase generator, only 2/3 of his circuits will work.

PS You say below "He is thinking they are recommending 3 phase generator due to the wiring of the building"

THAT MAY WELL BE TRUE

If the buildings electrical distribution and panelboards are all configured for Three Phase Four Wire

THEN YES IF HE IS SIMPLY POWERING THE ENTIRE BUILDING BY A GENERATOR USED TO REPLACE THE UTILITY THEN YES HE NEEDS A THREE PHASE GENERATOR WITH THE SAME CONFIGURATION AS THE UTILITY IS PROVIDING. That may be 208 Y 120 Volt Three Phase Four Wire orrrrrrrrrrrrrr it may be 120/240 Volt Three Phase Four Wire Center Tapped Red Led DELTA

BOTTOM LINE the utility provider likely knows what he needs and it may be wise to rely on them VERSUS anything said here (me included) because we don't know his distribution system. If its all set up for three phase distribution (even if all loads are single phase) and he simply want to plug instead to a generator THE HE NEEDS A THREE PAHSE IDIENTIAL CONFIGURED GENERATOR

Your question is more complex then can be answered here by ANYONE until we know his exact configuration SO DONT BET THE FARM ON ANY ANSWERS HERE

John T Retired Electrical Power Distribution Design Engineer

EXCELLENT POINT and to take it even further we don't know if his utility is providing DELTA or Y Service???

SURE a single phase generator will work to power single phase loads BUTTTTTTTTTT is he using it as an emergency backup and feeding his distribution system or what?? And if so then NOT ONLY does the genset needs to be the same voltage and phase BUT ALSO the same configuration, Y or Delta etc.

Id bet the farm moreso on what the utility provider says then any of us who aren't there !!!!!!!!!!!!!

John T Retired Electrical Power Distribution Design Engineer

If he has three phase feeding the building. Then yes he will need a three phase generator. Most codes that I know require it.He should also consult an electrical company. See what the power system is like and what load is on it. I have seen single phase backing up three phase. But it creates a mess. Two dead circuits and one live one. So people add to the live one. Pretty soon you end up with an over loaded circuit.

The main thing is. Make sure every thing is up to code. It will save you from problems in the long run. I have seen many lose everything by trying to beat the code. Are you sure that generator is single phase only. Most in that size could be wired for 3 phase. Unless it was a special order. Can you get me the model and serial number from it

If it is outside the US. Then he really needs to check with the locals. There are some strange systems out there. As JT posted. Need to know what system it is.

I worked on a project a couple years ago where the electrition was confused about 208/240 and had some difficulty getting it straightened out. He did burn up all the fan motors in the big coolers.

I agree with the others, too much unknown.

The 3 phase could be wye or delta, local codes need to be applied.

I would do what the local authorities recommend.

He has not bought it yet, there is also a 3 phase for sale that he can get reasonable, with all the confusion I told him he better wait and make sure of what he has, this building is not in the USA and he did not trust the local electrical contractor. The guy I know is the builder, apparently the electrical guy already had him buy a bunch of stuff that is not right or now is not required. My Son has a container load of small contractors equipmemt bought up for his company and the generator is the last piece needed before ready to ship it out, the builder needs the equipment and wanted to rush the generator purchase, I advised against buying until he was sure of what he needed and I think he has decided to get someone else to come check it out first. I dont think the power company people are much help where he's at and I dont think there are inspectors that come out, must not be a code enforced either.

Exactly, some motors will work on 208 OR 240, others not so well. 208 is a Y system while 240 may be a Delta. Also if its a Red Leg Delta, one of the 3 lines is 208 to Neutral versus 120 YIKES

John T

"I advised against buying until he was sure of what he needed and I think he has decided to get someone else to come check it out first."

EXCELLENT ADVICE better then any here BECASUE WE DONT KNOW HIS DISTRIBUTION SYSTEM. Is it 208 Y 120 Volt Three Phase Four Wire orrrrrrrrrrrrrrr is it 120/240 Delta????????????????????????

Sure single phase units will work an a single phase genset BUTTTTTTTTTTT his distribution may be three phase and if he wants to use it then he needs a Three Phase Genset OF THE SAME VOLTAGE AND CONFIGURATION, Y OR DELTA

Hope this helps

John T

You gave him very good advice. Find out what he really needs before he buys anything. I have been on many jobs where they thought they needed this but needed that.Spent the day at a sewage plant converting the system from 480 to 240. Did a start up on a 100 bed nursing home. Back up was a 3412 Cat with a twenty thousand gallon fuel tank. We had to add two houses to keep it from wet stacking. Just make sure you need it,before you buy it.