Generator for 120/240V 200A service

[bendomaniac]

I need to power a panel for an adjacent business while the power company upgrades the feed from the transformer. The power consumption fluctuates but I've clamped it as high as 180A. What size generator do I need, and more importantly, I would like to learn to make these calculations for myself. Thank you for your consideration.

 

[roger]

Sizing a generator is a lot more involved than just considering the average current or wattage. For example, motor and compressor starting loads, the presence of a UPS, altitude, (yes even altitude can play a roll) fuel type, as well as other factors have to be considered. It is best to let an engineer or generator manufacturer help in this.

Roger

 

[iwire]

I do not disagree with Rogers points for permently installed generators.

But I get the impression this is just a temp deal so just oversize it.

200 amps at 240 volts equals 48,000 watts or 48 KW.

I would ask the generator rental company to send me at least a 75 KW unit.

The down side of over sizing is of course the extra rental costs and added fuel consumption.

 

[bendomaniac]

I understand motor start up draws can be up to 125% of rated amperage. The location is at sea level and there are no UPS systems. The max draw when the walk-in motor kicks with all equipment operating is just under 180A. I will only be renting the generator for a one day use. Should I still contact the MFG., or is there a base formula that I can use for this particular requirement? Thanks.

 

[augie47]

For one day, and if you want to assure the supply, I'd follow Bob's suggestion.

 

[bob]

I understand motor start up draws can be up to 125% of rated amperage. The location is at sea level and there are no UPS systems. The max draw when the walk-in motor kicks with all equipment operating is just under 180A. I will only be renting the generator for a one day use. Should I still contact the MFG., or is there a base formula that I can use for this particular requirement? Thanks.

You understand wrong. A motor can draw 6 to 8 times its normal full load amps at starting. The generator must be able to handle this short time overload. Suggest you contact MFG.

 

[iwire]

Suggest you contact MFG.

So you figure the manufacture is involved in each generator rental?

We have done a lot of generators very successfully without the manufacturer, often there would be no time to even if we wanted to.

 

[bendomaniac]

True, but were talking about a small size (10x10) walk in cooler fan/blower motor. Thanks Bob.

 

[bendomaniac]

Thanks gentleman. Ive got all the info I need.

 

[bob]

So you figure the manufacture is involved in each generator rental?

We have done a lot of generators very successfully without the manufacturer, often there would be no time to even if we wanted to.

Not only a knowledgeable electrical person, but a great photographer..
You also probably have information on the load.

OP quote " The max draw when the walk-in motor kicks with all equipment operating is just under 180A"

No information as to the size of the motor. I would not try to tell the OP how
to size the Gen with out this info. I guess he could have asked the high school kid at the rental store.