generator requirements

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Roach

Member
Hi guys , I have a question please .
I have a friend who needs to create a generator situation for when there is a power outage.
It is for 3 different circuits , 2 of which are 30Amp 2-pole circuits for 2 seperate refrigerator units in a restuarant, the third circuit is for lights which is 20 amp single pole.
My question is this He wants to supply the panel from a generator panel that will be fed from a protable gas powered generator.
I need to know what size generator will be needed to accomplish this?
Can someone please tell me how to calculate this properly.

Thanks
 

360Youth

Senior Member
Location
Newport, NC
Check your data plate info for running amps and start up(LRA), if any, and add in your lighting load. Factor in any continuous duty percentages that may apply, and buy a big enough portable.
 

spikes2020

Member
Location
Nashville, TN
I just estimated each frig has a 3hp compressor motor based on the 30A breaker. It could be a little bigger or smaller. Additional 1.3kW worth of lights maybe~


Final Running Load: 9.6 kVA
Electric Supply: 60Hz 240/120V

I would get around a 10 to 15kVA~
 
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Roach

Member
Ok thanks for your quick response. If you would'nt mind can you tell me how to do this calculation using the examples I gave?
 

boxs21

Member
have you check to electric company? for your matter
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Roach

Member
Yes he did speak to the local authorities and this is the reason he is required to use a portable gas powered generator. For some reason they won't allow a guardian stationary generator.
But my question is really how to calculate the size generator needed, for instance the response above from Spike I believe gives me the answer, now I was wondering if maybe Spike or someone else might tell me exactly how to do this calculation.
Obviously we will not be doing this job ourselves , I really was just hoping to be well advised and have the knowledge of the calculation in hand .
 
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spikes2020

Member
Location
Nashville, TN
Ok thanks for your quick response. If you would'nt mind can you tell me how to do this calculation using the examples I gave?

With the limited information i did a quick study, normally i am sizing gen-sets that are in the 100's of kW but anyway~

Well have generator sizing software made it easy. I had to estimate the size of the motors, I did the maximum size they could be off that breaker (by the code). I assumed that Motor 1 would be on pase 1-2 and motor 2 would be on phase 2-3. I also knowing what little about AC units assumed they were capacitor started.

Lights are not a big thing so i wouldn't worry about them unless we are lighting up a hotel.




LoadReport_Page_1.jpg

TransientReport.jpg
 

Roach

Member
Wow , thanks Spike. It seems you are well versed on this stuff. I was actually hoping there was a mathematical equation I would use to determine the generator size . Having a generator panel with 2-30amp (2 pole breakers ) and 1 single pole 20 amp breaker. I was hoping there was a way to solve this equation without software.
I don't mean to sound ungrateful but is there a way to do this on paper?
 

spikes2020

Member
Location
Nashville, TN
No problem, with such limited information all we can do is guess, and in estimating i do a lot of guessing and assuming. If you had more information on the motors and lights it would make it possible to do something on paper. But most of that would be looking at the starting curves of those motors.

Sorry to put it this way but "bad information in, bad information out" You get out what you put into it, so if you want the fine details they have to be there from the start.

Some details that would be needed:

What type of starter are on those motors?
The name plate of the motors?
Size of and number of lights, along with their type?
Amount of cable running to each load?
What is the altitude of the generator and climate it is sitting in? (ever try and start your car on a cold day? now try it in drive and trying to accelerate)

(all of these could play major roles in the size of the generator on paper)

Things to make the generator smaller:
could those motors be staggered so both would not run at the same time?
could you use a soft starter on the motor?
 
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kohler power

New member
stand alone generator

stand alone generator

How far can a stand alone generator be from a window or door? I can't find that in the code book. :?
 
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