Transfer Switch Capacity...


Old 09-08-07, 07:07 AM
Thread Starter
Join Date: Sep 2007
Posts: 11
Transfer Switch Capacity...

I bought a 17.5KW generator and it came with a 60A manual transfer switch. The transfer switch is pre wired with double pole breakers of 50A, 40A, 30A . It also has 5 single pole breakers of 15A & 20A. I saw all those breakers and thought that I could wire in the two 3-ton A/C units, frig, lights etc., but then it occurred to me that even though they put all those breakers in the box, it is still only being fed by a double 60A breaker in the main box. I was planning on running only one a/c unit at a time with the generator, but 99.9% of the time the utility would have to feed both at the same time.
Do you think that the 60A breaker feed from the main can handle two 3-ton A/C units, both furnaces, frig and some light circuits on a daily basis w/o tripping? I'm wondering if it would be better to buy a interlock kit so I can pick and choose circuits...

I was going to mount the transfer box down and to the right of the main box, as the instructions that came with the setup suggest. Id say the bottom of the transfer switch box would be about 3-1/2 off the ground. Does that seem ok?

Thanks in advance, Len
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Old 09-08-07, 07:47 AM
Join Date: Sep 2002
Location: welland ontario
Posts: 5,599
17.5 KW is equivalent to 73 amps at 240 volts. I would say the 60 amp is about right for the unit you have.
Old 09-08-07, 09:34 AM
Join Date: Feb 2002
Location: port chester n y
Posts: 2,117
You tranfer the conductors of one of the two A.C. systems to the appropriate 2-pole CB in the panel-section of the Transfer equiptment. This A.C. system operates on utility-power thru the manual transfer-switch.

Switch to "generator" and this A.C. sytem is powered by the generator. If this is essentialy correct, why can't you operate only one A.C. system on generator power ?
Old 09-08-07, 11:43 AM
Join Date: Mar 2006
Location: NE Wis / Paris France{ In France for now }
Posts: 4,808
I will echo those guys comments as well but you have to understand one thing with the generator if you want both A/C running the same time what size they are ?? because the starting wattage or surge wattage that what get them pretty good there.

Is the A/C is window type or central A/C it can make the diffrence there

and also when you run on generator power dont expect the generator power to be very clean as power company supply is so if you have computer or very pricey tv put them on surge protector or UPS one of the two will help to prevent some damage to the computer [ they are pretty picky some case ]

otherwise you are pretty much set up what you need as long you follow your local code.

majory of the house useally have 10- 18 KW size that is very typically and will handle just about most load pretty easy but just watch the fuel supply if you are on propane or gasoline or diesel but natrual gas it should be not too bad most case

Merci , Marc
Old 09-09-07, 12:30 PM
Thread Starter
Join Date: Sep 2007
Posts: 11
The two units are 3ton central air. We live on the Gulf coast so it is pretty hot here during Huricane Season. I thought that during the day I could run the downstairs unit and at night the upstairs. But I didn't know if the 60A transfer switch could handle both units + lights with the utility service under everyday conditions, (ie no generator). I know the generator is large enough for what I want to do, but I'm concerned about routing all that through the 60A transfer switch.
Is it also normal to wire nut all the connections on a prewired transfer switch. The double 40 & 50A Circuit Breakers have something like #8 wire. Just wouldn't have thought that wire nuts were the way to make the connection.


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