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Generator Cable Sizing #218792
10/15/17 02:46 PM
10/15/17 02:46 PM
brsele  Offline OP
Joined: Jul 2008
Posts: 95
Northern Ontario
How does everybody here size the cable for home standby generators? Here's the situation... A customer called me for a Generac generator. He has already installed #3 TECK cable (along with the control cable) from where the generator will sit, to the house. I believe that the OESC, CEC and NEC all agree that this cable is rated for 100 amps. If it's a continuous load, you're not supposed to exceed 80% or 80 amps. The customer wants the biggest generator he can get on this cable.
Generac says:
16kW - Max rated load of 66.6A, protected by a 70A breaker
20kW - Max rated load of 83.3A, protected by a 100A breaker
22kW - Max rated load of 91.7A, protected by a 100A breaker
Which generator would you choose?

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Re: Generator Cable Sizing [Re: brsele] #218796
10/15/17 08:26 PM
10/15/17 08:26 PM
SteveFehr  Offline
Joined: Mar 2005
Posts: 1,213
Chesapeake, VA
Unless it's a continuous rated generator (unlikely in this size/price range), it's not capable of supplying continuous service; standby rated generators are only capable of 70% average load for 200 hours/year. If it has an integrated breaker, you don't need to oversize the conductors; that breaker's probably only 80% rated anyway. He should be good up to 24kVA standby on a 100A cable. Is that 22kW really 100% rated as the Amps suggest, or is that some sort of fine-print marketing?

Last edited by SteveFehr; 10/15/17 08:31 PM.
Re: Generator Cable Sizing [Re: brsele] #218797
10/16/17 09:04 AM
10/16/17 09:04 AM
ghost307  Offline
Joined: May 2005
Posts: 934
Chicago Illinois USA
Unless the sole load on the generator is electric heat...and it's running 24/7 none of the typical residential installations are a continuous load.
I don't see a problem using the pre-installed cable at 100% of its rating.
Keep in mind that the ratings of the generators assume a completely balanced load.

Re: Generator Cable Sizing [Re: brsele] #218799
10/16/17 07:13 PM
10/16/17 07:13 PM
HotLine1  Offline

Joined: Apr 2002
Posts: 6,935
Brick, NJ USA
Going for the 22 KW unit may be the best choice depending on the $$$ differences over the 20 KW.

Based on the permits I process, 22 KW units are in the majority, followed by 20s, and 16s are few.

Common is a 200 ATS, 22 KW Gen, 100 gen, 200 utility, to the existing 200 amp panel (w/neutrals/grounds separated) and load shed for the HVACs, etc.

Re: Generator Cable Sizing [Re: brsele] #218806
10/18/17 07:39 PM
10/18/17 07:39 PM
brsele  Offline OP
Joined: Jul 2008
Posts: 95
Northern Ontario
Thanks for the responses.
22kW it is then. It really is helpful to be able to bounce things off of others.


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