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? Thanks
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?
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.
