I am looking at sizing a whole house generator. My question is. Would I have to include the load for an outbuilding that is used primarily as a work shop, and has a hot tub? (2008 NEC) 702.5(B)The calculations of load on the stand by source shall be made in accordance with Article 220 or by another approved method. What would another approved method be in figuring a total service calculation? The way I see it, that building and it's associated equipment are part of the total service load figure. I have a generator rep telling me that only the loads that the owner want to include have to be figured in sizing the unit and service rated switch.I have installed smaller units 8,11KW etc that utilize 10/12 circuit transfer swith panels but never had to figure for whole house scenario with service rated switch. I asked if he was referring to a load management type switch and he said no. Any help appreciated.
generator sizing
- Thread starter nizak
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Is your transfer switch automatic or manual? If auto, you need to do a full load calculation based on what that ATS could power. The only way to reduce that is with automatic load shedding equipment. If the transfer switch is manual, then the homeowner can manually load shed and you can put in whatever size generator works best for him and his budget.
With an ATS, you'd generally want a critical loads panel unless you have the budget for a 100+ amp generator (or a house with mostly gas appliances). Then, don't put things like hot tubs on that panel. Conversely, if there is just one thing to load shed, that isn't too costly either.
With an ATS, you'd generally want a critical loads panel unless you have the budget for a 100+ amp generator (or a house with mostly gas appliances). Then, don't put things like hot tubs on that panel. Conversely, if there is just one thing to load shed, that isn't too costly either.
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texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
The generator salesman is wrong given what you describe. You are correct, anything connected to the service that will be transferred automatically must be calculated per Art. 220. This can be rectified by installing auto load shedding of the non desired loads in your design to get the value needed for a given generator size.
eHunter
Senior Member
- Location
- North Texas & Georgia
What brand generator rep is giving you advice?
If the homeowner is asking you for a whole house genset and SE rated ATS, size the genset and ATS for the largest possible operating load.
Pay particular attention to the entire article 702.
ceb58
Senior Member
- Location
- Raeford, NC
The salesman will tell you any thing you want to hear to sell a unit. What size is the service? Dose the dwelling only have one panel? If there is only one panel the customer will need to decide what loads he wants backed up and, as Texie said, he will have to shed some loads or install a separate panel for the loads. Or install a manual switch and let the home owner select his own loads. Or as a final act install a generator that will handle all of the connected load.
It's an automatic switch. I could get away with using say a 100A 16 Circ ATS and a 20KW unit and selecting essential loads, but they are spread out over an existing remote workshop, a new to be constructed small home, and a 1500sq ft addition to that home 2 years down the road( a total of 3 panels)The total connected load for the circuits I would like to back up is about 70A (16 circuits). The whole house just seems like the way to go,it's the high load factor of that out building that is pushing the calc load so high. I will need to see what is available with the load shedding type switch. Thanks.
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