Standby Generator Sizing 702.4 (b)(2)(a)

ramsy said:
My theory for why portable backup generators pass without load calcs, is that inspectors are more comfortable with listing requirements than code. Excluding listings for equipment having wheels in 445.6 leaves inspectors with a fragmented topic, across multiple articles, which are ignored.
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It states specifically that installations with manual transfer equipment are not required to handle the entire load, so no load Calc would be required.

I have yet to see a home owner with a portable generator with two wire start capability and an ATS.
 
You all probably know all this more than me, but the other thing people dont realize is generators consume a base of x gallons an hour of fuel no matter what the load, and if you have a ATS switch on while your at work and a 20kW generator is powering a tiny 100W 'away' load like porch light and oven clock its still going to consume a ton of fuel. Then when the family is home even a family of 4 might only have a 2000W load, lights, Fridge, Freezer, TV, phone chargers.. I suppose that's why they make them have a higher 3600 RPM than a 1800 RPM industrial 'prime mover'.
 
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tortuga said:
You all probably know all this more than me, but the other thing people dont realize is generators consume a base of x gallons an hour of fuel no matter what the load, and if you have a ATS switch on while your at work and a 20kW generator is powering a tiny 100W 'away' load like porch light and oven clock its still going to consume a ton of fuel. Then when the family is home even a family of 4 might only have a 2000W load, lights, Fridge, Freezer, TV, phone chargers.. I suppose that's why they make them have a higher 3600 RPM than a 1800 RPM industrial 'prime mover'.
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Yep. Had a couple customers surprised at their increased propane bill. One of the reasons I give them all the info on fuel consumption at the start. 👍
 
Birken Vogt said:
When I started, load calcs were not required for the permit. Then when the generator crazies hit, they were definitely required, and have been ever since. They also used to not require a gas calc, then they required gas plans in detail for the whole house, then they stopped caring after that.

Also depends which county. Some counties require the Optional Method even though it is not valid under 100 amps, which most generators are. Sssh. Don't tell them. It leads to a more manageable number anyway.
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But the calc is for the house, not for the generator. The generator is picked base on the Kva/kw result that you've got, a kw not lower than your result should be chosen per 702.4 when using hole house ats
 
Josuea1990 said:
No load shedding is being used in the videos I've watched.
What size generator would you pick for an all electric house that has a 200 A service and wants a whole house ATS without the use of load shedding? Would you pick an arbitrary number? Or would you follow 702.4 (b)(2)(a)
Thank you!
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For me it depends on the location and what the customer wants. Here in upstate NY we are never getting permits for such things. It is my opinion that a load calculation number is in fact the arbitrary number for optional standby systems.
 
electrofelon said:
For me it depends on the location and what the customer wants. Here in upstate NY we are never getting permits for such things. It is my opinion that a load calculation number is in fact the arbitrary number for optional standby systems.
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We had issues with the Generac salesman at Big Orange telling people they could run the whole house off a 12kw generator. We get there to do the install, and the customer would be mad when we would tell them it wouldn’t run a total electric house with three heat pumps!
 
hillbilly1 said:
We had issues with the Generac salesman at Big Orange telling people they could run the whole house off a 12kw generator. We get there to do the install, and the customer would be mad when we would tell them it wouldn’t run a total electric house with three heat pumps!
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Well often it does. I have installed several 12 KW for a whole house. I'm not saying every time of course, but sometimes that's plenty
 
electrofelon said:
Well often it does. I have installed several 12 KW for a whole house. I'm not saying every time of course, but sometimes that's plenty
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Do you do an ATS and load shed? I'd wager 90% of installs around my area are a portable connected to a 50 Amp inlet and a cheap manual transfer switch.
 
tortuga said:
Do you do an ATS and load shed? I'd wager 90% of installs around my area are a portable connected to a 50 Amp inlet and a cheap manual transfer switch.
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Yes, I try and talk all my customers into doing a 50 amp. Portable I tell him when an appliance goes bad switch. The gas may cost you more but it’s gonna be cheaper than getting an entire home that’s all Electric.
And if you can get all your major appliances and switch over to propane, you’re set on running your entire home off that portable
 
electrofelon said:
Well often it does. I have installed several 12 KW for a whole house. I'm not saying every time of course, but sometimes that's plenty
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I had a lady with a 11 kw, would not start her 5 ton AC. I installed a soft starter, started the AC just fine. (5 ton typically 7 kw) 10 minutes later the generator shut down for high oil temp, it was about 92 degrees that day.

Don't run cheap air cooled units against the wall like this, or anything really. Not worth it. The cost to go to the next size is just a tiny increment, and fuel consumption difference is minimal too.
 
hillbilly1 said:
But it wasn’t running three heat pumps with electric strip backup!
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Birken Vogt said:
I had a lady with a 11 kw, would not start her 5 ton AC. I installed a soft starter, started the AC just fine. (5 ton typically 7 kw) 10 minutes later the generator shut down for high oil temp, it was about 92 degrees that day.

Don't run cheap air cooled units against the wall like this, or anything really. Not worth it. The cost to go to the next size is just a tiny increment, and fuel consumption difference is minimal too.
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Yeah it all depends. Round here in the northeast I guess the loads tend to be light as many people don't have AC or electric heat. Most of my customers are ok with manual load shedding if needed. When I was an apprentice I remember we did one and the client is like "I want to be able to cook a full Thanksgiving dinner on the generator and have everything still work." So a big generator they got.
 
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