Math Behind 83% Rule for Residential Feeder

nizak said:
How overloaded can a POCO xfmr be and still work effectively? I mean still producing a voltage that is within their specs.
4x
5x
?
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It is not really overloaded...it just shows how the load calculations in Article 220 result in service sizes much larger than the actual real world loads. The utilities size their transformers based on the actual real world loading that the see on their system.
 
Carultch said:
You'd have to go out of your way to deliberately turn on more loads than even the most careless user would turn on at the same time, to load your service to 90% its rating. I could also see it happening, from renovating an existing service to replace gas appliances with electric appliances. Since a lot of Watt-intensive loads are time-flexible, you can plan around this issue with whole service metering that pauses these loads any time there are high load conditions of other loads.
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In my case I only started down the rabbit hole because its a hunting cabin that sits with the main off most of the time. So it starts cold cold when we show up and then the 50 amps of electric heat run for 16+ hours flat out. The fridge also starts up, as does the electric water heater and well pump so basically everything but the TV and microwave are continuous loads. There's also no "fluff" loads aside from the general lighting load and 2 circuits. No laundry either.

With that said its a hell of an edge case. The water heater could be left off for a while obviously you dont want to depend on user intervention.
 
tp_spark said:
I only started down the rabbit hole because its a hunting cabin that sits with the main off most of the time. So it starts cold cold when we show up and then the 50 amps of electric heat run for 16+ hours flat out
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So if there some initial voltage drop at start up the resistive loads will just take longer to heat up.
 
nizak said:
Which leads one to believe how little 320/400 amp residential services are really required.

Yes, the load calc tells us we need to install it but the real data tells a different story.

I have never in close to 30 years experienced a tripped 200 amp main breaker because of an overload.
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It's all part of what I call Big House Disease. Whatever is adequate eventually gets up sized and becomes the new standard. Then an architect or engineer or contractor wants to add a little wow factor to their design so they go one step bigger and that becomes standard. Now to get the wow factor things have to be sized even bigger, and so it goes. It's not relegated to only electrical, you see framing and foundations ten times bigger than it was in the 80s.
 
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