Great, I'm glad for this new information. So when I go out to look at my breaker box which is billed as 200A (or 400 which they will at least tell me is really 320) service and it has two 100A (or 200A) breakers for a house/garage full of loads, I just hope it doesn't burn down?
As a home owner how will I ever discover this in a non-catastrophic way? Will I put an ammeter clamp on at the breaker box with an alarm on it? Will I know the load of everything that is plugged into that service? The breaker won't blow, but the building will burn down... and it's not the fault of the electrician who installed it and code enforcement says it's fine?
As examples of non-continuous loads that are likely to be continuous for 8 hours or more: a double oven during Thanksgiving, halogen flood lamps at night, or an electric space heater during winter. Oops, you burned your house down for Christmas.
(edit) Discussing this with an electrician, he says that in fact the breaker will flip after extended/continuous load near the breaker limit. It would not be considered a hazard, because the home owner would experience the breaker flip each time before there was a problem. He also said that it's the difference between running at 75 vs 100% of rated current is about 15C of increased temp on the wires and also not a concern for copper.
Yeah, your breaker box that's billed as 200A and has a 200A main breaker and wiring rated at 200A is quite safe. The breaker is designed to trip after a certain amount of time depending on RMS current, and the wiring is supposed to be able to tolerate that with some safety margin.
Your 40A (or whatever) oven isn't a 40A continuous load even on Thanksgiving. It'll draw 40A (maybe) while heating up, but it'll use much less while maintaining temperature.
If you really want, you can probably melt your breaker box, though. You'll need some really nasty nonlinear loads. Off the top of my head, with standard single-phase service, you want lots of even harmonics so that you draw 200A from each phase but put more like 400A on the neutral. Since your breaker doesn't sense neutral current, you won't trip it. (I suspect you'll acutally fry your utility's transformer long before you melt your breaker box, though -- most utilities use a rather different formula for transformer sizing and can't actually supply your rated current for very long.)
As a home owner how will I ever discover this in a non-catastrophic way? Will I put an ammeter clamp on at the breaker box with an alarm on it? Will I know the load of everything that is plugged into that service? The breaker won't blow, but the building will burn down... and it's not the fault of the electrician who installed it and code enforcement says it's fine?
As examples of non-continuous loads that are likely to be continuous for 8 hours or more: a double oven during Thanksgiving, halogen flood lamps at night, or an electric space heater during winter. Oops, you burned your house down for Christmas.
(edit) Discussing this with an electrician, he says that in fact the breaker will flip after extended/continuous load near the breaker limit. It would not be considered a hazard, because the home owner would experience the breaker flip each time before there was a problem. He also said that it's the difference between running at 75 vs 100% of rated current is about 15C of increased temp on the wires and also not a concern for copper.