4 ms·

My impression is that in many European countries much lower supply ratings are normal (like 25A, I think I've even seen 17A on an apartment with A/C!) and it's

My impression is that in many European countries much lower supply ratings are normal (like 25A, I think I've even seen 17A on an apartment with A/C!) and it's just sort of accepted that you will trip the main breaker if you run too many things at once. In the US tripping the main breaker would be a pretty crazy occurrence, we seem to always spec in order to make that very difficult to do. I wonder if one difference is the safety margin applied considering the long trip time for breakers in a light overload condition... if you have say 100A service you could pull 150A for a decently long time before the main trips, perhaps for the runtime of some appliances, and over time that could lead to heat problems.

MisterTea 5y ago
> if you have say 100A service you could pull 150A for a decently long time before the main trips, perhaps for the runtime of some appliances, and over time that could lead to heat problems. Depends on the trip curve and the age of the overcurrent device. Looking at the trip curve for a Fuji BW250 (125-250 amp frame size), at 150% the device will trip in what looks like 5-30 minutes. Any load over 10x rated current is an instant trip. There was a scandal many years ago where an electrical equipment manufacturer, Federal Pacific, was caught rigging its testing machines to pass faulty or poorly performing circuit breakers. It was found that some of those breakers would carry 150%+ rated current without tripping. They were responsible for quite a few electrical fires and were sued into oblivion.