2 ms·

Since our voltage is 120/240 volt split phase or 120/208 open Y service (less common) we tend to need higher currents for main breakers/fuses. The old standard

Since our voltage is 120/240 volt split phase or 120/208 open Y service (less common) we tend to need higher currents for main breakers/fuses. The old standard for a home was 100 amps whereas modern homes are built with 200 amp mains. I suppose the low cost of air conditioning and heat pumps has raised this demand. Otherwise our lighting and appliance loads have become more efficient. A 230/400V open Y service at 25 amps is just 10kW which to me sounds like an old standard or mains for a small 1-2br apartment. I'd expect at least a 50-60A service. Though I know some (many?) homes in EU are on actual 3 phase so 25A at 400V 3 phase becomes 17.3kW which is not far from the 24kW a 100A 120/240 service provides. Still anemic but quite a bit of power for a 1-4 person household living modestly. Though in the USA it seems utilities make residential 3 phase difficult or impossible to obtain as you might do commercial stuff with that electric without paying commercial rates or your neighborhood is served by a single phase feeder.

jcrawfordor 5y ago
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.

jcrawfordor 5y ago

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.