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Old 11-22-2010, 11:36 AM   #1
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Dual Pole Breaker Amperage Question

When a split-phase North American home has a dual pole master breaker with "100" printed on both of its tied switches/poles, does this mean that the house can technically draw a total of 200A from the overhead service drop? In other words, does it mean that one side of the house (served by the "A" hot/pole) can eat 100A while the other side (served by the "B" hot/pole) can simultaneously eat an additional and separate 100A — for a total of 200A being drawn at once from the utility company?

If so, then there are two more nuances to this that I'm curious about:

1) Installations are often called "100A service" or "200A service", etc. To what does this refer in split-phase North American installations? Is "100A service" a reference to the maximum amperage each of the service drop's hots can bear, or is "100A service" a reference to the maximum amperage both of the service drop's hots can bear with that 100A divided evenly between them? In other words, would "200A service" have a "200A-200A" master breaker, or a "100A-100A" master breaker?

2) Do the maximum amperage draw specifications given by 240V loads (stoves, ovens, etc.) refer to what they will draw from each hot, or what they will draw divided evenly across both hots? In other words, does a 240V 40A motor require a 40A-40A breaker, or a 20A-20A breaker?

@edit - The closest I came to finding the answer to my "100A vs. 200A service" question was this post. However, the "U" explanation offered there does not make sense to me. It sounds like the poster is insisting that a master breaker sits at the two tips of one "U" shaped circuit. But that would make your entire house 240V ... and possibly your neighbors' homes as well?!

Last edited by jcwilshire; 11-22-2010 at 11:43 AM.
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Old 11-22-2010, 11:49 AM   #2
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a two ple breaker whatever the value,20 or 100,that is per leg(one phase or side).does not double the value.2-pole 20 amp doesn't equal 40 amps.when the current reaches the trip value,breaker will trip.example:a ckt needs 40 amp 220,you need a 40 amp 2 pole breaker.leg a is drawing 30 amps,leg b draws 45 due to a grounded hot, it trips.so in other words each leg is protected at 40 amps.they are tied common so when one leg draws to much current they both disconnect.
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Old 11-22-2010, 12:45 PM   #3
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When you have a 100 amp service it means that you can draw 100 amp of 240 volt power. Since US residential power uses a center tapped transformer, you can also draw 120 volt power - 100 amps on each leg.
Power = IXE
240 X 100 = 24000 watts
120 X 100 X 2 = 24000 watts.
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