hypothetical circuit breaker question

Old 02-12-04, 02:19 AM
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hypothetical circuit breaker question

lets say i'm installing an electric dryer and i've got my 10 awg running to its own breaker on the panel. i need to use a 30A 240V rated breaker. normally i would recommend a "thick" double pole breaker that uses two slots(ie two 110V sources) on the panel. but the "thin" double pole 30 (that uses one slot) is also rated at 120/240V. So can this also be used?

Is it saying it can be used in a 220V circuit or that it supplies 220V to the circuit? And if it IS supplying the 220V how is this so when in the panel it is connected to only one power bus?
(as i write this i think i am answering my question...2 hot lines are going to connect to the same power bus... is that not right?.....And the "thick" is just used for the convenience of not having to pigtail the hot connections)

Another question: Let's say we want to use the "thin" to supply two separate 30A circuits....we once again have to connect two 110V lines to the beaker's power bus right?

I guess what has got me confused is that when hooked up for a dryer the two poles are acting like in series supplying a total of 30A but behaving in parallel with 30A on each pole while connected to two separate circuits.

thx in advance......just clearing up some specifics..

p.s. let me know if i need to make anything clearer for a proper answer...
Old 02-12-04, 05:43 AM
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The power supplied to your home is supplied as two legs, each 110 volts measured to the neutral, which is grounded. You can power a 220 volt appliance with this by using each leg, with one hot wire connected to each leg.

This is why circuit breaker panels alternate legs to each full size breaker slot, so you can install a double width breaker and get 220 volt power.

using a tandem breaker will not getr you 200 volts, but will get you two 110 feeds that match each other. Measuring across these wires will yield zero volts.
Old 02-12-04, 07:35 AM
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For most panels, a tandem breaker cannot provide 240 volts. But for some panels (e.g., GE), such a breaker can provide 240 volts, but only if inserted in the correct position. So the answer is "maybe, but probably not". What brand and model is your panel?
Old 02-12-04, 11:58 AM
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Does the breaker connect to both bus bars or only one, if it is a thin that connects to just one it is giving you 2 30amp circuits that when conected will still only give you 110 volts
If it connects to both bus bars it should give you the 220

Usually the ones that connect to both bus bars have 2 single 15amp breakers on the side making them still double wide but getting 2 15amp circuits and 1 2pole 30amp service. The 2 swiches for the 30amp circuit and usually bound together some how.
Old 02-12-04, 11:49 PM
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So the answer is "maybe, but probably not". What brand and model is your panel?
Well this was actually only a Hypothetical question/situation. But were it to be real it'd most likely involve some Cutler-Hammers or Square-D (QO or Homeline); doesn't matter in this case though.

But yes I got my questions answered. Somerimes the specifics can be the trickiest...you just have to spell it all out.

Thank yall for the help.

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