Probably should have posted this here first, but I didn’t!
Are 2, 20 amp, single pole breakers the same as 1, 20 amp, double pole breaker?
Don
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Exactly what are you trying to do?
For 240 volt circuit you (and some special multiwire circuits) you need breakers that both poles will trip at the same time.
I believe that with some brands you can use individual breakers and use a tie bar to connect the handles.
Bill,
I should have been more specific. Is the current the same between the two? Or maybe this, with a 20 amp double pole breaker, is each leg 10 amps, or is each leg 20 amps?
Don
Each pole is 20 amps
About as direct as I can expect! 8^)
Thank you.
No. There are handle ties that are made by the manufacturers and sometimes I see a field expedient handle tie made from a bit of #12. Neither of these will garantee that when one of the single pole breakers trips that the other one will be thrown.
On a 240v circuit there are two hots. During an overload both legs must trip to avoid a fire and safety hazard. The handle ties are sold for use only as a convenience for manually controlling two single pole breakers running two seperate 120v circuits not two single pole breakers misused on a 240v circuit.
For 240v circuits use a purpose built two-pole breaker. One of them is actually slightly less expensive than two single pole breakers.
Thanks 4lorn, but I never had intentions of using single throw. Just wasn't sure what 220, double throw to get. When changing a 110 motor over to 220, the amps is cut in half, but does that mean the breaker gets cut in half also. That was my question, and it was answered by Pete. Thanks.
Don
Sorry. I misunderstood what you where asking.
Generally the amperage will halve when going from 120v to 240v but use the name plate rating on the motor to size conductors. Size the breaker to protect the line. There are more complicated rules but this works well in the vast majority of the cases.
I have a friend that swears a 2 pole 20 amp for instance, is really called a 40 amp in the store. A two pole 30A, he would call a 60A. Isn't it funny how people are. I have been a electrician for 25 years and he still won't listen to me. I have even showed him breaker literature of all sorts, as well as in the code book, but there is no changing his mind.
Michael,
In another thread I think it has been asserted that if you are running two 120v circuits from different legs of the service and have them sharing a common ground, the breakers have to be yoked/tied together
I question that, but don't know for sure. Is that true?_______________________
"I may have said the same thing before... But my explanation, I am sure, will always be different." Oscar Wilde
Bob-
210-4(b) Multiwire Branch Circuits - Dwelling Units "In dwelling units, a multiwire branch circuit supplying more than one device or equipment on the same yoke shall be provided with a means to disconnect simultaneously all ungrounded conductors at the panelboard where the branch circuit originated."
A duplex receptacle by definition has two devices on one yoke, or strap, and if supplied by a multiwire BC would have to have an approved handle tie installed between the single-pole breakers, or a 2-pole breaker, so that one cannot be opened without the other. One common use is for dishwasher and disposal installations, wth a duplex rec. powering both units. The tie requirement does not apply to circuits that split apart, with no duplex receptacles having both circuits on one yoke.Be seeing you...
Tom, thanks muchly_______________________
"I may have said the same thing before... But my explanation, I am sure, will always be different." Oscar Wilde
Hi All,
I'm running a new 240v circut for a cabnet saw. I have a sub panel for the garage
that i intened to run it from. I plan on running #12 wire from a 20amp C/B. the
saw motor is 3 HP, 13 amp, 230v. Is this correct?
Thanks, Dick
Sounds about right. Double check the Full Load Amperage (FLA) on the equipment label. There may also be a note on the recommended breaker size. Always use this information as it takes precedent over any rules of thumb or the rantings of people, no matter how well intentioned, on the internet. That said I would expect no problems with the set up you propose. sounds good.
It sounds like the manufacturer rates this equipment conservatively. A good thing. Some times companies play tricks and use developed HP. A measurement that exaggerates the actual HP. They rate the motor on the energy output from full running speed to a dead stop. About like saying that a small truck will move a large load if you just use a long rope and give it a running start. You see this a lot on shop vacs and cheap equipment.
For a real comparison use the FLA. A much more standardized measurement. Please be careful. Double check grounding and work it with the circuit off. It is also safer to assemble circuits working toward the current source. Make the connections to the circuit breaker last. Use your saw in good health.
Thanks for the information.
Dick
Dick - The installation info for my Unisaw is in the manual, and specifically recommends, or instructs, to use a 20A circuit. I've heard PM66 owners say their manual says to use a 30A circuit (those motors draw a little more, ~15-17A vs my 12.4A). Both those saws have real 3 hp motors. Since the specific full-load current draw of a particular motor depends on lots of design variables, and will even vary between different motors of the same hp from the same manufacturer, it's best to simply do what the manual says, as 4LORN1 suggests and the NEC states.
Check your manual and UL sticker for information specific to your saw. Be seeing you...
I like 4Lorn1 's description. It creates an "independant trip two pole" according to the Square D digest.
You can't use bailing wire or any other method except the ul approved accessory. In the case of Square D QO breakers it is a "QO1HT". Every breaker type has its own accessory. They list at $2.40 each.
Edited 2/6/2003 4:54:24 PM ET by Booch