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I have a mwbc with two 20A breakers with their handles clipped for common trip.

Can I replace this ensemble with a single two-pole 20A breaker with just one handle?

New panel in CA.

I'm unsure whether the single handle will trip if the sum over both hot lines is 20A, versus the current setup will allow 20A on each hot line.

I suspect I can because if this were not a mwbc but 240v the breaker would tolerate 20A on each hot leg.

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  • The one caveat about using a 2-pole common trip breaker on a MWBC is you increase the chance of an undesired trip on a critical circuit. The scenario is one circuit of the pair is deliberately under loaded because it serves some critical appliances (say a freezer, aquarium, battery charger for oxygen concentrator . . .) but the other is sometimes subjected to over currents (tools, high power stereo, electric space heater. . . ). If there are two 1-pole breakers with a listed handle tie, then there is no common trip. Or you could get a 2-pole independent trip, if you can find it. – Jim Stewart Dec 13 '18 at 11:40
  • Personally (I am a confirmed skinflint) I would not change the two 1-pole breakers, assuming they have a listed handle tie. However, you must be sure that two 1-pole breakers for a MWBC are on different legs so that the neutral is not overloaded. You should be able to determine this from looking at the positions of the breakers in the panel, but I would want to use a voltmeter to see that there is 240 V between the two hots of the MWBC. Measure at any duplex receptacle of the MWBC where one hot is on one breaker and the other hot is on the other breaker. – Jim Stewart Dec 13 '18 at 12:08
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The 2-pole 20A breaker is correct for an MWBC.

The only difference between a 2-pole breaker and two 1-poles handle-tied is that the 2-pole breaker guarantees common trip, and the handle tie does not.

Yes, a 2-pole breaker will let you flow 18A on one leg and 19A on the other. The breaker has no connection to neutral and does not know or care what current is flowing on neutral.

MWBC does not require common trip, only common maintenance shutoff. Nonetheless, we recommend a 2-pole breaker, because they are available everywhere for 2x the cost of a single... rather than 2 breakers with a handle tie, because listed handle ties are often difficult to find and add unnecessary cost, and we don't want you using a nail or nothing at all indefinitely while "get a handle tie" sits on your D-list of priorities. 2-pole is also the only reliable advice when double-stuff breakers are involved.

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  • Can you insert a listed handle tie between two 1-pole breakers without removing the dead front and pulling the breakers? – Jim Stewart Dec 13 '18 at 11:50
  • I agree common trip is not required but a safer method, I have seen Handel ties not trip both in a few cases but when turned off by hand they usually work fine. Jim there are some handle ties that press on and lock onto the handles but some require the breakers to be separated it depends on the brand. I don't Cary ties any longer just replace the breakers. – Ed Beal Dec 13 '18 at 15:28
  • @JimStewart I've never seen any that could be installed without removing the breaker and deadfront. If it was possible to install a handle tie without taking the panel apart, it would also be possible to remove/defeat the handle tie without taking the panel apart. That's a big deal, Siemens sells a line of panels where breakers bolt on, like Pushmatic, they are for factories to deter tampering by unauthorized personnel – Harper Dec 13 '18 at 16:55

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