Regarding this breaker specifically (Square D model QO220CP): This is a double pole 220V breaker, but with only a single switch. Does this behave identically to a pair of single pole breakers connected with a tie bar? i.e. assuming the load gets unbalanced and pulls 20A through one leg and 0A through the other (all returning on the neutral), will it trip? They don't have the schematic or this level of detail posted so it's difficult to tell.

 

This is a double pole 220V breaker, but with only a single switch. Does this behave identically to a pair of single pole breakers connected with a tie bar?

Yes.

A double pole breaker (with either 1 switch or 2), or 2 single pole breakers tied together, or two single pole breakers next to each other will connect to both bus bars:

 

I am guessing that by " but with only a single switch" you mean only a single operating lever. So either line can trip both sides. THat is standard and in fact I would trust it more than those that have two levers tied to each other. It should function just as well for loads without any connection to neutral.

 

Seeing as how ANY 20 amp breaker should have a minimum of 12 gauge wire, if either leg exceeded the trip point both lines (L1 & L2) should de-energize. To assume you could see 40 amps on one leg and zero amps on the other would mean exceeding the rating of a 12 gauge wire. So they must both trip even though there's only a single lever.

I've taken dual breakers with the tie bar and cut and removed the tie bar to achieve two independently operated breakers with no ill effects. Each (now) individual breaker behaves as an individual breaker. Tripping one does not affect the other.

I am guessing that by "with only a single switch" you mean only a single operating lever.

There's no need to guess if you clicked the TS link.

 

Breaker in question:

This seems more reasonable:

 

Thanks all for the replies. The use case is, this is the breaker between my backup generator and my house. Just like the utility connection, my generator gives me two 110V legs out of phase, so I can run both 220V loads and 110V loads in the house. This creates the possibility that one side could see the full 20A while the other side sees 0A, depending on what is turned on inside the house, so I just want to be double sure that an over-current on either leg would trip the breaker. Re-reading the title, I see that it says "120/240V" and not "240V", so this must indicate that an overcurrent on either 120V leg must cause it to trip, else it would be advertised as 240V only.

 

Seeing as how ANY 20 amp breaker should have a minimum of 12 gauge wire, if either leg exceeded the trip point both lines (L1 & L2) should de-energize. To assume you could see 40 amps on one leg and zero amps on the other would mean exceeding the rating of a 12 gauge wire. So they must both trip even though there's only a single lever.

I've taken dual breakers with the tie bar and cut and removed the tie bar to achieve two independently operated breakers with no ill effects. Each (now) individual breaker behaves as an individual breaker. Tripping one does not affect the other.

There's no need to guess if you clicked the TS link.

NO!! the 20 amps is for each, not just the total .