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I had a quad breaker that went bad. It had 30A outer pair for the dryer and 20A inner pair for my well pump. Both pairs were tied together so you could turn them on or off together - the mechanism tying them together was identical to the ones used on these Eaton's BQ220230 and BQC220230

After doing a ton of reading online I still have 3 specific questions:

1) I've read that these handles are for convenience (so you can turn them both on or off at the same time), and that they do NOT make the breaker in to a common trip breaker (i.e. even with the handles you can still have one side of a pair trip without causing the other to trip). I did see a thread here though, indicating that someone should add these handles to create a common trip. Is this correct? The handles tying each pair together do, or do not create a common trip?

2) The breaker I'm replacing was labeled independent trip, and I see common trip models are available (the BQC varient mentioned above). Why wouldn't I want common trip? The failure I had was only one of the dryer breakers tripping (this was sort of ok because the dryer would work, it just wouldn't get hot). If this happened to my pump circuit though, wouldn't running it at 120v damage it? Is there any reason I don't understand that would make me want to use independent trip instead of common trip?

3) Last, I just wanted to confirm that for the BQC common trip mentioned above. The 'common' only applies to the other side of the same pair, and not to the other pair. I.e. if the top trips (dryer) it will also trip the bottom (dryer), but not trip the two centers (pump).

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Addressing your points in turn:

1) Handle ties do not make a BR breaker pair common trip (2-pole BR breakers have an internal common trip mechanism) -- see footnote 2 on page 84 of Eaton's catalog.

2) Common trips are generally used in 240VAC circuits -- while what the previous installer did with the pump circuit is not wrong as per the 2014 NEC 240.15(B)(2):

Grounded Single-Phase Alternating-Current Circuits. In grounded systems, individual single-pole circuit breakers rated 120/240 volts ac, with identified handle ties, shall be permitted as the protection for each ungrounded conductor for line-to-line connected loads for single-phase circuits.

common trips are generally used on all 240VAC circuits (it's hard to get a non-common-trip 240VAC breaker in a typical form factor), and are needed in mixed 120/240VAC circuits for the reason you observed, as per NEC 240.15(B):

Circuit Breaker as Overcurrent Device. Circuit breakers shall open all ungrounded conductors of the circuit both manually and automatically unless otherwise permitted in 240.15(B)(1), (8)(2), (B)(3), and (B)(4).

(The exemption in (B)(1) is for multiwire branch circuits serving only 120VAC loads, while (B)(3) and (B)(4) are irrelevant to residential practice.)

3) You are correct -- this is documented pictorially in the table headings on page 82 of the Eaton catalog, so it's easy to miss.

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