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Wayne Whitney

On 2008-08-25, wrote:

Sorry if this is a dumb question: if they are physically tied
together with a tie bar, and (somehow) a single breaker trips, will
the trip throw the switch hard enough to force the other breaker to
switch off together with it??

No, not always. There's a difference between a double pole breaker,
where the two sides are internally connected, and two single pole
breakers with a handle tie. In both cases, if you manually turn off
the breaker (you are using it as a disconnect), you will turn off both
sides. But as far as automatic operation (its job as an overcurrent
protection device), only the double pole breaker will reliably shut
off both sides.

For the OP, you need at a minimum to have the proper handle tie (no
nails!), and you may need to have a double pole breaker. I believe
that if the pump uses the neutral, you need a double pole breaker; if
it is a pure 240V load without using the neutral, then a handle tie is
sufficient. I've quoted the appropriate parts of the NEC below (2002
version). I'd just put in a double pole breaker, anyway, as it seems
safer.

Cheers, Wayne

240.20(B) "Circuit Breaker as Overcurrent Device." Circuit breakers
shall open all ungrounded conductors of the circuit unless otherwise
permitted in 240.20(B)(1), (B)(2), and (B)(3).

240.20(B)(2) "Grounded Single-Phase and 3-wire dc Circuits." In
grounded systems, individual single pole circuit breakers with
approved handle ties shall be permitted as the protection for each
ungrounded conductor for line-to-line connected loads for single-phase
circuits or 3-wire, direct current circuits.

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