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.

Wayne Whitney wrote:
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.


What breakers, other than a main, are 'tied' internally? I've never seen
one.


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.

Whats the electrical difference between a double pole breaker and 2
breakers with the handles tied together? We are not talking about a
double pole switch where the hots and neutral are all switched are we?

Kevin



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.

On 2008-08-26, Kevin Ricks wrote:

Whats the electrical difference between a double pole breaker and 2
breakers with the handles tied together?

The difference is that in a 2 pole breaker, the trip mechanisms are
tied together internally and will both trip if the unit sense an
overcurrent. For two single breakers with a handle tie, this is not
reliably true.

Wayne

In article ,
Wayne Whitney wrote:

On 2008-08-26, Kevin Ricks wrote:

Whats the electrical difference between a double pole breaker and 2
breakers with the handles tied together?

The difference is that in a 2 pole breaker, the trip mechanisms are
tied together internally and will both trip if the unit sense an
overcurrent. For two single breakers with a handle tie, this is not
reliably true.

Wayne

Curious minds want to know why tying the trip mechanisms together
internally is intrinsically safer or more reliable than tying them
together externally.

On 2008-08-26, Smitty Two wrote:

Curious minds want to know why tying the trip mechanisms together
internally is intrinsically safer or more reliable than tying them
together externally.

Have you used a handle tie? There's some give. Wayne

In article ,
Wayne Whitney wrote:

On 2008-08-26, Smitty Two wrote:

Curious minds want to know why tying the trip mechanisms together
internally is intrinsically safer or more reliable than tying them
together externally.

Have you used a handle tie? There's some give. Wayne

I've not used them. Odd that they would make them poorly. Good to note
that it's the execution and not the theory that's at fault, then.

On 2008-08-26, Smitty Two wrote:

Have you used a handle tie? There's some give. Wayne

I've not used them. Odd that they would make them poorly. Good to
note that it's the execution and not the theory that's at fault,
then.

It's not that handle ties are made poorly, it is that circuit breakers
have two (or more) functions: they can serve as a manual disconnect
and they can serve as an overcurrent protection device. Handle ties
only have to do with the function as a manual disconnect.

If you think about it, a circuit breaker has three states: on, off,
and tripped. Often to reset a circuit breaker you need to go from
tripped to off to on. As a result, the handle isn't rigidly connected
to the internal trip mechanism. So the handle tie can't rigidly
connect the trip mechanisms.

Cheers, Wayne