In article , "Existential Angst" wrote:
"Doug Miller" wrote in message
...
In article , "Existential Angst"
wrote:
"David Nebenzahl" wrote in message
ers.com...

Do you know *why* you can use just one neutral to serve two hots with
this kind of circuit?

If I didn't, would you tell me?

Apparently you don't, so permit me to enlighten you. Code requires that all
ungrounded (i.e. hot) conductors of a multiwire (Edison) circuit have a
*single* disconnecting means -- so unless you can find a 20-pole breaker,
you're going to have a tough time meeting Code with that monster circuit
you proposed.

The reason Code requires this is straightforward: the neutral wire carries
current. If one hot leg of a multiwire circuit is left powered on, and any
load on that leg is in use, the current drawn by that load is flowing in the
neutral -- presenting a risk of fatal electric shock to anyone servicing the
other leg of that circuit.

So are you saying that in a simple 3 wire bx cable, with the two hots
sharing a neutral, you'd need a two-pole breaker?

Correct -- not only for the reason I cited above, but also for another reason
which has already been discussed in this thread: to ensure that the two hots
are on opposite legs of the service.

If the two hots are on the *same* leg of the service, then the neutral could
be overloaded, because it will carry the *sum* of the currents in the hot
wires. This is a fire hazard.