On Wed, 08 Dec 2010 15:13:53 -0800, Larry Jaques
wrote:

On Wed, 08 Dec 2010 14:39:26 -0800, Mike M
wrote:

On Tue, 07 Dec 2010 20:17:50 -0800, Larry Jaques
wrote:

On Tue, 07 Dec 2010 13:16:11 -0500, wrote:

On Mon, 06 Dec 2010 23:02:40 -0500, Bill wrote:

Scott Lurndal wrote:
writes:

To avoid "cycling the breakers", Lew advised running 12-3 from two 20
Amp breakers (it would not have occurred to me to do that).

I'm not sure what this means, but if you're running two 120v circuits
using 12-3 from a pair of 20A breakers, make sure the breaker handles
are tied together such that both trip if either one trips.

scott

Because???

Because 1) - it is code.

Show me code in any country which demands tied circuit breaker handles
for 120v circuits. I double dog dare you!


2) if one circuit trips and you assume the wire is "dead" you
could be - the black could be dead, and the red live, and a lifted
neutral (which is common to both) would be LIVE.

We're talking 120v here, not 240, clare. With 240v, both phases are
going to the same box. Here, there are separate circuits and boxes
with a single phase going to each.



210.4 Multiwire Branch Circuits.
(A) General. Branch circuits recognized by this article
shall be permitted as multiwire circuits. A multiwire circuit
shall be permitted to be considered as multiple circuits. All
conductors of a multiwire branch circuit shall originate
from the same panelboard or similar distribution equipment.
FPN: A 3-phase, 4-wire, wye-connected power system
used to supply power to nonlinear loads may necessitate
that the power system design allow for the possibility of
high harmonic currents on the neutral conductor.
(B) Disconnecting Means. Each multiwire branch circuit
shall be provided with a means that will simultaneously
disconnect all ungrounded conductors at the point where
the branch circuit originates.
(C) Line-to-Neutral Loads. Multiwire branch circuits
shall supply only line-to-neutral loads.
Exception No. 1: A multiwire branch circuit that supplies
only one utilization equipment.
Exception No. 2: Where all ungrounded conductors of the
multiwire branch circuit are opened simultaneously by the
branch-circuit overcurrent device.
FPN: See 300.13(B) for continuity of grounded conductor
on multiwire circuits.
(D) Grouping. The ungrounded and grounded conductors
of each multiwire branch circuit shall be grouped by wire
ties or similar means in at least one location within the
panelboard or other point of origination.
Exception: The requirement for grouping shall not apply if
the circuit enters from a cable or raceway unique to the
circuit that makes the grouping obvious.
ARTICLE 210€”BRANCH CIRCUITS 210.4
2008 Edition NATIONAL ELECTRICAL CODE

Mike, can you point out the particular text in that extract which
states the demand to tie two 120v breakers together when supplying
120v equipment?


B) Disconnecting Means. Each multiwire branch circuit
shall be provided with a means that will simultaneously
disconnect all ungrounded conductors at the point where
the branch circuit originates.