ECN Forum Forums Code Related Discussion NEC & other Code issues 277 on a 480 breaker

JBD, I'd really like more detail on that quotation. That's why I asked. My copy of the "White Book" seems to say just the opposite.

Form the 2006 edition, page 45, under 'circuit breakers (DIVQ):'

"Single pole or multi-pole independent trip circuit breakers, with or without handle ties, 120/240V ac, are suitable for use in a single phase, multi-wire circuit on line-to-neutral connected loads."

There then follows many similar statements applying to a variety of different circumstances. To be fair, though, I must admit that none of the circumstances specifically address 480/277 systems. The section does, however, go on to say that the category includes all breakers for less than 600 volts.

I did find a quote like yours ... but that was in a specific discussion of a multi-pole breaker that was marked "no common trip" or "independent trip.: (Marking guide, "Molded Case Circuit Breakers," paragraph 39.) That this is contradicted by the general provisions of the breaker category, and is in a discussion of a specific circumstance .... leads me to conclude that the restriction applies only to that specific circumstance.

Line to neutral loads do not require a common trip. Common switching is all that is required for multi-wire branch circuits that serve only L-N loads.

Line-Line loads do require common tripping, which means that an external handle tie only is not sufficient.

Again ... the section I cited also refers to line to line loads, and the handle tie being adequate.

I believe that the multiplicity of circuit types is detailed for the 'lower voltage' arrangements simply because of one that is NOT listed: the 240 Delta. Such panels ought not have any single pole circuits in them.

Here's the paragraph right after the one I quoted:
"Single pole or multi-pole independent trip circuit breakers, with handle ties, rated 120/240 v ac, are suitable for use on multi-wire circuits with line-to-line or line-to-ground connected loads."

As mentioned, that's the text of the White book itself; I'm still confused as to what the "Marking guide" is discussing.

No matter how you slice it, the White book is pretty specific in stating that handle ties DO qualify as a disconnecting means.

Looks like my terminology is backwards.

From NEMA AB-3 2001 (para 3.1.5) a multi-pole breaker normally has an internal common trip and a two-pole breaker may have an independent trip.

The UL White book DIVQ says that independent trip units may be used on MWBC that include a grounded neutral even if there are L-L loads. But it goes on to say that multi-pole common trip devices may be used with L-L circuits that do not have a neutral.

What do you expect when engineers try to write? Neither UL nor NEMA publications are either very readable or arranged to let you find stuff

For reference, US Navy uses mil-spec breakers exclusively. Really nice strong ones, the kind that won't trip just because the case is hit with a sledgehammer (or the ship by a torpedo, which has much the same effect). They still won't work underwater, but that's OK because the panels are watertight.

Anyhow, small sizes are typically acquisitioned in single-phase units, which are all retrofitted using field-installed 2 or 3-handle yokes. Not saying this is necessarily allowed by UL, but DoD is a widely recongized listing agent, too, and it clearly works just fine for the DoD.

To throw something else into the mix, don't forget that there are two pole breakers that have a common trip handle, which is what I have in this situation. If it's ok to use only one leg of the breaker, is it not then ok to use the other leg for another circuit, especially since I have a common trip handle?

I don't see why that would be a problem. It's not different than any other multiwire shared-neutral circuit, aside from a very short length of shared neutral.

Rather inconvenient from an end-user perspective, though.