In article , "Twayne" wrote:
EXCELLENT link, Doug! I've often searched for a cohesive presentation of the
NEC and never found it

In that case, you haven't searched very hard; the NEC has been online at least
since the 2002 version, and links have been posted in this newsgroup
repeatedly. Any of the major chain bookstores (Barnes&Noble, Borders, etc)
will have a copy in stock or be able to order one. You can buy it directly
from the NFPA. There are copies on eBay. You can buy it from Amazon.

Since you have as good as admitted that you haven't read it, perhaps you can
understand why nobody takes you seriously when you proclaim your misconceived
notions as fact -- and why I keep telling you to stop giving electrical
advice: you don't know what you're talking about.

; only pieces here & there and those never allow you
to check into the outside references, etc.. I definitely appreciate it as
I'm sure others do and it definitely gives you a top-credibility rating.

Now that you know where the Code is, you no longer have any excuse for not
knowing what it says.

It does provide verification, IMO, that one overloaded ckt on one leg and
very light load on the other, under fault conditions on the first leg, could
cause overheating and other unforeseen problems,

It does nothing of the kind. Overloading either leg will trip the breaker and
disconnect both legs.

especially in a miswired
case.

You mean, *only* if miswired.

In theory equal loads on each leg will result in zero current flow in
the neutral, which is as I understood it.

Correct. Unfortunately, that is the *only* thing you got right.

It does still appear though, that a fault on one leg and little load on
the other could result in substantial current flow, then adding the fault
conditions ... .

It appears that way only because you don't understand how it works. In a
properly wired Edison circuit, the current in the neutral can never exceed the
current in *one* hot leg.

These following aren't critical questions at the moment so feel free to
ignore them if you find them intrusive:

1. One thing is confusing however, that you might be able to explain. In
Definitions (100) for Branch Ckt, Multiwire, it states that:
"... branch ckt that consists of two or more ungrounded conductors that have
a voltage between them, and a grounded conductor that has equal voltage
between it and each ungrounded conductor of the ckt and that is connected to
the neutral or grounded conductor of the system"

Yes....

It _seems_ to say the voltage between the two ungrounded conductors and the
neutral will be at the same potential as the ungrounded connectors?

No, it neither says that, nor "seems to". There is absolutely *nothing* in
that paragraph to indicate, imply, or suggest that. In fact, it means exactly
the opposite: that they will *not* be at the same potential WRT each other as
each is WRT the neutral.

I seem
to have a brain-freeze again! Can you clarify what that means?

One clause at a time:

"branch circuit that consists of two or more ungrounded conductors" = a branch
circuit having two or more hot wires

"with a voltage between them" = each of the hot wires is on a different leg of
the service (if they were on the same leg, there would be no voltage between
them)

"and a grounded conductor" = and a neutral wire

"that has equal voltage between it and each ungrounded conductor of the
circuit" = voltage between the neutral and each hot wire is the same as
between the neutral and every other hot wire

"and that is connected to the neutral or grounded conductor of the system" =
the circuit neutral must be grounded at the panel.

The
following ref to "neutral or ungrounded conductor of the system" seems to
make no sense then and obviously it has to.

And you accuse trader4 of having reading comprehension problems -- !

It doesn't say that. It says "neutral or GROUNDED conductor" -- which makes
perfect sense to anyone who understands residential electrical wiring.

2. I've never actually had my hands on a double pole breaker

Yet you consider yourself competent to comment on what types of circuits may
or may not be used with them, and the relative safety thereof.

Amazing. Simply amazing.

and Google
hasn't given me the answer to this one: Are the breakers still independent
of each other?

No, of course not. They are mechanically connected with a handle tie; some
also are connected internally ("internal common trip"). If they were
independent, it wouldn't be a double-pole breaker. It would be two single-pole
breakers.

I don't think that makes sense so, assuming I'm right, how is it that an
overload on one isn't affected (delayed, held from tripping) by the force
the other needs to be opened?

It trips with ample force to bring the other one along with it, even if the
only connection is an external tie.

Move a breaker handle from the 'off' position to the 'on' position; notice how
much force you have to apply to it. Now nudge it from 'on' to 'tripped' -- see
how easy that was, and how forcefully it snaps over? More than enough to
trip a second handle tied to it.

I thought maybe there was a different internal
structure somehow and they were electonically opened somehow, but I can't
find proof of that either. I did find one page (crecibility unknown) that
said both breakers operated simultaneously,

I guess that depends on what kind of time lag you would consider
"simultaneous". In the case of an internal common trip, they would in fact
trip simultaneously. With an external handle tie, there must be some tiny lag
due to mechanical play in the connection, but it's very small.

but without internal electronics
of some sort I can't see how the drag from one doesn't affect the other?

The effect is minuscule.

Thanks again for the very valuable lead,

Like I said -- now that you know where the Code is, you no longer have any
excuse for being ignorant of it, or dispensing clueless advice that
contradicts it.