On Wed, 27 Jan 2010 09:19:12 -0500, Ned Simmons wrote:

On Wed, 27 Jan 2010 20:00:04 -0800, jk wrote:

Ned Simmons wrote:



310.4 Conductors in Parallel.
(A) General. Aluminum, copper-clad aluminum, or copper
conductors of size 1/0 AWG and larger, comprising each
phase, polarity, neutral, orgrounded circuit conductor shall
be permitted to be connected in parallel (electrically joined
at both ends).

I read that to mean you can run 1/0 and larger conductors in parallel
if they're run together. 12 ga romex daisy-chained around the
perimeter of a room with both ends tied to the breaker would be (1)
too small and (2) not "within the same raceway, auxiliary gutter,
cabletray, cablebus assembly, trench, cable, or cord."


The question is, is a "ring" really parallel conductors. I could
argue it either way.

I suppose you could argue that they're not physically parallel, but
the parenthetical at the end of 310.4(A) anticipates that quibble when
it says, "parallel (electrically joined at both ends)." Or do you
have something else in mind?


Since the thing started off talking about the UK ring-main circuit, there is
an additional bit of information that adds weight to your code stipulations:-

There have been two standards in the UK for industrial plugs and sockets:-

BS196 AKA Reyrolle. This standard is pretty-well obsolete, but still
permitted. It has non-reversible plugs that have either one fuse, for circuits
with line and neutral (at earth voltage) or two fuses for circuits with two
lines. The fuses are effectively the pins of the plug. This system allows
circuits to be radial or ring in topology with no limit on the number of
sockets.

BS4343 AKA Commando. This standard is current and commonly used for 110V,
240V, 415V three phase (4 or 5 wire). It has non-reversible plugs, specified
colours and keying for different voltage systems and has no fuse in the plug.
No limit on the number of sockets, but circuit must be radial.

It might be local prejudice, but compared with current UK plugs and sockets,
all of the US NEMA connectors I've seen, from NEMA 1 to the NEMA twist-lock
series, look as if they were designed by a suicidal school dropout!

Ignoring that un-called for comment. The point of the post is that it seems
that ring circuits should only be used where you have fusing at each
individual connection. If the plugs or receptacles don't have their own fuses,
a radial circuit is preferred.


regards
Mark Rand
RTFM