"bud--" wrote in message
.. .
John Grabowski wrote:

I've posted on aspects of this before, and d-day is coming.

The situation is this:
A fuse panel upstairs is being eliminated, and the #14 bx cable
extended down about 10-15 feet to a new surface mounted breaker panel
downstairs. Thirteen separate bx cables, 7 of which are 3 wire (Edison),
for a total of 20 circuits.

Should I extend each bx cable with its own extension bx (or romex), or
get one or two 3/4-1" greenfield cables with sufficient #14 conductors
pulled through?

I'm leaning toward the greenfield, as it's just neater, less bulky,
fewer knock-out connections, and I believe a lot more economical.

Opinions? Pros/cons of either strategy?



*I'd go with 3- 3/4" or 2-1" flexible conduits since you will have a
total of 33 conductors plus a grounding conductor in each conduit. Using
the conduits will make it easy to pull additional circuits in the future
if needed. Single conductor wire is cheaper than BX cable.

Check tables C.3, 310.15(B)(2)(a) and 310.16 for more information.

310.16 gives the allowable "ampacity" for the wire. Assuming it is #14
with *THHN* insulation the ampacity is 20A (but cannot be used at over
15A).

310.15(B)(2)(a) requires the ampacity to be reduced if there are more than
3 wires in a conduit. If you have 6 "current-carrying" wires, the ampacity
is reduced to 80%. For #14 *THHN* the ampacity is then 16A and you can
still use it on a 15A circuit. You can not have more than 6
"current-carrying" #14 *THHN* wires in a conduit and connect them to a 15A
breaker.

310.15(B)(4) says that the neutral of a 3 wire "Edison" circuit does not
count as one of the "current-carrying" conductors.

310.15(B)(5) says that ground wires do not count as "current-carrying"
conductors.

You can run 3 "Edison" circuits, 9 - #14 *THHN* wires (6
"current-carrying" conductors) in a single conduit. Add a #14 ground wire.

Appendix C.3 says the 10 - #14 conductors can be run in a 1/2" Greenfield
(aka flex).

For 2 wire circuits (if you do not combine them to be "Edison" circuits),
you can run 3 - #14 *THHN* circuits in the same conduit - 6
"current-carrying" wires plus ground = 7 wires.

The rules are somewhat more complicated, but this is what should apply to
what you are doing, assuming the installation complies with the NEC.

Since you are posting fairly often, do you have a copy of the NEC?
Are you reasonably proficient at reading it?

Very helpful info, thank you.
I have a 1996 NEC, and I *could* be proficient at reading it if the
essentials weren't drowned in thousands of other words. But yeah, the
tables in App. B and C do get to the point.

It seems that many others have trouble reading the NEC, as there is a whole
cottage industry of workbooks and guides in how to read, understand, and use
the NEC. wow....

I just came home with 100 ft of 3/4 greenfield, two 500 ft rolls of #14
wire -- which, btw, just jumped $5 a roll in the past 3 days. Man, I hate
gving money to HD -- who nevertheless charge in some cases quite a bit less
than electrical supply houses for wire -- but a hair more for greenfield.
--
EA


--
bud--