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?

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bud--