On Nov 6, 12:53*pm, "Existential Angst"
wrote:
"dpb" wrote in ...
Existential Angst wrote:
Awl --

A two-part Q:

Due to some remodeling, I'm forced to splice/lengthen some old bx cable
that has #14 wire in it, and re-connect to the fuse box.
Should I splice the #14 with #14, or splice with #12?

The reason I would continue with #14 wire is just to remind me and future
people that Hey, this old wire is a little lighter than modern #12, and
to not take liberties with 20 or 30 amp fuses or breakers. *Other than
that, #12 would be fine with me.

There's nothing "unmodern" about 14 for 15A circuits.

Really? *Does the NEC state that?

I thought #12 was the de-facto "standard" for wiring, but mebbe that was
just NYC in its oppressive heyday, before it relented and went with the NEC.
In that heyday in NYC, * 20 A breakers were illegal on #12 wire! *Altho
after inspection, few people adhered to that limit.

What is the max breaker allowable on #14 and #12 wire with modern
insulation, nowadays?
Ditto, with cloth insulation?



I'd recommend sticking w/ same gauge as the original circuit for the
reason mentioned.

Remember to not bury connections in inaccessible places.

Indeed!



Next, *is there a rule of thumb for how many hot wires can share one
neutral of the same gauge? *If using different gauges, is there a "gauge
ratio", ie, some formula for cross sectional area between total hots and
total neutrals?

Don't follow this question. *Each hot needs its own return neutral.
If you're talking about 3-wire ("Edison") circuits, if properly wired the
return is in effect a neutral w/ a balancing currents from the two sides
if both are loaded equally; hence only the same size conductor is required
for a single-sided load.

If that isn't it, I have no clue what you're thinking.

I think you answered the Q: *If each hot *in a 3-wire bx *is connected to a
different leg in the panel, then they can share a common equal-sized
neutral. *So the "ratio" would be 2:1.

Which is why the neutral in main service can be "de-rated" rel. to the hots,
because the assumption is that there will in fact be some balancing of the
load between the two legs in "Net usage", reducing the demand on the
neutral.


The neutral is not derated in the service. Let's take a 200 amps
service. ALL the conductors in the service cable are rated for 200
amp capacity because that is the max current you can have flowing in
them. If it's a pure 240volt load of 48KVA or a balanced 120volt
load of 48KVA, then 200 amps is flowing in the two hots, zero in the
neutral. If it's a 120volt unbalanced load, then 200 amps is flowing
between one hot and the neutral.

Gee, seems I recall having this discussion here before.....




In a worst case scenario -- full load occurring on only one leg -- then the
neutral proly should be equal in gauge to the hot gauge. But statistically,
esp. in large buildings, this is unlikely.
*iirc, the svc neutral to large buildings can be smaller than the gauge of
either hot leg, but I wouldn't bet the farm on my memory.
--
EA





--- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -