[PVRCNC] 12AWG =30 amp?

[Tom Gallagher]

Sorry it took so long to get back in.... I've been snowed under, and just
haven't checked this email lately.

First, the "definative source" will ALWAYS be your local permits &
inspections. Period, the end.
The next authority is the homeowners insurance company. A good example is
this: Knob-and-Tube wiring is OK by inspections (some say "it's the best
there is") but my insurance carrier won't insure it. Guess who re-wired
the entire house (built in 1910).

NOW... the guide to pleasing the inspections department is the National
Electrical Code (NEC). Don't look too hard for a copy on the web. It's
copyrighted by NFPA. However, the allowed ampacity is generally outlined
in NEC Table 310-16. See it here:
http://www.armstrongssupply.com/wire_chart.htm    Generally, the left side
is for copper conductors, the right is for aluminum. The individual
columns are for the insulation.... you'll most like buy THHN/THWN these
days. UF is "underground feeder" and RHW and USE are generally individual
strands.

By now, if you've looked at the table, you'll have noticed that 10-12-14
AWG wire has table entries significantly higher than what you'll find them
used for. Please notice, in the far left column, that there is a footnote
reference. Read the foot note; it trumps everything.

"...1 The load current rating and the overcurrent protection for conductor
types shall not exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG, and
30 amperes for 10 AWG... " Yes, I know if you read it, it sounds like it's
only applied to aluminum cable, but the people who wrote this were
electricians, not English majors. #14 = 15 amps.  #12 = 20 amps. #10 = 30
amps. You can always use a lower-value breaker, but never higher. An
example of this is if you air conditioning condensor say "max CB 25 Amps"
and you run #10 wire and protect with a 25 amp breaker

Returning to your original question.... yes, #12 will handle 30 amps fine,
especially if it's THHN insulation. If you're only talking three feet or
so, it won't lose enough power to heat to notice. However, it isn't the
best practice.

Have fun.

73  de tom n4ioz.

alsopb wrote:

> Guys,
>
> Ran across something odd while planning the install of a programmable
> timer for hot water heater.  Looking for comments.
>
> 1) Circuit breaker box shows dual 30 amp breakers (well not quite--see
> below)
> 2) Heater element rating 4.5Kw (19 amps).
> 3) Wire gauge at heater = #12
>
> This looks goofy to me.  Also upon close inspection one of the 30 amp
> ganged circuit breakers is marked (faded and hard to read) 50 amp!
>
> I would have expected #10 wire to the hot water heater. It does appear
> that #12 wire would carry the load OK and the run is short.  But why a
> 30 amp breaker?  Possibly to handle a brief high current condition
> when the heating element is cold?  For what it is worth, there is no
> evidence of overheating of the wire insulation either at the breaker
> or water heater.
>
> By the way, there seems to be considerable confusion on how much
> current handling capacity #12 wire has in romex.  I see numbers out
> there from 20 to 27 amps.  Anybody got a definitive source.
>
> The timer I've found mounts in a standard switch box and is the size
> of a ground fault interrupter. I'll be able to expand an existing
> outlet box right next to the breaker panel to accommodate it.  It has
> its own clock (digital) battery backup in addition to non-volitile
> memory for the on/off cycle.  It will drive big relay in the the
> circuit breaker panel.  Will be a nice neat installation.  Won't have
> to climb under the house to bypass or reset as would be the case in a
> standard timer installation.
>
> 73 de Brian/K3KO
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