Hi all,

This is a code question more than anything, but I thought it might be
worth looking at.

I recently had a 240V electrical heating circuit added. #12 wire, 20A
breaker. Max load is 3840W, but I want to drive 4500W.
Unfortunately, 25A breakers aren't available for my panel (this would
fix the problem) and I have no additional circuits left in my panel.

One other solution is to use 30A breakers and switch to #10 wire.
Problem is that one heater was already in-place (and on a different
floor) so I'd have to demolish the house to re-wire it. Is it
acceptable to run #10 wire from the panel to the first thermostat
(3000W), and keep the existing #12 wire for the remaining 1500W (which
is branched from the first thermostat)?

Under normal conditions, current will never exceed wire maximums.
However, if the 1500W heater had a fault, current through that section
could potentially exceed the #12 capacity (30A) before tripping.
Doesn't sound safe to me, but I wonder if there is anything in the
code that would allow it.

FWIW, I have an alternate solution that will balance loads between
heating circuits..it just isn't pretty because I need to create (and
maintain access to) a junction in an existing circuit.

Borrall Wonnell wrote:
....

I recently had a 240V electrical heating circuit added. #12 wire, 20A
breaker. ...

....
... Is it
acceptable to run #10 wire from the panel to the first thermostat
(3000W), and keep the existing #12 wire for the remaining 1500W (which
is branched from the first thermostat)?

....

In a word, "No" (assuming you're intending to switch to a 30A breaker
which your posting doesn't explicitly state but I infer is the reason
for posing the question).

--

wrote in message
...
On Thu, 9 Dec 2010 10:27:58 -0800 (PST), Borrall Wonnell
What you suggest is probably safe (#10 to the stat #12 to a 1500w
heater) but it is not legal.
Arguing on the safety side I can say the 1500w load is well within the
ampacity of the 12ga wire and a short will still safely be cleared by
a 30a breaker.

A short circuit will trip breakes with much smaller wire than the code
requires. That is only part of the problem. If there is a wiring problem
that causes the smaller wire to draw more current, but not enough to trip
the larger breaker, the wire can over heat and causes a fire.

On Dec 9, 1:27*pm, Borrall Wonnell wrote:
Hi all,

This is a code question more than anything, but I thought it might be
worth looking at.

I recently had a 240V electrical heating circuit added. *#12 wire, 20A
breaker. *Max load is 3840W, but I want to drive 4500W.
Unfortunately, 25A breakers aren't available for my panel (this would
fix the problem) and I have no additional circuits left in my panel.

One other solution is to use 30A breakers and switch to #10 wire.
Problem is that one heater was already in-place (and on a different
floor) so I'd have to demolish the house to re-wire it. *Is it
acceptable to run #10 wire from the panel to the first thermostat
(3000W), and keep the existing #12 wire for the remaining 1500W (which
is branched from the first thermostat)?

Under normal conditions, current will never exceed wire maximums.
However, if the 1500W heater had a fault, current through that section
could potentially exceed the #12 capacity (30A) before tripping.
Doesn't sound safe to me, but I wonder if there is anything in the
code that would allow it.

FWIW, I have an alternate solution that will balance loads between
heating circuits..it just isn't pretty because I need to create (and
maintain access to) a junction in an existing circuit.

Have you looked at possibly swapping out some of your other breakers
with a few of those single slot, double breakers to create some more
room in your box.

http://cdn.oneprojectcloser.com/wp-c...aker-panel.jpg

On Dec 13, 1:29*am, wrote:
On Thu, 9 Dec 2010 10:27:58 -0800 (PST), Borrall Wonnell
I recently had a 240V electrical heating circuit added. *#12 wire, 20A
breaker. *Max load is 3840W, but I want to drive 4500W.
Unfortunately, 25A breakers aren't available for my panel (this would
fix the problem) and I have no additional circuits left in my panel.


According to the code, this is NOT legal. *It's also a fire hazzard.


Update:
I went with the cheapest solution. I swapped two of my 500W heaters
for 300W units and transferred one of them to another heating
circuit. Both circuits are now loaded at 3800W, just below the 80%
limit. This required one extra junction box and 30' of wire, but the
heaters were a couple of bucks cheaper. On the downside, I have
absolutely no headroom for future expansion. If the next owner wants
to put in that hottub (or whatever), he'll have to pay dearly for
it