This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. The other heaters
are 750 watt, wired 240, and draw 2.7 amps each. The circuit is 30
amps, so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.

I was surprised to find the wire to the circuit I planned to pony from
was a 14/2. I traced it back to the junction box, and found each of
the heaters was serviced by a 14 gauge wire. Then I was horrified to
find that the wire from the panel to the main junction box for all
circuits was also a 14 gauge. Even at low amperage, I would expect at
least a 12 gauge, maybe 10?

So, I have shut off the circuit pending some advice on how to wire it
safely. I expect my options are :

1 - Panel-Junction box 10 gauge. Junction box to each heater 12
gauge.
2 - Panel-junction box 12 gauge. Junction box to each heater 12
gauge.
3 - Panel- junction box 12 gauge. Junction box to each heater 14
gauge.

The final load on the circuit at 240V will be about (if all was on at
full blast) 13.5 amps. We have never turned on any more than two of
the heaters, but I am pretty sure the proper calculation would require
the worst case scenario.

Can anybody tell me what the best wiring combination is? I will ask
my electrician to do the final connection of the panel to the junction
box, but I would like to have the wiring from the junction box to the
heaters in place to save some bucks.

tnx in advance

gwandsh wrote:
This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. The other heaters
are 750 watt, wired 240, and draw 2.7 amps each. The circuit is 30
amps, so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.

I was surprised to find the wire to the circuit I planned to pony from
was a 14/2. I traced it back to the junction box, and found each of
the heaters was serviced by a 14 gauge wire. Then I was horrified to
find that the wire from the panel to the main junction box for all
circuits was also a 14 gauge. Even at low amperage, I would expect at
least a 12 gauge, maybe 10?

The existing circuit is fine with 14 ga wire (but it should have a
15A breaker or fuses, not 30A). You can load it up to 12A, because
resistive heating circuits are limited to 80% of their ampacity --
so adding a 1000W heater (14 guage wire is good enough) takes you
pretty close to the limit but you're still under.

Make sure that the breakers or fuses are the right size for the
wires -- 15A. This is important. The rest, not so much.

Bob

wrote:
On Sat, 24 Oct 2009 22:37:59 -0700 (PDT), gwandsh
wrote:

This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. The other heaters
are 750 watt, wired 240, and draw 2.7 amps each. The circuit is 30
amps, so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.

I was surprised to find the wire to the circuit I planned to pony from
was a 14/2. I traced it back to the junction box, and found each of
the heaters was serviced by a 14 gauge wire. Then I was horrified to
find that the wire from the panel to the main junction box for all
circuits was also a 14 gauge. Even at low amperage, I would expect at
least a 12 gauge, maybe 10?

So, I have shut off the circuit pending some advice on how to wire it
safely. I expect my options are :

1 - Panel-Junction box 10 gauge. Junction box to each heater 12
gauge.
2 - Panel-junction box 12 gauge. Junction box to each heater 12
gauge.
3 - Panel- junction box 12 gauge. Junction box to each heater 14
gauge.

The final load on the circuit at 240V will be about (if all was on at
full blast) 13.5 amps. We have never turned on any more than two of
the heaters, but I am pretty sure the proper calculation would require
the worst case scenario.

Can anybody tell me what the best wiring combination is? I will ask
my electrician to do the final connection of the panel to the junction
box, but I would like to have the wiring from the junction box to the
heaters in place to save some bucks.

tnx in advance


You are talking about 10.4a or so. (2500w @ 240v = 10.42a)
You do need to size at the smallest conductor on the circuit.
I would just put a 2 pole 15a breaker on that circuit and get on with
your life being perfectly legal.

Methinks OP is over in the UK, perhaps? Seeing as how he is running 240
on 14-2? They do some strange (by our standards) things with wiring over
there.

If OP is in UK, he may want to seek out that UK-centric DIY group to ask
in. I can't remember the name, but it has been mentioned on here before.

--
aem sends...

aemeijers wrote:

Methinks OP is over in the UK, perhaps? Seeing as how he is running
240 on 14-2? They do some strange (by our standards) things with
wiring over there.

If OP is in UK, he may want to seek out that UK-centric DIY group to
ask in. I can't remember the name, but it has been mentioned on here
before.

The OP is in Portland, Oregon (or environs).

He should have told us to avoid the confusion, but, in case of doubt, one
can look up his IP (76.115.41.158).

"gwandsh" wrote in message
...
This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. The other heaters
are 750 watt, wired 240, and draw 2.7 amps each. The circuit is 30
amps, so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.

I was surprised to find the wire to the circuit I planned to pony from
was a 14/2. I traced it back to the junction box, and found each of
the heaters was serviced by a 14 gauge wire. Then I was horrified to
find that the wire from the panel to the main junction box for all
circuits was also a 14 gauge. Even at low amperage, I would expect at
least a 12 gauge, maybe 10?

So, I have shut off the circuit pending some advice on how to wire it
safely. I expect my options are :

1 - Panel-Junction box 10 gauge. Junction box to each heater 12
gauge.
2 - Panel-junction box 12 gauge. Junction box to each heater 12
gauge.
3 - Panel- junction box 12 gauge. Junction box to each heater 14
gauge.

The final load on the circuit at 240V will be about (if all was on at
full blast) 13.5 amps. We have never turned on any more than two of
the heaters, but I am pretty sure the proper calculation would require
the worst case scenario.

Can anybody tell me what the best wiring combination is? I will ask
my electrician to do the final connection of the panel to the junction
box, but I would like to have the wiring from the junction box to the
heaters in place to save some bucks.

tnx in advance


I agree with Doug, the existing wiring is fine, with the exception of the 30
amp breaker. Replace it with a double 15, and keep your new wiring on a
separate 15 amp circuit

HeyBub wrote:
aemeijers wrote:
Methinks OP is over in the UK, perhaps? Seeing as how he is running
240 on 14-2? They do some strange (by our standards) things with
wiring over there.

If OP is in UK, he may want to seek out that UK-centric DIY group to
ask in. I can't remember the name, but it has been mentioned on here
before.

The OP is in Portland, Oregon (or environs).

He should have told us to avoid the confusion, but, in case of doubt, one
can look up his IP (76.115.41.158).


What can I say? Way too early in the AM to have thought of looking him
up. And as I often state, I'm no electrician, though I play one at
times. Haven't run across a lot of 2-wire 240 on small-gauge wire in
this part of the country. especially for heaters. (gas is usually a lot
cheaper around here.)
--
aem sends, going back to lurk mode on this thread....

In article , gwandsh wrote:
This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. The other heaters
are 750 watt, wired 240, and draw 2.7 amps each.

750W / 240V = 3.1A, not 2.7A.

The circuit is 30 amps,

Are you sure? A 15A double-pole breaker is a 15A 240V circuit, not 30A.

so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.

1000W / 240V = 4.2A, not 4.5A.

I was surprised to find the wire to the circuit I planned to pony from
was a 14/2. I traced it back to the junction box, and found each of
the heaters was serviced by a 14 gauge wire. Then I was horrified to
find that the wire from the panel to the main junction box for all
circuits was also a 14 gauge. Even at low amperage, I would expect at
least a 12 gauge, maybe 10?

14-gauge wire is perfectly fine for the existing load: 15A * 240V * 80% =
2880 watts, and you're using only 2250.

Adding another 1000 watts puts you over the limit, though.


So, I have shut off the circuit pending some advice on how to wire it
safely. I expect my options are :

1 - Panel-Junction box 10 gauge. Junction box to each heater 12
gauge.
2 - Panel-junction box 12 gauge. Junction box to each heater 12
gauge.
3 - Panel- junction box 12 gauge. Junction box to each heater 14
gauge.

None of the above. 1 is completely unnecessary; 2 works fine, but is much more
trouble than it's worth; 3 is a Code violation with either a 20A breaker
(because the 14ga wire is undersized for the breaker) or with a 15A breaker
(because the breaker is undersized for the load).

Instead, run a new 240V circuit, using 14ga wire and a new 15A double-pole
breaker, to supply the new heater, and make sure that the existing circuit
uses a 15A double-pole breaker as well. *Much* less effort than rewiring the
existing circuit.


The final load on the circuit at 240V will be about (if all was on at
full blast) 13.5 amps. We have never turned on any more than two of
the heaters, but I am pretty sure the proper calculation would require
the worst case scenario.

Yes, it would. This is the worst case: all four heaters drawing maximum
current for more than three hours, which meets the Code's definition of a
"continuous load" and therefore limits the circuit to 80% of its rated
capactiy. Three 750W heaters plus one 1000W heater = 3250W, or just over
13.5A, as you said. Eighty percent of 15A is 12A, so you need a 20A circuit
instead, and that means 12ga wire instead of 14. Don't waste your money on
10ga wire, though. There's no benefit.

In article , wrote:
On Sat, 24 Oct 2009 22:37:59 -0700 (PDT), gwandsh
wrote:

This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. The other heaters
are 750 watt, wired 240, and draw 2.7 amps each. The circuit is 30
amps, so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.
[...]

You are talking about 10.4a or so. (2500w @ 240v = 10.42a)

As I pointed out in another post, his numbers are wrong, but so are yours.
3 * 750W + 1000W = 3250W = 13.5A @ 240V.

You do need to size at the smallest conductor on the circuit.
I would just put a 2 pole 15a breaker on that circuit and get on with
your life being perfectly legal.

This would be good advice if your numbers were right. They're not, and he will
create a hazard if he adds that 1000W heater to the existing circuit.

In article , aemeijers wrote:

Methinks OP is over in the UK, perhaps?

His IP address indicates Portland, Oregon.

Seeing as how he is running 240 on 14-2? They do some strange (by our
standards) things with wiring over there.

There's nothing one bit unusual about running a 15A 240V circuit on 14-2. Why
do you think there is?

In article , zxcvbob wrote:

The existing circuit is fine with 14 ga wire (but it should have a
15A breaker or fuses, not 30A).

Right...

You can load it up to 12A, because
resistive heating circuits are limited to 80% of their ampacity --

Right...

so adding a 1000W heater (14 guage wire is good enough) takes you
pretty close to the limit but you're still under.

... and wrong, and wrong. Do the math. It takes him well *over* the limit, and
14ga wire is *not* "good enough".

3 * 750W existing + 1000W new = 3250W total = 13.5A @ 240V.

He needs 12ga if he's going to put all of them on the same circuit. It's
probably a lot easier to run a new 15A circuit on 14ga wire for the new heater
than it will be to rewire the existing circuit with 12ga.

"gwandsh" wrote

This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. The other heaters

I can't answer specifically being electrically challanged (grin), but i do
know when we had our sunroom install, we opted to have 2 of the outlets
direct to my under-utilized electrical service box. The house was upgraded
from 100 amp to 200 amp service about 15 years ago. The electricians smile
when they see the box as apparently we have oodles of excess there. Enough
to run plenty more outlets direct without 'sistering'.

Hence I have 2 outlets in the sunroom each on their own line, and a reserved
line set aside if we want to run a 240V back there for a powerful heater. I
don't know enough to say more other than we asked both be able to run
anything at the same time with a standard 3 prong plug such as an accessory
AC unit or accessory heater. Obviously we wouldnt be heating and cooling at
the same time, but you get the drift. I've used my 1500watt heater with no
problems. When it gets really cold, I also plug in (other outlet) the
monster radient heater to take the chill off fast.

This summer, we had an extra line run as well for the garage heater. Heats
400sqft, set at lowest to keep pipes from freezing. It's all on it's own
circuit too (GFCI not required but we did that for added safety as its other
side of the kitchen sink with water lines over it).

On Oct 25, 5:09*am, (Doug Miller) wrote:
In article , gwandsh wrote:

This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. *The other heaters
are 750 watt, wired 240, and draw 2.7 amps each. *

750W / 240V = 3.1A, not 2.7A.

The circuit is 30 amps,

Are you sure? A 15A double-pole breaker is a 15A 240V circuit, not 30A.

so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.

1000W / 240V = 4.2A, not 4.5A.



I was surprised to find the wire to the circuit I planned to pony from
was a 14/2. *I traced it back to the junction box, and found each of
the heaters was serviced by a 14 gauge wire. *Then I was horrified to
find that the wire from the panel to the main junction box for all
circuits was also a 14 gauge. *Even at low amperage, I would expect at
least a 12 gauge, maybe 10?

14-gauge wire is perfectly fine for the existing load: 15A * 240V * 80% =
2880 watts, and you're using only 2250.

Adding another 1000 watts puts you over the limit, though.



So, I have shut off the circuit pending some advice on how to wire it
safely. *I expect my options are :

1 - Panel-Junction box 10 gauge. *Junction box to each heater 12
gauge.
2 - Panel-junction box 12 gauge. *Junction box to each heater 12
gauge.
3 - Panel- junction box 12 gauge. *Junction box to each heater 14
gauge.

None of the above. 1 is completely unnecessary; 2 works fine, but is much more
trouble than it's worth; 3 is a Code violation with either a 20A breaker
(because the 14ga wire is undersized for the breaker) or with a 15A breaker
(because the breaker is undersized for the load).

Instead, run a new 240V circuit, using 14ga wire and a new 15A double-pole
breaker, to supply the new heater, and make sure that the existing circuit
uses a 15A double-pole breaker as well. *Much* less effort than rewiring the
existing circuit.



The final load on the circuit at 240V will be about (if all was on at
full blast) 13.5 amps. *We have never turned on any more than two of
the heaters, but I am pretty sure the proper calculation would require
the worst case scenario.

Yes, it would. This is the worst case: all four heaters drawing maximum
current for more than three hours, which meets the Code's definition of a
"continuous load" and therefore limits the circuit to 80% of its rated
capactiy. Three 750W heaters plus one 1000W heater = 3250W, or just over
13.5A, as you said. Eighty percent of 15A is 12A, so you need a 20A circuit
instead, and that means 12ga wire instead of 14. Don't waste your money on
10ga wire, though. There's no benefit.

Many thanks, and my apologies. I am actually in Oregon, but as you
can tell, not very electrical savvy. I rounded the amperage number of
the new heater fopr simplicity in my explanation.

It occured to me last night that the "paired" circuit breakers I saw
are indeed a 15 amp double poled circuit, rather than a 30 amp as I
reported. It wasn't until this "Eureka" moment that it all made
sense, and I appreciate all the feedback here.

I think I will return the 1000 watt heater (forget to get one with
thermostat anyways, yeesh), and get a 750 watt version. That one I
will pony off one of the existing heater sub-circuits. We have never
turned on more than one heater at a time at this place, and never even
close to max capacity (weekend summer application) so the circuit load
will never be an issue.

Again, thanks

On Oct 25, 5:09*am, (Doug Miller) wrote:
In article , gwandsh wrote:

This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. *The other heaters
are 750 watt, wired 240, and draw 2.7 amps each. *

750W / 240V = 3.1A, not 2.7A.

The circuit is 30 amps,

Are you sure? A 15A double-pole breaker is a 15A 240V circuit, not 30A.

so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.

1000W / 240V = 4.2A, not 4.5A.



I was surprised to find the wire to the circuit I planned to pony from
was a 14/2. *I traced it back to the junction box, and found each of
the heaters was serviced by a 14 gauge wire. *Then I was horrified to
find that the wire from the panel to the main junction box for all
circuits was also a 14 gauge. *Even at low amperage, I would expect at
least a 12 gauge, maybe 10?

14-gauge wire is perfectly fine for the existing load: 15A * 240V * 80% =
2880 watts, and you're using only 2250.

Adding another 1000 watts puts you over the limit, though.



So, I have shut off the circuit pending some advice on how to wire it
safely. *I expect my options are :

1 - Panel-Junction box 10 gauge. *Junction box to each heater 12
gauge.
2 - Panel-junction box 12 gauge. *Junction box to each heater 12
gauge.
3 - Panel- junction box 12 gauge. *Junction box to each heater 14
gauge.

None of the above. 1 is completely unnecessary; 2 works fine, but is much more
trouble than it's worth; 3 is a Code violation with either a 20A breaker
(because the 14ga wire is undersized for the breaker) or with a 15A breaker
(because the breaker is undersized for the load).

Instead, run a new 240V circuit, using 14ga wire and a new 15A double-pole
breaker, to supply the new heater, and make sure that the existing circuit
uses a 15A double-pole breaker as well. *Much* less effort than rewiring the
existing circuit.



The final load on the circuit at 240V will be about (if all was on at
full blast) 13.5 amps. *We have never turned on any more than two of
the heaters, but I am pretty sure the proper calculation would require
the worst case scenario.

Yes, it would. This is the worst case: all four heaters drawing maximum
current for more than three hours, which meets the Code's definition of a
"continuous load" and therefore limits the circuit to 80% of its rated
capactiy. Three 750W heaters plus one 1000W heater = 3250W, or just over
13.5A, as you said. Eighty percent of 15A is 12A, so you need a 20A circuit
instead, and that means 12ga wire instead of 14. Don't waste your money on
10ga wire, though. There's no benefit.

If I can add an additional question - just for my personal
knowledge...

At a junction box, why is it bad to step down the gauge of a wire to
match the draw of the load on that wire?
In my case, if I had 12 gauge wire to a junction box, why would 14
gauge from the box to the individual heaters be a violation? If each
is only capable of drawing a few amps, and the "pipe" to the box is
big enough?

Tnx

Doug Miller wrote:
In article , gwandsh wrote:

At a junction box, why is it bad to step down the gauge of a wire to
match the draw of the load on that wire?
In my case, if I had 12 gauge wire to a junction box, why would 14
gauge from the box to the individual heaters be a violation?

Because the Code says so. There are only a few exceptions, and AFAIK this
isn't one of them.

I asked an actual electrician about this once, and he said it was
because the NEXT silly SOB might add yet something else to that leg of
the circuit. (Hey! I can grab power from that box right there! etc...)

--
aem sends...

zxcvbob wrote:
gwandsh wrote:
This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. The other heaters
are 750 watt, wired 240, and draw 2.7 amps each. The circuit is 30
amps, so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.

I was surprised to find the wire to the circuit I planned to pony from
was a 14/2. I traced it back to the junction box, and found each of
the heaters was serviced by a 14 gauge wire. Then I was horrified to
find that the wire from the panel to the main junction box for all
circuits was also a 14 gauge. Even at low amperage, I would expect at
least a 12 gauge, maybe 10?

The existing circuit is fine with 14 ga wire (but it should have a 15A
breaker or fuses, not 30A). You can load it up to 12A, because
resistive heating circuits are limited to 80% of their ampacity -- so
adding a 1000W heater (14 guage wire is good enough) takes you pretty
close to the limit but you're still under.

Make sure that the breakers or fuses are the right size for the wires --
15A. This is important. The rest, not so much.

Bob


I misread your original post. I thought there were two 750W heaters
and you were gonna add a 3rd 1000W heater. If there are three
heaters already, the circuit is maxed out (but safe). Add a new
circuit for the 1000W heater, and 14 gauge wire is plenty.

Bob

Doug Miller wrote:
In article , zxcvbob wrote:
The existing circuit is fine with 14 ga wire (but it should have a
15A breaker or fuses, not 30A).

Right...

You can load it up to 12A, because
resistive heating circuits are limited to 80% of their ampacity --

Right...

so adding a 1000W heater (14 guage wire is good enough) takes you
pretty close to the limit but you're still under.

.. and wrong, and wrong. Do the math. It takes him well *over* the limit, and
14ga wire is *not* "good enough".

3 * 750W existing + 1000W new = 3250W total = 13.5A @ 240V.

He needs 12ga if he's going to put all of them on the same circuit. It's
probably a lot easier to run a new 15A circuit on 14ga wire for the new heater
than it will be to rewire the existing circuit with 12ga.


I misread it. I did do the math, but thought there were 2 heaters.
(I just posted a correction before I read your reply)

Bob

In article , gwandsh wrote:

It occured to me last night that the "paired" circuit breakers I saw
are indeed a 15 amp double poled circuit, rather than a 30 amp as I
reported. It wasn't until this "Eureka" moment that it all made
sense, and I appreciate all the feedback here.

That's a common misunderstanding.

I think I will return the 1000 watt heater (forget to get one with
thermostat anyways, yeesh), and get a 750 watt version. That one I
will pony off one of the existing heater sub-circuits. We have never
turned on more than one heater at a time at this place, and never even
close to max capacity (weekend summer application) so the circuit load
will never be an issue.

Perhaps *you* won't ever turn on all the heaters at once, but what about the
next homeowner? Resistance heating is definitely subject to the 80% rule,
which means that the circuit is limited to 15A * 240V * 80% = 2880 watts. Four
750W heaters is 3000 watts. Not much over the limit, but still over. With all
four in use, the breaker won't trip, but it is possible to overheat the
circuit conductors.


Again, thanks

In article , gwandsh wrote:


At a junction box, why is it bad to step down the gauge of a wire to
match the draw of the load on that wire?
In my case, if I had 12 gauge wire to a junction box, why would 14
gauge from the box to the individual heaters be a violation?

Because the Code says so. There are only a few exceptions, and AFAIK this
isn't one of them.

In article , wrote:
On Sun, 25 Oct 2009 12:13:18 GMT, (Doug Miller)
wrote:

In article ,
wrote:
On Sat, 24 Oct 2009 22:37:59 -0700 (PDT), gwandsh
wrote:

This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. The other heaters
are 750 watt, wired 240, and draw 2.7 amps each. The circuit is 30
amps, so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.
[...]

You are talking about 10.4a or so. (2500w @ 240v = 10.42a)

As I pointed out in another post, his numbers are wrong, but so are yours.
3 * 750W + 1000W = 3250W = 13.5A @ 240V.

You do need to size at the smallest conductor on the circuit.
I would just put a 2 pole 15a breaker on that circuit and get on with
your life being perfectly legal.

This would be good advice if your numbers were right. They're not, and he will

create a hazard if he adds that 1000W heater to the existing circuit.


Hazard?, What hazard? I agree I read two 750w not 3 but the 15a
breaker will still protect the 14 ga wire.
You size the largest load at 125% and the rest at 100%

Code cite on that, please?

I'm specifically questioning the use of the 125% factor for _only a portion_
of a continuous load, as opposed to the _entire_ continuous load.

so he just squeaks in.
1000 x 1.25 = 1250 / 240 = 5.3a
750 x 3 = 2250 / 240 = 9.43a
Calculated load 14.7a

gwandsh wrote:
On Oct 25, 5:09 am, (Doug Miller) wrote:
In article , gwandsh wrote:

This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. The other heaters
are 750 watt, wired 240, and draw 2.7 amps each.
750W / 240V = 3.1A, not 2.7A.

The circuit is 30 amps,
Are you sure? A 15A double-pole breaker is a 15A 240V circuit, not 30A.

so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.
1000W / 240V = 4.2A, not 4.5A.



I was surprised to find the wire to the circuit I planned to pony from
was a 14/2. I traced it back to the junction box, and found each of
the heaters was serviced by a 14 gauge wire. Then I was horrified to
find that the wire from the panel to the main junction box for all
circuits was also a 14 gauge. Even at low amperage, I would expect at
least a 12 gauge, maybe 10?
14-gauge wire is perfectly fine for the existing load: 15A * 240V * 80% =
2880 watts, and you're using only 2250.

Adding another 1000 watts puts you over the limit, though.



So, I have shut off the circuit pending some advice on how to wire it
safely. I expect my options are :
1 - Panel-Junction box 10 gauge. Junction box to each heater 12
gauge.
2 - Panel-junction box 12 gauge. Junction box to each heater 12
gauge.
3 - Panel- junction box 12 gauge. Junction box to each heater 14
gauge.
None of the above. 1 is completely unnecessary; 2 works fine, but is much more
trouble than it's worth; 3 is a Code violation with either a 20A breaker
(because the 14ga wire is undersized for the breaker) or with a 15A breaker
(because the breaker is undersized for the load).

Instead, run a new 240V circuit, using 14ga wire and a new 15A double-pole
breaker, to supply the new heater, and make sure that the existing circuit
uses a 15A double-pole breaker as well. *Much* less effort than rewiring the
existing circuit.



The final load on the circuit at 240V will be about (if all was on at
full blast) 13.5 amps. We have never turned on any more than two of
the heaters, but I am pretty sure the proper calculation would require
the worst case scenario.
Yes, it would. This is the worst case: all four heaters drawing maximum
current for more than three hours, which meets the Code's definition of a
"continuous load" and therefore limits the circuit to 80% of its rated
capactiy. Three 750W heaters plus one 1000W heater = 3250W, or just over
13.5A, as you said. Eighty percent of 15A is 12A, so you need a 20A circuit
instead, and that means 12ga wire instead of 14. Don't waste your money on
10ga wire, though. There's no benefit.

If I can add an additional question - just for my personal
knowledge...

At a junction box, why is it bad to step down the gauge of a wire to
match the draw of the load on that wire?
In my case, if I had 12 gauge wire to a junction box, why would 14
gauge from the box to the individual heaters be a violation? If each
is only capable of drawing a few amps, and the "pipe" to the box is
big enough?

Tnx


There is nothing wrong with that, but (with a few exceptions*) the
breaker has to protect the smallest sized wire. So with a long run
of 12 gauge wire (to reduce voltage drop) that then taps off with a
14 gauge wire, you need a 15A breaker.

*there are some exceptions, like the "10 foot tap rule" which might
be used for a kitchen with a split cooktop and oven on the same 40A
circuit.

Bob

On Oct 25, 11:27*am, (Doug Miller) wrote:
In article ,gwands wrote:



It occured to me last night that the "paired" circuit breakers I saw
are indeed a 15 amp double poled circuit, rather than a 30 amp as I
reported. *It wasn't until this "Eureka" moment that it all made
sense, and I appreciate all the feedback here.

That's a common misunderstanding.



I think I will return the 1000 watt heater (forget to get one with
thermostat anyways, yeesh), and get a 750 watt version. *That one I
will pony off one of the existing heater sub-circuits. *We have never
turned on more than one heater at a time at this place, and never even
close to max capacity (weekend summer application) so the circuit load
will never be an issue.

Perhaps *you* won't ever turn on all the heaters at once, but what about the
next homeowner? Resistance heating is definitely subject to the 80% rule,
which means that the circuit is limited to 15A * 240V * 80% = 2880 watts. Four
750W heaters is 3000 watts. Not much over the limit, but still over. With all
four in use, the breaker won't trip, but it is possible to overheat the
circuit conductors.





Again, thanks- Hide quoted text -

- Show quoted text -

I hear your concerns. While I plan to own this place for many years,
I am a big proponent of doing things right and not handing my problems
off to someone else. I certainly could not handle it if any harm came
to someone downstream from my actions.

I will add a new circuit and string a new 14 gauge wire for the new
heater.

Again my thanks to the group knowledge base.

In article , wrote:
On Sun, 25 Oct 2009 18:32:00 GMT, (Doug Miller)
wrote:

Hazard?, What hazard? I agree I read two 750w not 3 but the 15a
breaker will still protect the 14 ga wire.
You size the largest load at 125% and the rest at 100%

Code cite on that, please?

I'm specifically questioning the use of the 125% factor for _only a portion_
of a continuous load, as opposed to the _entire_ continuous load.



You are right, I should not have said 125% of the largest load, it is
125% of all of them (16,92a) BUT 240.4(D) applies to the breaker
allowed, not the circuit ampacity, since the 80% rule is already built
into that number.
The ampacity of 14ga wire is 20a, the maximum O/C device is 15a unless
otherwise allowed.(not here)

Look at 210.19 FPN No. 1: "See 310.15 for ampacity ratings of
conductors."

And you're right about that -- I'd forgotten that the 80% rule was already
built in to the overcurrent ratings for 14- and 12-gauge conductors.

BTW these are the kinds of questions that will divide a room full of
inspectors.
The bottom line is a 15a breaker will adequately protect 14ga wire, no
matter what you do with it and those heaters should not trip a 15..

Agreed.

"gwandsh" wrote in message
...
This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. The other heaters
are 750 watt, wired 240, and draw 2.7 amps each. The circuit is 30
amps, so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.

I was surprised to find the wire to the circuit I planned to pony from
was a 14/2. I traced it back to the junction box, and found each of
the heaters was serviced by a 14 gauge wire. Then I was horrified to
find that the wire from the panel to the main junction box for all
circuits was also a 14 gauge. Even at low amperage, I would expect at
least a 12 gauge, maybe 10?

So, I have shut off the circuit pending some advice on how to wire it
safely. I expect my options are :

1 - Panel-Junction box 10 gauge. Junction box to each heater 12
gauge.
2 - Panel-junction box 12 gauge. Junction box to each heater 12
gauge.
3 - Panel- junction box 12 gauge. Junction box to each heater 14
gauge.

The final load on the circuit at 240V will be about (if all was on at
full blast) 13.5 amps. We have never turned on any more than two of
the heaters, but I am pretty sure the proper calculation would require
the worst case scenario.

Can anybody tell me what the best wiring combination is? I will ask
my electrician to do the final connection of the panel to the junction
box, but I would like to have the wiring from the junction box to the
heaters in place to save some bucks.

tnx in advance


A 15 amp load is OK on a 14 gage wire. If you were running the same heaters
on 120v you would be in trouble.

On Wed, 28 Oct 2009 04:48:58 -0800, "Roger Shoaf"
wrote:

[snip]

The final load on the circuit at 240V will be about (if all was on at
full blast) 13.5 amps. We have never turned on any more than two of
the heaters, but I am pretty sure the proper calculation would require
the worst case scenario.

Can anybody tell me what the best wiring combination is? I will ask
my electrician to do the final connection of the panel to the junction
box, but I would like to have the wiring from the junction box to the
heaters in place to save some bucks.

tnx in advance


A 15 amp load is OK on a 14 gage wire. If you were running the same heaters
on 120v you would be in trouble.


Those heaters which draw 13.5A at 240V (3240W) will draw 6.75A at 120V
(810W). The trouble isn't electrical.

On Oct 26, 8:23*pm, (Doug Miller) wrote:
In article , wrote:
On Sun, 25 Oct 2009 18:32:00 GMT, (Doug Miller)
wrote:

Hazard?, What hazard? I agree I read two 750w not 3 but the 15a
breaker will still protect the 14 ga wire.
You size the largest load at 125% and the rest at 100%

Code cite on that, please?

I'm specifically questioning the use of the 125% factor for _only a portion_
of a continuous load, as opposed to the _entire_ continuous load.

You are right, I should not have said 125% of the largest load, it is
125% of all of them (16,92a) BUT 240.4(D) applies to the breaker
allowed, not the circuit ampacity, since the 80% rule is already built
into that number.
The ampacity of 14ga wire is 20a, the maximum O/C device is 15a unless
otherwise allowed.(not here)

Look at 210.19 FPN No. 1: "See 310.15 for ampacity ratings of
conductors."

And you're right about that -- I'd forgotten that the 80% rule was already
built in to the overcurrent ratings for 14- and 12-gauge conductors.



BTW these are the kinds of questions that will divide a room full of
inspectors.
The bottom line is a 15a breaker will adequately protect 14ga wire, no
matter what you do with it and those heaters should not trip a 15..

Agreed.- Hide quoted text -

- Show quoted text -

Exactly:
Suggestion; Change the double pole breaker to 15 amp, 15 x 240 =3600
watts and that size breaker protects the 14AWG wiring. Retain existing
14AWG wiring, use 14AWG for the new 100 watt heater.
The existing three 750 watt heaters draw 3 x 750 = 2250; add 1000 for
the new heater 2250 + 1000 = 3250.
That 3250/240 = 13.54 amps. That's within the 15 amp rating of the
whole circuit.

On Oct 28, 4:48*am, "Roger Shoaf" wrote:
"gwandsh" wrote in message

...





This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. *The other heaters
are 750 watt, wired 240, and draw 2.7 amps each. *The circuit is 30
amps, so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.

I was surprised to find the wire to the circuit I planned to pony from
was a 14/2. *I traced it back to the junction box, and found each of
the heaters was serviced by a 14 gauge wire. *Then I was horrified to
find that the wire from the panel to the main junction box for all
circuits was also a 14 gauge. *Even at low amperage, I would expect at
least a 12 gauge, maybe 10?

So, I have shut off the circuit pending some advice on how to wire it
safely. *I expect my options are :

1 - Panel-Junction box 10 gauge. *Junction box to each heater 12
gauge.
2 - Panel-junction box 12 gauge. *Junction box to each heater 12
gauge.
3 - Panel- junction box 12 gauge. *Junction box to each heater 14
gauge.

The final load on the circuit at 240V will be about (if all was on at
full blast) 13.5 amps. *We have never turned on any more than two of
the heaters, but I am pretty sure the proper calculation would require
the worst case scenario.

Can anybody tell me what the best wiring combination is? *I will ask
my electrician to do the final connection of the panel to the junction
box, but I would like to have the wiring from the junction box to the
heaters in place to save some bucks.

tnx in advance

A 15 amp load is OK on a 14 gage wire. *If you were running the same heaters
on 120v you would be in trouble.- Hide quoted text -

- Show quoted text -

Thought I would finish the story here. We decided to keep the 1000
watt/ 240V heater unit since there would be no load issues with the
new circuit.

I ran a new circuit with 14/2 Romex to the heater location, leaving
six feet of wire hanging beside the panel. I bought and wired the
(internal) thermostat for the heater according to the supplied
diagram, and bought the compatible 2 pole 15 amp circuit breaker.

My electrician friend visited - he verified my thermostat wiring,
checked the wire routing, wired and installed the new circuit breaker
all in about 10 minutes. Works like a champ.

The whole thing took a while to figure out, but little time to
implement. We now have warm floors when needed in the kitchen. Tnx
to everybody who helped out.