Need help with wiring questions

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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
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wrote:

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.
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snipped-for-privacy@aol.com wrote:

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...
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aemeijers wrote:

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).
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HeyBub wrote:

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....
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His IP address indicates Portland, Oregon.

There's nothing one bit unusual about running a 15A 240V circuit on 14-2. Why do you think there is?
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As I pointed out in another post, his numbers are wrong, but so are yours. 3 * 750W + 1000W = 3250W = 13.5A @ 240V.

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.
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On Sun, 25 Oct 2009 12:13:18 GMT, snipped-for-privacy@milmac.com (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% so he just squeaks in. 1000 x 1.25 = 1250 / 240 = 5.3a 750 x 3 = 2250 / 240 = 9.43a Calculated load 14.7a
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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.

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On Sun, 25 Oct 2009 18:32:00 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

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."
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..
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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.

Agreed.
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On Mon, 26 Oct 2009 23:23:56 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

No problem partner. As I say, those kind of questions will usually start an argument at an IAEI meeting. The real thing to remember is you have to use 240.4(D) to size wire when you have receptacles and lampholders, where the installer has no control over what the user plugs in. That is pretty much what 210.23 is all about
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On Oct 26, 8:23pm, snipped-for-privacy@milmac.com (Doug Miller) wrote:

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.
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gwandsh wrote:

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
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wrote:

Right...
Right...
.. 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.
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Doug Miller wrote:

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
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zxcvbob wrote:

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
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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

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

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

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

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.

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.

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.
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On Oct 25, 5:09am, snipped-for-privacy@milmac.com (Doug Miller) wrote:

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
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