Need help with wiring questions

[gwandsh]

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

[gfretwell]

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.

[zxcvbob]

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

[aemeijers]

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...

[HeyBub]

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).

[RBM]

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

>

[aemeijers]

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....

[Doug Miller]

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.

[Doug Miller]

[...]

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.

[Doug Miller]

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?

[Doug Miller]

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.

[cshenk]

"gwandsh" wrote

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).

[gfretwell]

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

[gwandsh]

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

[gwandsh]

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

[aemeijers]

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]

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

[zxcvbob]

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

[Doug Miller]

That's a common misunderstanding.

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.

[Doug Miller]

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