Need help with wiring questions

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.

Reply to
Doug Miller
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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

Reply to
zxcvbob

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.

Reply to
gwandsh

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..

Reply to
gfretwell

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.

Reply to
Doug Miller

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

Reply to
gfretwell

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.

Reply to
Roger Shoaf

If he ran "the same heaters" on 120v he wouldn't be in trouble but he might be cold. A 1000w 240v heater is a 250w heater at 120v.

Reply to
gfretwell
[snip]

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

Reply to
Gary H

Exactly: Suggestion; Change the double pole breaker to 15 amp, 15 x 240 =3D3600 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 =3D 2250; add 1000 for the new heater 2250 + 1000 =3D 3250. That 3250/240 =3D 13.54 amps. That's within the 15 amp rating of the whole circuit.
Reply to
terry

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.

Reply to
gwandsh

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