romex wire and breaker to use

solutions · Mar 30, 2008

I would like to install a motion light. It is 750 watts total (each of the three lights 250 watts) In the place i want to install the fixture, has existing 14/2 that goes to a 15 amp breaker. At the big box store they tell me 14/2 will work ok with a 15 amp breaker( very leary of there advice in general) but is 14/2 the safest and best to run this type lighting and wattage?

Thank you all!!

Jimbo · Mar 30, 2008

750 watts is about 6 amps. The general rule in residential wiring is that a 15 amp breaker can be wired to 14 guage wire, and should have a continuous load not exceeding 12 amps. ( Short term uses like a toaster, or hair dryers, are not condsidered contiuous. A light fixture is.)
If there are no other loads on the circuit ,you are fine. If there are other loads, then you would have to evaluate the whole picture.

Sponsor · 2022-01-29T12:20:58-0800

solutions · Mar 30, 2008

Thanks for the reply Jimbo..Sounds great! Yep, the motion sensor light will be the only thing on the circuit.

JWelectric · Mar 30, 2008

jimbo said:
750 watts is about 6 amps. The general rule in residential wiring is that a 15 amp breaker can be wired to 14 guage wire, and should have a continuous load not exceeding 12 amps. ( Short term uses like a toaster, or hair dryers, are not condsidered contiuous. A light fixture is.)
If there are no other loads on the circuit ,you are fine. If there are other loads, then you would have to evaluate the whole picture.

Jimbo-
There is no such thing as a continuous load in residential wiring even if it is left on 24 hours a day 7 days a week.

Jimbo · Mar 30, 2008

Well, what do you expect on a plumber's forum!!! But what is this 80% rule we hear about? How many ampls can you put on a 15 amp circuit?

Speedy Petey · Mar 30, 2008

If you consider this a "Plumber's forum", then why bother having topics like "Electrical Forum discussions"?

Speedy Petey · Mar 30, 2008

This is one of the few times I have to disagree with Mike.

Things like some lighting and electric heaters are considered continuous loads, by direct statements or by definition.

JWelectric · Mar 30, 2008

Speedy Petey said:
This is one of the few times I have to disagree with Mike.

Things like some lighting and electric heaters are considered continuous loads, by direct statements or by definition.

Itâ€™s perfectly okay to disagree with me and sometimes I learn from the debate.

When you say that electric heaters are considered continuous loads by direct statement you would be correct as outlined in section 424.3(B) Branch-Circuit Sizing. Fixed electric space heating equipment shall be considered continuous load and even 422.13 for water heaters.

But for lighting the load is simply three watts pre square foot and it is not considered a continuous load in residential applications. In other words an 1800 watt lighting load on a 15 amp circuit in a residential circuit is 1800 watts for three minutes or for three days.
There is no requirement of do the three hours or more is continuous for residential lighting circuits. For the general purpose and small appliance circuits there is no minimum or maximum number that is allowed. The only limit is outlined in 220.14(J).

It would be a good design to limit the number of lighting outlets on one circuit but it is not a code requirement.

Chris75 · Mar 30, 2008

I agree with JW, Continuous loads in residential are far and few...

Speedy Petey · Mar 30, 2008

To be honest I never thought of it that way, meaning that it is included in the demand load like that, even for additional circuits.

I get what you mean now.

Jimbo · Mar 31, 2008

Speedy Petey said:
If you consider this a "Plumber's forum", then why bother having topics like "Electrical Forum discussions"?

I generally consider there to be two categories of questions here....DIY questions which can be answered by plumbers with DIY-type general knowledge, and more technical questions. I stay away from the second type for sure, but sometimes try to help on the first category.

Anyway, just for my own knowledge....could you install an 1800 watt baseboard heater on a 15 amp circuit, with 12 guage? May or may not be a good idea....but would it comply with code?

Speedy Petey · Mar 31, 2008

jimbo said:
Anyway, just for my own knowledge....could you install an 1800 watt baseboard heater on a 15 amp circuit, with 12 guage? May or may not be a good idea....but would it comply with code?

No. Electric heat is considered a continuous load.

210.20 Overcurrent Protection
Branch-circuit conductors and equipment shall be protected by overcurrent protective devices that have a rating or setting that complies with 210.20(A) through (D).

(A) Continuous and Noncontinuous Loads Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.

But the question begs: If using #12 WHY bother with a 15A breaker in the first place?

Mikept · Mar 31, 2008

Old #12Al...

KD · Apr 2, 2008

When talking about wire, we assume it is Copper. If you are using Aluminum please tell us.

Jimbo · Apr 2, 2008

Speedy Petey said:
No. Electric heat is considered a continuous load.

Well, that was the point of my question, because JW had posted this :
"Jimbo-
There is no such thing as a continuous load in residential wiring even if it is left on 24 hours a day 7 days a week."

Now, I'm confused!

Speedy Petey · Apr 2, 2008

Re-read post #8.

JWelectric · Apr 2, 2008

jimbo said:
Well, that was the point of my question, because JW had posted this :
"Jimbo-
There is no such thing as a continuous load in residential wiring even if it is left on 24 hours a day 7 days a week."

Now, I'm confused!

Don't be confused as I may have spoke a little premature in my first post. When doing the branch circuit supplying any resistive load then the 125% rule comes into play but when doing a service calculation the 125% does not come into play on residetial loads.

Jimbo · Apr 2, 2008

Thanks very much. I'm going back to clogged toilets!!

romex wire and breaker to use

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