14 vs. 12 gauge wire**

Hi. I'm adding an 120 volt, 12.5 amp, 1500 watt electric heater to my sunroom. I gave it a dedicated 15 amp circuit and ran it with 12 gauge wire. Is that correct for the amout of power required by the heater?

 

It is fine for the 15 amp circuit...in fact its more than fine...15 amp require 14 gauge minimum, 20 amp requires 12 gauge minimum.

 

Because you are drawing a lot of current, the distance from the breaker to the appliance becomes an issue due to voltage drop. A 12 gauge wire should be good for about 100 feet. If the run is longer than that, use a 10 gauge wire.

 

I actually said 12 when i meant i did it with 14 gauge. it's abot 120 feet. sounds like i'll need to use 12 gauge. Or, if i get a 8 amp heater i won't have to rewire (it was a total pain in the butt getting it there).

 

Actually the wire should be sized according to the breaker so assuming a 15 amp breaker size the wire accordingly. As said earlier you may need to account for voltage drop.

 

Voltage drop is not a significant issue in this particular case. _Normally_ you want to limit voltage drop to less than 5%, but this is not a hard and fast requirement; it is simply good design practise to prevent lights from dimming make it easy for motors to start. You won't have either of these problems with an electric heater; instead it will simply put out a bit less heat, and the thermostat will keep it on for longer periods of time.

You have a separate problem: the '80% rule'. You are not permitted to supply a _continuous _ load that uses more than 80% of the breaker capacity. This means that if you run 14 ga wire with a 15A breaker, the maximum continuous load that you may place on this circuit is 12A.

Heaters are often not considered continuous loads, because the thermostat will cause it to turn on and off, but if the heater is undersized for the room, and will be running continuously, then this heater is too large for this circuit.

-Jon

 

thank you all very much! I think I will be in good shape. The heater is more than the room needs and there are also other radiators nearby providing heat so it will not be on continuously.

 

Winnie's advice is good. This heater since it is fixed in place most likely must be considered a continous load. Even though heaters are among the most efficient appliances, good design overcomes unforeseen problems for the DIYer. Your voltage drop at 120 feet using 14 awg and a 12.5 amp load assuming you start with 120 volts at the panel and 40 C as the ambient is going to be 8.2 volts or 6.8% (111.8 volts). Not acceptable in my opinion. But Winnie points out this is too large of a load for 14 awg serving a _continious load_. So is irrelevant. Using 12 awg and the same parameters you have 114.9 volts and 4.1% drop. Personnally I would consider only 240 volt heaters at that distance.
To size the wire you consider the load (amperage it must carry). The breaker is sized by the amperage rating of the device it protects. Then adjustments can be considered for the wire size due to voltage drop.

 

Fixed in place does not imply a continuous load. However, there is a separate 80% rule for fixed-in-place appliances (independent of the continuous load rule), so the effect is similar.

I agree with Jon that the level of acceptable voltage drop is not a constant. It depends on the type of load. For resistive loads, voltage drop is considerably less important. But if this unit has a fan, excessive voltage drop will shorten its life. If you hadn't run any wire yet, I'd certainly advise doing better than #14. But since you've already run it, and since you said it was a "total pain in the butt", I'm not sure I'd advise replacing it.

 

Sorry, "fixed in place" does not dictate continious load but it does mean _continuous_ to some of us

 

In a residence there are very few things that can be considered a continuous load, heaters included. A continuous load is something "expected" to be on for 3 hours or more. A general use heater does not fall into this category IMO.

In any case I agree that the 14 is too small. Wouldn't a simpler solution be to just get a 240 volt heater as suggested? This will solve the whole issue. 240 volt loads are much less succeptable to voltage drop, and the amperage will be roughly half that of the 120 volt heater for the same wattage.

 

Yes I agree Speedy and I was in error to suggest that a "fixed in place" heater is a continuous load. Heres my problem with these wall heaters and space heating in general in residences. People dont size them right for the room they want to heat, nor do many let the thermostat do its job. They just want to be warm in room that doesnt seem to be kept warm, as they would like, by the primary heating system. I dont know how many homes I've been in where these heaters rarely cycle. As mentioned earlier in this thread, if you cant deliver the correct voltage, the heater wont get as warm as specified. A recipe in my opinion to run a heater _continiously_ to try to keep up with the heat loss of that room. Baseboard heat is another subject.....Anyway IMO the NEC needs to rethink these type heaters in homes as to continious load.

 

It doesn't really matter. There are already at least two other articles in the NEC which require you to size the circuit the same as if they were a continuous load anyway. So designating them a continuous load would impose no additional restrictions.

 

I suppose John that articles in 210 and 424 do make this the case and would be rather redundant. So I will concede that it probably gains no benefit to flatly state fixed space heating is continious. I still think at 120 volts and 14 awg at 120 feet is poor design for this heater. I do have a question though....space heaters of the the resistive type (cord and plug type) are required to operate on 110 volts though rated at 120 volts is this also true of fixed wall heaters with or without motors?