5000w electric heater wiring?

[cadunkle]

I got a Comfort Zone 5000w electric heater for my shed. I am somewhat unsure of the wiring required. The manual says use at least 10ga wire, but also says to use a 32-40 amp breaker. I wired it up on a 30 amp breaker and 10/2 Romex for now, and measured the amps using a clamp on ammeter. This heater has a switch to run at 3k/4k/5k watts. At the heater I measure 13.4/17.8/22.1 amps. At the breaker I see 22.5 amps on the 5k watt setting.

My understanding is for a continuous load such as electric heat you derate the wire and breaker at 125% of load, which would mean a 30 amp breaker is good for a 24 amp continuous resistive load. Is 10ga wire okay to use with this heater?

Walls in the shed are unfinished but I'm closing in the ceiling and insulating, and may do the walls eventually. I have a short run of Romex direct to the heater but I have a metal box and faceplate with knockout I want to terminate the Romex in this box and install MC cable from the box to the heater. Before I get material for this I want to be sure 10ga wire is sufficient. Given the load is under 24 amps and I ran it for a few hours today at 5k watts while working in the shed and the 10ga wire does not feel hot or warm. Thoughts?

 

[nadogail]

Heaters are classified as Continuous Loads, and require the heavier wire.

 

[cadunkle]

Heavier than 10ga for a 22.5 amp continuous load? What size wire?

I do have a fair amount of 6/3 Romex left over from another project along with a bunch of 6ga THHN. The panel in the shed is fed with 6ga THHN. Doesn't hurt to go overkill to be safe. I had considered running the 6/3 I already have in the wall to a box, then 8/2 MC to the heater. I'd have to get a 35 amp or larger breaker to have lugs for the 6/3.

 

[VT JD]

Not sure where you live but in most jurisdictions 10/2 on a 30 amp 2 pole breaker is all you need for a 5kw electric heater.

 

[u2slow]

#10 is usually 30A rated and can be loaded continuously to 24A (80%). 30A breaker is normal.

If this product is manufactured outside north america, 32A overcurrent may be a more common size in those locales.

 

[Lou's Garage]

I have two similar heaters that I've run for years on 10 ga. wire / 30A breakers without any problems.

Lou Manglass

 

[cannuck]

You are IMHO right on the edge with 10 ga. - depending on how the wire is routed and cooled and how long it is - and what temp the insulation is rated for. I an NOT a sparky, but work with a mess of EEs, CEETs and electricians, and notice that they will spend the money and go up one size on anything they do for themselves. That speaks volumes to me.

 

[u2slow]

With a heater.... if the run is long and/or voltage sags.... the current draw becomes less and the heat output goes down. Basic ohm's law.

Motors, especially, are where you want to step up the wire when you're on the borderline.

 

[cannuck]

With a heater.... if the run is long and/or voltage sags.... the current draw becomes less and the heat output goes down. Basic ohm's law.

Motors, especially, are where you want to step up the wire when you're on the borderline.

Of course, exactly true, but for my purposes I will plug a lot of things into the same receptacle over time, so a heater plug might well become a motor plug - and we don't suffer too much voltage lag here. But: to your point: I just finished a $15k dry air supply for a client that runs 250V single phase (as we can get that on most job sites or from a little genset) and they could NOT run it at all in a major industrial plant. The machine was rated at 200-250 V but the leg of a 208 circuit they were tapping turned out to have only 188V available and the resulting amperage draw (motor loads) exceeded what the protection would allow to pull in.

Yours are words from the wise.