Roof heat tape & watts question

Community Playground General Discussions
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Hi.

I am always confused about electrical terms, and have a question about the difference between "600 watt (incandescent) " and “1800 watt (resistive)”. I am having some runs of danfoss heat tape installed to prevent ice dams. The longest run is listed at 760w and 6.3 amps. I would like to use several of the ge/jasco 45604 outdoor modules to activate them. The specs on the ge switches claim either 600w or 1800w, 15 amps.

So my question is, which of the wattage numbers do I follow? The 600 or the 1800?

Thanks a lot for your help.

Edit: also found a Wayne Dalton outdoor module that is similar to the ge but lists no watt load limits but either 15a or 8.3a tungsten, which if my math is correct would be about 1000 watts (120v x8.3a) Am I interpreting all of this correctly?

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[quote=“jaccord, post:1, topic:168638”]The specs on the ge switches claim either 600w or 1800w, 15 amps.

So my question is, which of the wattage numbers do I follow? The 600 or the 1800?[/quote]

I found a page here that explains it better than I could: About relay contact current ratings

Take a multimeter to the heat tape and measure the resistance of the entire length, cold. Then plug it in and let it warm up, then disconnect it and measure the resistance again. You should get similar number—maybe 20 Ω—both times. If so, the 1800 W on the switch is the important one, because you’ve got a load (the tape) whose resistance doesn’t change much with its temperature. If that’s the case, you can safely drive two 760-watt lengths from one switch.

also found a Wayne Dalton outdoor module that is similar to the ge but lists no watt load limits but either 15a or 8.3a tungsten, which if my math is correct would be about 1000 watts (120v x8.3a) Am I interpreting all of this correctly?

I think so, yes.

(Disclaimer: I am not an electrician, but I have studied electrical engineering and I know Ohm’s law. This matters a lot less at 240 V where I live, because the same power incandescent lamp has four times the resistance here than in 120-volt land.)

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Or if you don’t want to deal with a multimeter… search amazon for “watt meter”. You can plug
anything (within reason) into it and it will tell you exactly what you are drawing. Great for many
other things around the house as well.

Good Luck
Les

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Les - I am in Colorado using a Vera Edge controller and trying to figure out the best interface b/w my electrical panel and 220v <100ft run of tape. I am looking at the Elk-9200 relay/contacts coupled with the Evlove 110 z-wave receptacle. Heavy Duty Relay/Contactor - ELK Products

Any other suggestions?