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Old 09-25-2010, 02:02 AM   #1
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Default 240 VAC heating elements and 110 VAC

OK, can someone settle this for me. I have heard two stories about using a 240 VAC heating element with 110 VAC. Common sense says halving the power should give you half the wattage out of the heating element. However, I have also been told that it is not linear. If it isn't linear, is there a formula to figure out how many watts you will end up with - for instance: if I want 1800 watts with 110 VAC out of the heating element, could I use a 3500 Watt 240 VAC; or, would I need to use say a 4500 watt 240 VAC element?

Hope that made sense.

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Old 09-25-2010, 02:21 AM   #2
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Power = the square of the voltage applied divided by the resistance of the element. The resistance of the element can be determined by dividing the square of the rated voltage by the power rating. The net result is that at 120 volts (1/2 the voltage) a 240 volt element will only put out 1/4 of the power.
To get 1800 watts at 120 VAC you would need a 7200 watt, 240V element, if they even make one like that, which I doubt.

Taking the 3500 watt, 240V element as an example, the element resistance is (240*240)/3500 = 16.46 ohms. With 120 volts applied, the power is (120*120)/16.46 = 875 watts, or 1/4 the rated value.

A 4500 watt element would only develop 1125 watts at 120 V.

EDIT: Forgot to mention - if you want 1800 watts at 120V, why not just use a 2000 watt element that is rated for 120 volts? You would need a 20 amp circuit for that, but you could use a 1500 watt, 120V element on a standard 15 amp circuit.

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Old 09-25-2010, 12:58 PM   #3
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EDIT: Forgot to mention - if you want 1800 watts at 120V, why not just use a 2000 watt element that is rated for 120 volts? You would need a 20 amp circuit for that, but you could use a 1500 watt, 120V element on a standard 15 amp circuit.
Well, I only have 15 amp breakers in my apartment right now. After I get married in April I will have 240 out of her dryer outlets at her apartment...I think they're GFCI...
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Old 10-04-2010, 08:15 PM   #4
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Originally Posted by DeafSmith View Post
Power = the square of the voltage applied divided by the resistance of the element. The resistance of the element can be determined by dividing the square of the rated voltage by the power rating. The net result is that at 120 volts (1/2 the voltage) a 240 volt element will only put out 1/4 of the power.
To get 1800 watts at 120 VAC you would need a 7200 watt, 240V element, if they even make one like that, which I doubt.

Taking the 3500 watt, 240V element as an example, the element resistance is (240*240)/3500 = 16.46 ohms. With 120 volts applied, the power is (120*120)/16.46 = 875 watts, or 1/4 the rated value.

A 4500 watt element would only develop 1125 watts at 120 V.

EDIT: Forgot to mention - if you want 1800 watts at 120V, why not just use a 2000 watt element that is rated for 120 volts? You would need a 20 amp circuit for that, but you could use a 1500 watt, 120V element on a standard 15 amp circuit.
So, I think I WILL end up wiring it for 240 vac. How do I make it GFCI?
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Old 10-04-2010, 08:26 PM   #5
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A lot of people put a spa disconnect panel in line - you can get one of these with a 50 amp 240V GFCI breaker in a metal box for about $50 from Home Depot. You will need to use at least 10 gauge wire, and depending on the length of the power cable you need, it may well end up costing more than the spa panel. And then there are the 240V plugs and receptacles to buy. So count on spending at least $150 or more.

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Old 10-04-2010, 08:37 PM   #6
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Thanks Deafsmith.

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Old 10-17-2010, 01:45 AM   #7
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A lot of people put a spa disconnect panel in line - you can get one of these with a 50 amp 240V GFCI breaker in a metal box for about $50 from Home Depot. You will need to use at least 10 gauge wire, and depending on the length of the power cable you need, it may well end up costing more than the spa panel. And then there are the 240V plugs and receptacles to buy. So count on spending at least $150 or more.
This is all I could find...I don't think it's right since it's three times what you estimated. http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053
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Old 10-17-2010, 02:10 AM   #8
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This is all I could find...I don't think it's right since it's three times what you estimated. http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053
I think he was talking about something like this:
http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053
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Old 10-17-2010, 04:50 AM   #9
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Yes, that last one for $49 is the one.
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