Any Advantage?

Stephen

Want to put in a wall mounted htr. is there any real difference or advantage between a 1000w. 120v. and a 1000w. 240v. efficiency?
Thanks Stephen

Speedy Petey

Not enough that you'd EVER see the benefit of.
For something that small it's not even worth it for the wire size benefit.

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Celtic

What wire size benefit?

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mdshunk

The one realized if you were debating the use of a 5000 watt heater at either 120 or 240. In the case of this small one, you're basicly talking about the same wire gauge. As you get larger, the gauge disparity becomes more evident between operating voltages.

Speedy Petey

Yup. That one.

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Sparky Joe

At any rate, since it's the same size wire for both voltages, at 240V you are 4 times as efficient due to IsquareR losses, only sacrifice is one more space in your panel

EDIT;
Given - 2.05 ohms/Kft #12 stranded (table 8 chapter 9)

At 240 volts you lose 35.6 Watts on the wire alone (heater uses 1035.6 watts)
At 120 volts you lose 142.25 Watts on the wire (heater uses 1142.25 watts)

This is ohms/Kft but that is actually only a 500 foot run

Celtic

Which one would that be?

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mdshunk

Are you kidding me? Watts are watts. THe kilowatt consumption will be identical.

Sparky Joe

Sorry I was slow with my math, but not only the heating element uses power.
Anything with resistance and current consumes power.
Or do people just enjoy working with 277 over 120?

mdshunk

It's to keep the wire gauges down and the voltage drop to a minimum. Resistive loads will consume the same amount of power without regard to the operating voltage. The determining factor is the installed cost when wire gauge is considered.

Sparky Joe

"line losses" is what I was referring to;
This wattage formula is printed directly on the front of every Ugly's book.

12 gauge stranded wire = 2.05ohms per 1000feet (table 8 chapter 9 NEC)
1000watts at 120volts = 8.33amps
1000watts at 240volts = 4.167amps

120 Volts;
8.33squared x 2.05 = 142.25watts


240 Volts;
4.167squared x 2.05 = 35.6watts

(notice it's not twice as efficient when you double the voltage, but 4 times)

The constant used (2.05) is per 1000 feet of #12 wire, but this circuit consists of 2 wires(at 120 or 240), so the actual distance would be half, or 500 feet. If the original poster had a distance I could give him exact numbers.

mdshunk

Yes, you're talking about line losses, which don't really apply in a resi setting. We're talking about a home run that might be 50 feet at a normal maximum. You can pretty much discount line losses (voltage drop) in a residential setting. He's sure not going to have a 1000 feet of cable between hither and tither.

Sparky Joe

If voltage drop is the concern;

2KIL/Cmil (we'll use 500' for the length)

120 Volts;
2 x 12.9 x 8.33 x 500 / 6530 = 16.46 Volts
delivering 103.5 Volts and putting out 744 Watts of heat


240 Volts
2 x 12.9 x 4.167 x 500 / 6530 = 8.23 Volts
delivering 231.8 Volts and putting out 932 Watts

The difference is easy to see, given that this is at 500 feet which is probably twice around the guys house, but for use every winter for 20 years, the distance may as well be 10,000 feet.

mdshunk

I'm going to have to ask everyone to forgive Joe. He's aparently got an uncontrollable urge to do math with large numbers.

Sparky Joe

I apologize, it seems you're right, I just thought the question was about efficiency?

And according to the math at 50ft, he would save 75cents per year with 240(of course all numbers are assumed)

Celtic

How long would it take to recoup the difference in price between the single pole 15A CB and 120v heater vs. the two pole 15A CB and the 240v heater?

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jproffer

And the difference in price between 14/2 and 14/3 for X feet (NOT 500, Joe)

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Jim P.

Sparky Joe

why would he pull 14/3?

jproffer

I had in my head, for whatever reason, that he had 110 controls, which is not correct. You're right Joe...but don't let it go to your head.

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Jim P.

mdshunk

In fairness, sometimes the price of the heater dictates which one gets used. If a 240 volt heater is a stock item, and the 120 volt version is special order, the 240 volt one will likely get used. Vice-versa also. This is really only an issue with the real small heaters. Bigger stuff is gonna be 240 normally, whether you like it or not.