5000W Water Heater

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Chris is there any chance the heaters are 5000 watts at 240 and 3750 at 208? Not that i'll matter much because of the fraction of the amp.
 
RUWired said:
Chris is there any chance the heaters are 5000 watts at 240 and 3750 at 208? Not that i'll matter much because of the fraction of the amp.
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Was going to say the same thing. Most residential water heater, HVAC heat strips, and electric ranges are advertised at their 240V wattage. If you run them at 208V, you'll draw less amps and have a lower watt rating. The nameplates usually have values for both voltages.
 
A water heater is a fixed resistance load. You're changing the applied voltage across a fixed resistance, so the current must be different in each case. You can not have a fixed wattage resistive device when the applied voltage changes.

For 5000w @ 240, the amps are 20.83. This implies a resistance of 11.52 ohms.

Put 208V across 11.52 ohms, and the current will be 18.06 amps. At 208V, 18.06 amps is 3756 watts.

If this element was designed only for 208V, then it will have a smaller resistance and allow enough current to flow to make 5000W. But if you connected it to 240V, it would draw more amps and more power.

Motors are different, because they are load driven and their resistance changes based on load and applied voltage. They will suck more amps to make the power they need to make. Resistive loads do not.
 
480sparky said:
You need three wires for 3-phase. You've only got two, so it's single-phase.
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Where did Chris say he only had 2 wires?

Two 5000 watt elements could be supplied with 3 phase.

Like you I also assumed a typical single phase unit but I think it was presumptuous to say '208 is not three phase'
 
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