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  #1  
Old 02-22-10, 01:00 PM
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Load question

In a 240v circuit, we have two hot wires (out of phase), one neutral and maybe a ground. The neutral wire can be of the same size as the hots because it will never 'see' more current than one of the hots, since they are out of phase.

Now then, let's say I have a 240v water heater with 4500 watt elements. That would be a load of 18.75 amps. Would it be correct that the two hots are each carrying 18.75 amps or are they each carrying half or 9.375 amps?
 
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Old 02-22-10, 01:21 PM
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If you are saying the water heater in question just has two hots running to it (no neutral) and...

...the water heater has two 4500 watt heating elements and...

...the water heater is a typical residential water heater wired so that ONLY ONE heating element will be on at one time*...

Then it would use 4500 watts at 240 volts and that would be 18.75 amps measured at either hot wire.

Here is a calculator for amps (use single phase)...
Power Calculators for quick conversions.

*Water heaters in a home are designed so that only one heating element will be on at a time. This is because everyone takes a shower in the morning at the same time. If both heating elements kicked on at the same time for a whole city, that would be HUGE electric load for the electric company. Also you can use smaller less expensive wiring.

Water heaters for a business/school/industry may be wired so both heating elements come on at the same time.
 
  #3  
Old 02-22-10, 01:46 PM
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Originally Posted by siearly View Post
In a 240v circuit, we have two hot wires (out of phase), one neutral and maybe a ground. The neutral wire can be of the same size as the hots because it will never 'see' more current than one of the hots, since they are out of phase.
If you had a neutral, then you would actually have a 240V/120V circuit as it supplies loads at both voltages. A pure 240V circuit has two hots and a ground.

Would it be correct that the two hots are each carrying 18.75 amps or are they each carrying half or 9.375 amps?
Each hot would be carrying 18.75A.
 
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Old 02-22-10, 02:18 PM
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You are referring to a 2-wire, 240 v , circuit which connects to a 2-wire load in the form of a heating coil with two connection terminals. The current-flow is similiar to connecting two pipes to a coil heated by hot water.

Suppose you use the hot-water in your Electric HWH (EHWH) to heat a room by connecting two lines from the EHWH to the coil or convector in the room which is heated by the hot-water from the EHWH.

If 10 gallons-per-minute "leaves" the EHWH in the "supply" line and flows thru the coil, then 10 GPM returns to the EHWH in the "return" line.The electric current-flow in the two wires of the circuit is similiar.

You have confused the issue by including a non-essential ( for this circuit ) conductor , the Neutral, in your question.
 
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Old 02-22-10, 04:09 PM
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Thanks much for the responses. You've answered my question.
 
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Old 02-22-10, 04:12 PM
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Originally Posted by Bill190 View Post
If you are saying the water heater in question just has two hots running to it (no neutral) and...

...the water heater has two 4500 watt heating elements and...

...the water heater is a typical residential water heater wired so that ONLY ONE heating element will be on at one time*...

Then it would use 4500 watts at 240 volts and that would be 18.75 amps measured at either hot wire.
You nailed it. Sorry for not being more clear.
 
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