Wiring up a 220V plug question

[Jim Koepke]

Take a look around your house Jim, I guarantee that there is a lamp or clock or some such with an 18 ga cord plugged into a circuit protected with a 15 or 20 amp breaker.

My comment was offering one reason to use an adequate gauge of wire in a circuit. It is to my knowledge not a matter of code or law.

In my experience more home shop and contractor equipment has created a display of smoke or fireworks than lamps or a standard wall clock.

jtk

[Kev Williams]

I know the differences between 120 and 240, but I could use an explanation as to why a 5000 watt hot tub heater with both ends connected to 120 volts becomes only a 1250 watt heater with one end connected to 120 and the other end neutral... simple question, why is the wattage quartered and not halved?

and-- won't this answer apply to the 16ga wire debate?





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[Frank Pratt]

I know the differences between 120 and 240, but I could use an explanation as to why a 5000 watt hot tub heater with both ends connected to 120 volts becomes only a 1250 watt heater with one end connected to 120 and the other end neutral... simple question, why is the wattage quartered and not halved?

and-- won't this answer apply to the 16ga wire debate?

This calls for a little math:
First, let's look at the operation at 240V. For a 5000W heater we need to figure out the current and resistance of the element.
To find circuit current: 5000W ÷ 240V = 20.83A
To find element resistance: 240V ÷ 20.83A = 11.52Ω
Now we'll connect that same heater to 120V:
Current: 120V ÷ 11.52Ω = 10.42A
Watts: 120V X 10.42 = 1250.4W

[Mike Henderson]

This calls for a little math:
First, let's look at the operation at 240V. For a 5000W heater we need to figure out the current and resistance of the element.
To find circuit current: 5000W ÷ 240V = 20.83A
To find element resistance: 240V ÷ 20.83A = 11.52Ω
Now we'll connect that same heater to 120V:
Current: 120V ÷ 11.52Ω = 10.42A
Watts: 120V X 10.42 = 12650.4W

Typo in your last line. Should be =1250.4W

Mike

[Frank Pratt]

Typo in your last line. Should be =1250.4W

Mike

Thanks Mike It's corrected.

[Jim Koepke]

I know the differences between 120 and 240, but I could use an explanation as to why a 5000 watt hot tub heater with both ends connected to 120 volts becomes only a 1250 watt heater with one end connected to 120 and the other end neutral... simple question, why is the wattage quartered and not halved?

and-- won't this answer apply to the 16ga wire debate?
.

It depends on the way the heater elements are designed. If there are two elements with only one of them having a center tap to allow for a 120V connection, that would explain it.

At half power, 2500 watts, it would be slightly above the limit for a 20 amp breaker in a 120V circuit.

jtk

[Frank Pratt]

It depends on the way the heater elements are designed. If there are two elements with only one of them having a center tap to allow for a 120V connection, that would explain it.jtk

The hypothetical heater in question would behave as discussed if it was just a simple single element heater. If you half the voltage, you get 1/4 of the full voltage heat.

[Curt Harms]

One other thought about European motors - what's the frequency? I recall discussions about European induction motors running at 50 Hz. I don't know if that matters to the machines in question or not (universal motors don't care I think).

[Mike Henderson]

One other thought about European motors - what's the frequency? I recall discussions about European induction motors running at 50 Hz. I don't know if that matters to the machines in question or not (universal motors don't care I think).

At full load a European 50hz two pole induction motor will run a bit less than 3,000 RPM (2,850 RPM), just as a 60hz two pole induction motor will run a bit less than 3,600 RPM (3,450 RPM). Because the European motor runs at a lower hertz it will normally have more steel in the stator. Normally, you can run a 50hz motor on 60hz without any problems. You may encounter problems (overheating) going the other way, running a 60hz motor on 50hz.

Mike

[But a European power tool may have pulleys that are calculated to turn a saw blade at a certain speed. If all you do is run the tool at 60hz you may be overspeeding the saw blade.]