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Discussion Starter · #1 · (Edited)
Our instructor was telling us to divide the watts by 240. Why would you do that, as opposed to dividing by 120? I was thinking that dividing by 240 would give you a smaller number of amps, possibly resulting in an undersized wire or breaker. Also, wouldn't getting the watts for both the 120 and 240 parts of the appliance and adding them together work better? Then I again, I have never been on a job where the exact model of a given appliance was known during rough, so I guess people just run stuff for the usual case scenario. Thanks in advance.

ETA: Part of the title looks like it may have been cut off, though I'm on my phone and can't tell for sure. I'm asking this stuff in reference to 120/240 appliances.
 

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With a unit listed 120/240 you have to know what part of the load is 240V and what is 120V. In some cases like a range the 120V is just for lights and/or a fan motor
 
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Dennis Alwon said:
With a unit listed 120/240 you have to know what part of the load is 240V and what is 120V. In some cases like a range the 120V is just for lights and/or a fan motor
OK, so you calculate the current for each part and then add? That's what I was thinking, but we did not do it that way in class.
 

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OK, so you calculate the current for each part and then add? That's what I was thinking, but we did not do it that way in class.
I don't think the instructor did it correctly. If you have a unit with 4800 watts of heat at 240 and a 120 watt blower at 120V then you would have a current of 4800/240=20amp plus the blower 120/120= 1amp. Total load is 21 amps
 
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