Residential Calculation whether to use 220 volts or 240 volts when dividing watts to determine the amperage

gunnpe

New User
Location
Washington State
Occupation
Commerical Electrical Inspector
Question: When determining the wire amperage size when tying in multiple forced air heaters, is 220 volts or 240 volts used when dividing into watts to get the correct amperage for sizing my wire in a residential setting?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Welcome to the forum.

I would use the stated power and voltage numbers to calculate the operating resistance.

Then I would calculate the operating power using the current at the actual applied voltage.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
It depends. If the voltage is 240 at the site and the unit is "X" watts at 220v then you have to do a little math to get the correct info for sizing on resistive loads
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
220.5 (A) Voltages.
Unless other voltages are specified, for purposes of calculating branch-circuit and feeder loads, nominal system voltages of 120, 120/240, 208Y/120, 240, 347, 480Y/277, 480, 600Y/347, and 600 volts shall be used.
 
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