kbsparky
Senior Member
- Location
- Delmarva, USA
You don't have to find the resistance here.
If you have a resistance load of 40 Amps@240 Volts.
Simply take the voltage proportion against the rated Amps:
208/240 = .86666 Now multiply that against the rated Amps of 40 = 34.666
To find out the new output in watts using the lower supply voltage, then carry it one step further: 208x34.666 = 7210 watts.
Rule of thumb when connecting a 240 rated heater to a 208 source = 25% drop in watts output.
This was the subject of one question on my licensing exam:
Volts/2 x Amps/2 = watts/4
2000 Watts divided 4 = 500.
.8666 Volts x .8666 Amps = .75 watts.
75% of 2000 = 1500 watts.
If you have a resistance load of 40 Amps@240 Volts.
Simply take the voltage proportion against the rated Amps:
208/240 = .86666 Now multiply that against the rated Amps of 40 = 34.666
To find out the new output in watts using the lower supply voltage, then carry it one step further: 208x34.666 = 7210 watts.
Rule of thumb when connecting a 240 rated heater to a 208 source = 25% drop in watts output.
This was the subject of one question on my licensing exam:
Using the formula of Watts = VoltsxAmps we can allocate proportions thus:Given: 2000 watt baseboard heater unit rated for 240 Volts.
Connect this same heater to a 120 Volt source.
What will be the wattage output of this heater so connected?
- 2000
- 1500
- 1000
- 500
Volts/2 x Amps/2 = watts/4
2000 Watts divided 4 = 500.
Now connect this same heater to a 208 Volt source. What will be the output in watts?
- 2000
- 1500
- 1000
- 500
.8666 Volts x .8666 Amps = .75 watts.
75% of 2000 = 1500 watts.