Question on load calculations for service size with regards to air conditioners?

[jango]

My question is this: When figuring load calculations for residential electrical service sizing, say we have one air conditioner that shows on the name plate that it's actual draw is 20.2 amps at 240 volt. But its' maximum overcurrent protection is 40A. When doing my load calculation, am I correct in figuring it at 20.2 amps at 240V? or do I need to figure 20.2 x 125% for continuous motor load, or something else? Thanks for your help.

 

[dana1028]

You take the nameplate rating of 20.2A [at 240v] for the calc.

Later, you will include an additional load of 25% of the largest motor...typically the AC.

 

[stew]

you can use the mca rating on the nameplate due to the fact that the manufacturer has included the 1.25% calculation to derive that figure.

 

[curt swartz]

you can use the mca rating on the nameplate due to the fact that the manufacturer has included the 1.25% calculation to derive that figure.

For a single A/C unit that will work since the compress is probably the largest motor load in the dwelling. If you have multiple A/C units you want to add the full load current of all motors and add 25% for the largest motor.