Is a through-wall/window air-conditioner qualified for the application of the additional 25% rule when considering all motor loads in a overall service calc for single or multi-family dwellings? Or would the largest motor, instead, be, say, the trash compactor or the disposal (considering that they are lower in amps than the window unit, but are not combo motor loads)?
Largest motor, addl. 25%
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petersonra
Senior Member
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- Northern illinois
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- engineer
Re: Largest motor, addl. 25%
a window a/c is not in my opinion to be counted in your load calcs unless you were to hard wire it.
a window a/c is not in my opinion to be counted in your load calcs unless you were to hard wire it.
Re: Largest motor, addl. 25%
I am not sure that I agree that a window air conditioner should not be counted unless hard-wired. Many "fastened in place" appliances are cord-and-plug connected; ranges and dryers come to mind. In my opinion the air conditioner load should be calculated and, if it is the largest motor, then the 25% for the motor load should be added. Just my two cents and I stand ready to be corrected
I am not sure that I agree that a window air conditioner should not be counted unless hard-wired. Many "fastened in place" appliances are cord-and-plug connected; ranges and dryers come to mind. In my opinion the air conditioner load should be calculated and, if it is the largest motor, then the 25% for the motor load should be added. Just my two cents and I stand ready to be corrected
bphgravity
Senior Member
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- Florida
Re: Largest motor, addl. 25%
I agree with BOB. It just one more uncessary load to add into an already conservative calculation. If the installation called for several a/c units with each on an individual branch circuit, it would probably be prudent to include those loads into the calcs, but if this is just one a/c unit plugged into a general branch circuit outlet, I wouldn't worry about it.
I agree with BOB. It just one more uncessary load to add into an already conservative calculation. If the installation called for several a/c units with each on an individual branch circuit, it would probably be prudent to include those loads into the calcs, but if this is just one a/c unit plugged into a general branch circuit outlet, I wouldn't worry about it.
Re: Largest motor, addl. 25%
Very few (if any) window air conditioners are meant to be plugged into a "general use branch circuit". Most have a sticker on them, or a line in the owner's manual that says that the unit should be connected to an "individual branch circuit". The NEC is a MINIMUM standard. You can't say that it is conservative so certain requirements may be ignored. The NEC requirements are the bare minimum, they may be exceeded but you cannot do less than what is required. That said,if a service is installed that is so marginal that one window air conditioner makes a difference, then that is not a good design. I still don't see any way that a major load can be ignored just because it plugs in. If that is the case, when do you stop ignoring it? When it draws over 15-amps? When it is a 240-volt unit? When it has a heat strip in it? A load is a load and should be accounted for in your calculation. If the dwelling is also equipped with electric heat it may be ignored as a non-coincidental load, but that is the only reason I can think of.
Very few (if any) window air conditioners are meant to be plugged into a "general use branch circuit". Most have a sticker on them, or a line in the owner's manual that says that the unit should be connected to an "individual branch circuit". The NEC is a MINIMUM standard. You can't say that it is conservative so certain requirements may be ignored. The NEC requirements are the bare minimum, they may be exceeded but you cannot do less than what is required. That said,if a service is installed that is so marginal that one window air conditioner makes a difference, then that is not a good design. I still don't see any way that a major load can be ignored just because it plugs in. If that is the case, when do you stop ignoring it? When it draws over 15-amps? When it is a 240-volt unit? When it has a heat strip in it? A load is a load and should be accounted for in your calculation. If the dwelling is also equipped with electric heat it may be ignored as a non-coincidental load, but that is the only reason I can think of.
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- Semi-Retired Electrical Engineer
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