[agoolay]

Hi new here, so bear with me. I'm trying to learn my calculations for a contractors test. When filling out the calculation table for a service load, how do you calculate when you have no ideal what size of heat and air unit is going to be installed? You call the H&A people up and they give you BTU's (which tells me nothing) and then they finally tell you "You need to run a 60 amp circuit to the heater and a 30 amp to the A/C unit". Would you just use the full wattage capability of a 60 amp circuit for the calculation?

 

[MDShunk]

You can convert BTU's to amps if you want to. 12,000 BTU's per ton of refrigeration. 1 horsepower per ton. 746 watts per horsepower, etc. etc.

Lacking that, yea, sure... go ahead and just extrapoloate the breaker values they gave you into your calc. What little that it's off, (a tad high), won't really effect your service calc much at all.

 

[brian john]

Contractors test? = masters ?

Marc:

I have always thought the residential calculations for a single resident were a joke. Because no matter what you calculate 99% of new homes get a 200 amp service or 400 amp. If you ever do a load monitor on the house it seldom ever reaches 30-40 amps (excluding electric heat or AC load)

 

[MDShunk]

I have always thought the residential calculations for a single resident were a joke. Because no matter what you calculate 99% of new homes get a 200 amp service or 400 amp.

Yeah, I agree, but it forms the foundational skill for unusual homes and light commercial work. Small home with gas appliances = 100 amp. Regular home without electric heat, or small home with electric heat = 200 amp. Large home = 320. Apartment buildings are about the only time I do a service calc anymore, unless there's something unusual about a certain home that causes me to 'double check' my gut with a service calc.

 

[brian john]

I agree 100%. And how else could they complicate a test without the one problem that always has a calculation that works out to 149 amps or 151 amps?