Can someone please tell me how to correctly determine proper conductor size for HVAC equipment if you know the total running amps.
I need to know how to do this without any help from equipment nameplate info.
Example....Total running amps of condensing unit 16 amps. What size wire is required, and how did you determine?
Also a question about voltage drop.... A unit with a voltage rating of 208/230v...does this mean this unit can operate within a voltage range of 208-230v? And if so..... Is there an allowable voltage drop of +/- 10% on motors? Does this mean that a unit with a voltage of 187.2 - 253v (+/- 10%)????
440.32 requires that the conductors be rated for 125% of the branch circuit selection current or the rated-load current of the motor/compressor. Your example: 125% of 16 amps equals 20 amps. I would run #12 copper.
Voltage drop? No, that is the range of the voltages the motor will run at. These voltages are "nominal". The actual measured voltages will vary from these slightly. Yes this motor will operate at any voltage between these two. Motors will draw more amperage at lower voltages, but keep it within reason. The NEC suggests we limit the voltage drop to 3% from the nameplate voltage for reasonable efficiency of operation. Some motors and some motor applications could handle a VD of 10%. As the voltage falls, the motor will heat up more and more. It is a trade off, early motor failure or full voltages. Which is more expensive?
I realize that the equipment manufacturer usually provides this info on nameplates but, I needed to know how to properly do this without all the info.....just total running amps.... Incase all the info. wasn't provided.
I did get the 16 amps off a nameplate for an example.
The 125% rating for wire size and the 3% voltage drop was what I was after.
If total amps is 10.5 (10.5 x 1.25 = 13) I would use # 14 which is good for 20 amps but use a 15 amp breaker???
If total amps is 18.1 (18.1 x 1.25 = 22.6) I would use # 10 even though # 12 would do but, # 12 must use a 20 amp breaker.
I agree completely with wolfdog. Check out the new expanded code book that simplifies some of its answers. I would'nt touch anything before i had it all fiured out. For safety, oversize your wire a little if the name plate is not specific, if possible