electrical advice needed

[-Clayton-]

Originally Posted By: Gary Allan
Originally Posted By: -Clayton-
I will be cooling approx 500 sq ft with it


Ah. You like frigid air! Me too. Heck with that comfortable stuff. Give me relief.

I bet you can get the room down below 60F.
Yes we like it cold.

 

[chas3]

the intent of a circuit breaker (in your load center) is to protect the wiring not the device at the other end. if you run 14/2 then the biggest breaker would be 15A. drawing more than 15A on 14awg wire will cause the wire to overheat.

http://www.hometips.com/articles/sunset_books/complete_wiring/circuits/conductorcurrents029.html

wire length has something to do with ampacity. you should not exceed a 2% voltage drop per nec. i dont think this should be an issue but i dont know the run length.

http://www.stealth316.com/2-wire-resistance.htm

the easy solution? run 12/2 and stick a 15A breaker on it.

 

[MolaKule]

That usually means a 15 amp breaker in each "leg" of the 220 volt line(s). I.E, each line is 120 v to ground and 220 Volts across the two hot wire lines. Your AC probably uses 220 volts for the compressor motor and condensing fan.

 

[doitmyself]

Quote:
the easy solution? run 12/2 and stick a 15A breaker on it.


I was once told that 14 ga./15 amp breaker and 12 ga./20 amp breaker were designed to only be used together to protect the integrity of the breaker working.

In other words, using too big of wire with a 15 amp breaker might defeat it's purpose to protect the circuit.

Any truth to this?

 

[XS650]

No

 

[tom slick]

Originally Posted By: doitmyself
Quote:
the easy solution? run 12/2 and stick a 15A breaker on it.


I was once told that 14 ga./15 amp breaker and 12 ga./20 amp breaker were designed to only be used together to protect the integrity of the breaker working.

In other words, using too big of wire with a 15 amp breaker might defeat it's purpose to protect the circuit.

Any truth to this?




12awg on a 15a breaker is fine. If you were to install 14awg on a 20a breaker then potentially the wire would burn before the breaker would trip. The same idea as using a extension cord with wire that is too small for the load.

on a long length 15a circuit you would have to use 12-2 or the resistance would be too high resulting in a voltage drop and an increase in amps.

side note:
The NEC (national electrical code) is written and maintained by the NFPA (national fire protection association). The main reason for these codes is for fire protection and safety, not circuit design.

 

[chas3]

in some cases you might need to install a 15a breaker on 12awg wire.

length of wire, insulation types, number of conductors, conduit size, all contribute to the maximum safe current. this tells you how big your breaker should be to protect that wire from overheating. the breaker protects the wire.

http://www.paigewire.com/calculatorinstructions.htm

i dont exactly like the answers coming out of this calculator, but my nec code book is at work. there are some exceptions with regard to feeders i believe, but i dont recall them offhand.

 

[tom slick]

Quote:
i dont exactly like the answers coming out of this calculator, but my nec code book is at work. there are some exceptions with regard to feeders i believe, but i dont recall them offhand.


that calculator leaves a bit to be desired. If you use it to calc a 240v circuit in residential/farm it would be two legs if 15a 120v. if you enter 240v 15a single phase into that calculator then you are entering that each leg is 240v, that's incorrect but easy for a DIY'r to do.

 

[Gary Allan]

Single phase is a great misnomer. "Twin pole", if added, would make more sense.

 

[chas3]

typically i dont any calculator on the internet--i like living. i either use the nec or the pocketref. usually the pocketref -- it has a better index. if you dont have the pocketref, you should get one.

however, i cant post the contents of the nec or the pocketref.