Power mains question: wire gauge

I would, since the starting current is much higher.

"DaveC"

** Giant HUH ??

Such a motor normally draws around 3 amps.

... Phil

#12 is 1.6 mohms/foot. That's 0.32 ohms total. The short-circuit current from 220 volts is almost 700 amps. A half horse is only around

400 watts, about 2 amps. I'd use #14.

Up to 4.9 Amps, according to the 2011 NEC (Table 430.248). And that's all you have to provide in terms of feeder/branch circuit ampacity.

Hmmmm, did the OP leave off a 1 or has he a very inefficient 1/2 hp motor ??

Rheilly P

As another poster stated, 220V @ 15A is like 4.5 HP (Or VERY lossy)

Something is amiss somewhere.

Hmm, now that you mention it...

Lemme check my notes.

[OP]

Maybe OP dropped a leading '1'. A 1.5 HP 230V 1ph motor still only draws up to 10 Amps per the NEC.

There is s thing called "voltage drop". Voltage will drop in a wire running a long distance, sometimes so much, the device at the end will not operate!

The amount of voltage drop depends on the voltage, the type of metal used for the wire (copper / aluminum), the wire size, and the load in amperage at the end of that wire.

The internet has made this easy for you. Just search google.com for the words...

Voltage Drop Calculator

200' of 14AWG solid copper wire has a resistance of about 0.5 ohms, so if your locked rotor current is 15A, then the drop across the cable will be 7.5V when the motor first starts up, leaving 212.5V for the motor. No problem.

If your motor is about 80% efficient, then at full load it'll be taking about 466 watts from the mains, which is about 2.1A.

2.1A through 200' of 14AWG ohm will drop about 1.1V across the run, leaving about 219 for the motor. Absolutely no problem with 14AWG, so don't waste your money on what you don't need.

3.1 horsepower.

Thanks.

The rating plate on the compressor says 3.1 hp, 15A, 230V.

Yet I see that 3 hp @ 230v is 18A:

Won't the 14 ga. wire and 15A breaker be taxed?

Should I reconsider the 14 ga (upscale it to at least 12?) wire for this compressor?

Thanks.

Until the motor or compressor is replaced with a larger unit. Then all bets are off. It's cheaper to do it right the first time. You could even put a small breaker box by the compressor & run AWG 6 to it, to power other tools, as needed without starting from scratch.

That's a good idea. I'll talk it over with the owner.

But for now I want to settle on what size conductor to use if it's just to supply this one compressor.

Thanks.

If it's 1/2HP, now, it's unlikely to grow to >5HP.

Run several #12s, instead, when needed. It's cheaper.

Pull additional #12s in the future? I've had bad experience pulling additional conductors in a conduit with existing conductors.

If I misunderstand your statement, please try again. ;-)

Thanks.

Yet your original post said 1/2HP. Make up your mind.

That's high. 3HP is about 2.2kW, or 7A at 240V. Double it (motors aren't 100% efficient) and it's in the 15A area.

Yes. Use a 20A breaker and 12GA.

Go figure that you'd expect a different answer with a different question.

No. A bundle of a few 12s will make a nice oversized #10. The finished 'wire' will be stronger and more flexible too.

Of course, the return has to match. So you pull all 7 at once.

Two sets of 3 #12s and one #12 fault return. Seven wires.

Conduit?