Power mains question: wire gauge

I would, since the starting current is much higher.

Cant hurt. It would definitely help, in fact. multiple #14s to make each #10 would work better, keeping each segment electrically separated except at the nodes, giving a sort of Litz effect. At that gauge, you can get SPC too (Silver Plated Copper), reducing ohms per foot without increasing gauge above #10.

And you want a #12 return run for ground fault carriage too. A single piece would pop a breaker.

"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.

ance

make

considered what the skin deepth at 60Hz is?....

-Lasse

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.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com 
------------------------------------------------------------------ 
Just an armadillo on the shoulder of the information superhighway.

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.

--
JF

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.

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?

I've never seen a 240 volt compressor it a 1/2 HP motor 2 HP is common, and go on up as the capacity increases. A local business recently switched from multiple 2 HP 240 VAC 60 gallon compressors to a pair of 480 VAC three phase units with 120 gallon tanks that are set upi to run their entire production line from one unit. It was the old EDCO factory that Emerson closed a few years ago..

Cheaper? When did yo go over to the 'Do it any way but right' side?

It's not cheaper when the extra labor and increased material costs are added for doing the job more than once. If you didn't size the conduit for more wire, you'll have to rip it all out & start over.

Then there's the cost of a bribe to get the inspector to look the other way.

Well, then why stop at #6? Run 3KV and a distribution transformer. You never know.

Who uses 3KV?

I've seen a *lot* of 1/2HP motors used for power tools that can be wired either way.

Rather irrelevant.

I always do it the right way. The "right way" depends on the situation. I guess the "right side" is universal, though, but it's also right.

It's a *lot* cheaper. #6 is a PITA to work with. No thanks!

Now you're throwing in random costs.

OK, 300K.