question about 300ft long wiring run

Buy a couple of transformers and do it at 480v.

Voltage drop will kill you if you just try to do it with more copper

Disregard my previous reply. I am sorry I misread your question I thought you were saying 3000 feet.

I'm using #10 for 85 feet. That's works ok. Its even 120volt probably more current. Never measured. I don't know the hp rating of motor. It has a 3 hp equivalent rating. The compressor may have a breaker specified. That said, without calculation, your cutting it close.

Greg

Plug ur numbers in and click to calculate ... 11.2 amps at 10 psi? Probably ought to consider what it is at 150 psi.

Sorry, I should have mentioned: it's a compressor for a pond aerator, so I don't expect very high pressure/load at all. Looks like an 8V drop over 30

The current draw will be less at the top of the pressure range than it is in the middle. I plotted the curve of my compressor and it is a bell curve. That may seem counter intuitive but the compressor is simply free spinning at the top of the pressure curve because it is not moving much air. An example is your vacuum cleaner. If you block the hose, the motor speeds up because the load drops.

That is a big honking aerator. It sounds like 2HP or so. Are you sure you are not looking at the 120v FLA?

...

Agree w/ gfretwell that seems like awful big load for an aerator; how about a link to the particular unit you're planning on?

Given the figures above, the motor-sizing table in my copy of Richter's Wiring Simplified shows a #6 for 350-400 ft run 240V 2 and 1-1/2 hp, respectively. That's based on a 1-1/2% drop calculation for motor vis a vis the nominal 2% considered "standard" for other non-motor loads.

If this really isn't hard-starting, #8 would be marginal at 230-280 ft max distance for the two motor ratings above.

W/O further details, looks like #6 to me although probably could get by w/ #8. #10 is definitely too small for that size motor load...

#10 would probably suffice for the running load, but the starting load will be much greater. I would go with #8 copper wire. You should contact the manufacturer and see what they recommend for a wire size and a breaker.

Check out article 430

John Grabowski

On 07/21/2015 1:29 PM, dpb wrote: ...

at that distance.

Manufacturer FINALLY got back to me this evening! It's 11.2 amps at 110V, so only 6 amps at 220V. That said, I used the above website to calculate the voltage drop at 8volts over 300LF. This is 3.5%, which I beleive is quite acceptable.

I think I'm good, yes?

(all technical opinions greatly appreciated, especially dissenting ones)

That makes a lot more sense on the motor size. Now the question is, is it a dual-voltage motor?

That's too much for a motor circuit if that's what you computed for the running voltage; you'll be way under that during starting.

The table again shows you can go 340-ft 240V for 1/2 hp w/ #10 but only

I'm saying you need #10.

This sounds like a 1HP motor so I would go after that in your table.,

Yes, it's definitely a dual voltage motor. Yes, you are correct in that my voltage drop calculation is incorrect (used the wrong current) and I just redid and found only a 4.5volt drop (2% drop). Yes, I plan on going with #10.

Thank you, evereyone, VERY much for the advice, all of which was well-referenced and thought out.

Realistically, it's likely 3/4 hp; the table for it would be 240-ft for #10 so would also need #8 for 300 to be within the 1-1/2% drop range it uses.

Seeing the nameplate for OP's actual motor would certainly reduce the guesswork...

As a last point (altho OP is likely long gone)...One can never go wrong going up a size and just a quick survey showed #8-2 UF is 1.80/ft whereas #10 is 1.60, 0.20/ft difference. That would translate into $60 for the run difference. Difference likely to be less than that in quantity but if have no use for the extra and don't want to go to the trouble of reselling the end, might choose to but the length needed...

Wait... I'm still here! (the OP) This photo is the _same_ model that I have:

It's a 1HP motor, but I can't understand much else from the sticker. Any additional advice or instruction appreciated. .

OK, thanks....if it's really 300-ft, I'd definitely run #8. Doesn't give LRA and I didn't try to find more detail spec's via the part no but can't go wrong by the larger size as noted above. If nothing else, it'll run a tad cooler and you won't need to worry about starting effort shortening life by being marginally under-voltage.

The motor is 1 HP. If wired for 115 volts it takes 23 amps and if 230 volts it takes 6.5 amps.

If ran on 60 hz it runs at 1723 rpm and if 50 hz 1425 rpm.

It has a thermal switch inside so if it gets too hot it will stop and when it cools down it can be restarted.