I have to install a very long wiring run to a compressor. Here's the criteria:
1. approx 300ft from my main panel to the compressor
2. 220V motor, 1 phase, operating at 11.2amps at 10psi/60Hz.
1. is #10 AWG sufficient? If so, how can I be sure (where could I check in the NEC to confirm)?
2. do I need to do a voltage drop calculation?
3. Will my motor burn out because it's so far from the main panel?
4. what size breaker is required?
5. would you recommend anything else? (i.e. maybe lighting protection because it's so far from the main house??)
All technical advice appreciated.
On Mon, 20 Jul 2015 22:36:10 -0700 (PDT), firstname.lastname@example.org wrote:
Disregard my previous reply.
I am sorry I misread your question I thought you were saying 3000
10ga at 300 feet will drop about 8v. If you start with a true 240v,
you end up with 232 at FLA but the open question is whether you will
have enough to deal with the locked rotor to start it.
I have a 120v 1hp compressor and we couldn't get it to start reliably
at 150' with a 10ga cord.
You may end up with 8ga or larger to make this work.
8ga gets you 5v drop at 11a but we still need to know what LRA is to
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.
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
0ft using this calculator. Is that something to be concerned about? I wil
l TRY to find the Locked Rotor Amperes by contacting the manufacturer, but
not hopeful. Any other suggestions?
I may be way off base here, but have you looked into keeping the
compressor close to the power source and running 300 feet of air line to
This company says their aerators can be operated with 1,000 ft of air
Not practical in my case... i'm feeding 4 aerator heads from this one compr
essor. That would be a lot of hose spidering off in many directions.
Besides, my calcs show the voltage drop to be very small; the running curre
nt is 6amps meaning startup current is maybe 18amps (well within a 10awg br
eaker's capacity), and (unless I'm missing something) no respondant has rai
sed a serious technical concern.
On Tue, 21 Jul 2015 05:31:00 -0500, Home is where I hang my hat
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
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.
On 07/21/2015 12:36 AM, email@example.com wrote:
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...
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)
On 07/21/2015 9:02 PM, firstname.lastname@example.org wrote:
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
Seeing the nameplate for OP's actual motor would certainly reduce the
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...
On Wednesday, July 22, 2015 at 10:34:15 AM UTC-4, dpb wrote:
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. .
On 07/22/2015 8:33 PM, email@example.com wrote:
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.
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