10hp air compressor wiring
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  1. #1
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    Default 10hp air compressor wiring

    I just got a10hp single phase 80 gallon compressor, the specs said recommend breaker 60amps, so I used a 60amp breaker and 6/2 wire about 100 feet. The unit arrived and states in the magnetic starter, under 100ft must use 4 gauge wire and over 100ft must use 3 gauge wire, failure to do saw will cause capacitor and motor failure. Does anyone have any insight on this. To re run 100feet of 4 or 3 gauge is quite the project and expensive. Plus I used Romex which I don't think I can get that big so I guess I would have to do conduit and thhn. Thanks in advance for any info and help

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    home depot carries #4 romex. here's their 500 foot offer
    https://www.homedepot.com/p/Southwir...8205/202316202

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    A 10 horse single phase motor is a moose, and will pull moose like current on startup. If you add 100 feet of wire and its accompanying voltage drop to that equation you're going to have some serious starting problems. If it were me powering that load at that wire run length, I would do exactly as was directed by folks in the know. Redoing it might be a bitch and somewhat costly, but it will guarantee that it will work.

    Would it be out of the question to situate the compressor near the power source and run a airline to the shop...cheaper than wire.

    Stuart

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    Ya in thinking about moving it closer to the panel but definitely not an ideal situation, I just don't understand why it calls for s60amp breaker but 3 or 4 gauge wire

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    Ya that's 4 gauge 3 wire so I believe it's 3 wires and a ground I only need 2 wire with ground and that's 500ft 2100$

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    Good chance you will kill the starting caps with low voltage, and might overheat the winding's. The starting amps on a 10hp will be over 200amps for 3 sec or so...#6 is good for 60 amps. I would use the size 4 and move the air comp closer to the power box....Phil

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    Simple ohms law.

    Googlevoltage drop calculator.

    A number 12 wire is rated for 20 amps but has ampacity for maybe 30 but that is for short distance.

    Wire has resistance and current flow causes voltage drop.

    Your starting currents are going to cause your lights to dim.

    Sent from my SAMSUNG-SM-G930A using Tapatalk

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    What are the rated full load amps of the motor?

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    Does the compressor head really need to be 100' from the panel? The head and tank can be separated on compressors fairly easily. The tank can be anywhere there's an air line, and keep the head/motor near the power supply - and run an air line to the system. IMHO the time it takes to separate the tank and motor/head, then add more air lines is far more efficient/cheaper than running all that heavy gauge copper.

    That being said, I started my with a Harbor Freight 60gal (cough), but only because I happen to come across a sidewalk sale and the 1.5hp/60gagal was $200, factory reman, no warranty. That thing ran all day, 5 days a week for 7yr with zero problems (yes, ran ALL day to keep up with the media blaster, die grinder and machining/air tools). Finally the motor blew out due to one of the transformers blowing outside the shop. We never turned it off at night since the lines were so tight, would stay full all weekend if off. Well, when the transformer blew, the compressor just happened to need to fire up and was trying to on 110v single leg (neighbor wood shop called me Monday morning, frantic my shop was on fire). It fried so bad by the time the breaker popped, the shop was full of smoke and lacquer was dripping out the the motor vents. Stuck a 3hp 1ph 220v motor on until the head blew a valve and purchased a used reman Quincy 325 head. The 3hp ran that head for a few more years until the bearings wore slap out, so snagged a 7hp 3ph motor to replace it. Now the problem is the head runs at 400rpm with the biggest pulley I had (needed air, quick fix, so the pressure switch is set to 190psi and can maintain 90psi in the most demanding shop usage (80-90cfm @90psi for the vapor hone alone).

    With that being said, I can't even imagine the starting draw of a 10hp 240v 1ph motor 100' from service.

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    Before you spend more $ rewiring it the second time, I suggest you evaluate the utility transformer and wiring feeding your shop. If it's not large enough, it wont matter what size wire you use in the shop.

    Using NEC values: 10HP 1Φ 230V is listed at 50A, required minimum circuit size, neglecting voltage drop from the utility transformer to your location = 50A * 1.25 = 62.5A min wire size = #4Awg @60°C. When you factor in some voltage drop, the circuit will need to be even larger to compensate.

    Then consider the inrush starting current, fully loaded motors starting across the line briefly require 6-10x the running current. Piston compressors are hard starting loads, once they already have tank pressure the pump must overcome at startup. Minimum starting current will be around 50A * 6 = 300A, on the high end it could be 50A * 10 = 500A. If the service transformer don't have the capacity to get it started readily, 300-500A inrush, the branch circuit wire size won't fix that.

    For the service transformer, a typical residential 10KVA unit is rated at 41.6A @ 240V. Not enough to run that motor with no other loads. 15KVA is rated @ 62.5A just big enough to run the load steady state but not much overhead for getting it started. This needs to be considered before you spend more $. 25KVA transformer would be much better suited to get it running, and that is without much voltage drop from your utility source to your load.

    Just some food for thought.
    SAF Ω

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    While a minor point, unrelated to this gist of this thread, air compressors typically start unloaded regardless of tank pressure. This applies to piston and screw types..as far as I know.

    Stuart

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    Quote Originally Posted by atomarc View Post
    While a minor point, unrelated to this gist of this thread, air compressors typically start unloaded regardless of tank pressure. This applies to piston and screw types..as far as I know.

    Stuart
    Yes, but there's still that pesky heavy armature and compressor head flywheel that needs to get moving. I am sure many of us old-timers had that one machine that took some hand cranking to get going once in a while. :p My old Logan tool room lathe needs it depending on resting position of the motor and what RPM gear it's in to this day! lol.

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    If there isn't one already, fitting a thermal overload is a very good idea.

    They're a legal requirement on motors >0.5HP here down under for a reason.

    Aluminium might also be worth considering for this size and length.

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    Quote Originally Posted by markz528 View Post
    What are the rated full load amps of the motor?
    Would that be in the motor? There specs says start up is 80amps. I don't know why in there specs the don't state the recommended wire size. If your replacing a compressor it's unlikely you already have 3 gauge wire ran.

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    Thanks. So that's a lot if information that im not fully understanding of. So the first thing you would do is call the utility company? And ask them what exactly. Thanks again

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    Yes this had some kind of relief system u believe so it's not starting with a load if I understand that correctly

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    I did run it twice from empty on the 6 gauge wire I had already ran and I noticed no problems with lights dimming or any thing what. There garage is on its own 200amp service that I just had run from the street. The utility came out and didnt seen to have any concern I did submit a load form to them, but at the time didn't have the exact specs of this compressor

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    So I talked to Eaton the answer for now is a smaller pulley on the motor, it will make the load about the same as a7.5hp and u can use my 6 gauge wire that was already ran

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    Sweet! Nice simple solution.

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    Quote Originally Posted by Atlaslathe View Post
    So I talked to Eaton the answer for now is a smaller pulley on the motor, it will make the load about the same as a7.5hp and u can use my 6 gauge wire that was already ran
    Apples and oranges. Smaller pulley is absolutely no help with locked rotor currents.

    The full load amps (fla) is on the motor nameplate - can you post a clear picture of the nameplate?

    Your dedicated 200 amp service is a huge help in this scenario...........


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