Technical NEED NEW SHOP AIR COMPRESSOR

""For figuring supply breaker size if all you have is horsepower, use 750 watts per HP, then divide by supply voltage; this will give you running amps. Multiply that number by three to get breaker size. This is to allow for current inrush when starting the motor. Generally speaking, supply breaker size is 300% of the nameplate running amps; a 5 HP motor will require a 50 amp breaker (and 50 amp wire). This will be true for all single-phase motors."" (crazy steve)

My compressor is a Puma, 5hp, two stage, 80 gal tank rated at 18cfm at 90#..Model TN5080VM..Motor is Leeson, 1740 rpm, 208-230v..FLA is 23-21 amps and SFA is 27-24 amps..Came with an mag starter wired in..... On-off switch is built into the pressure switch..Wire size between the starter/pressure switch is #14 and between the starer/motor is #10.. I do the math [per above quote] and end up with 51.13 amps..so that means like #8 or 6 wire...So since I wired it 30a breaker and #10 wire where am I in the scheme of things?

 

[QUOTE="seb fontana, post: 12336843, member: 8107] ...So since I wired it 30a breaker and #10 wire where am I in the scheme of things?[/QUOTE]

Well, there's multiple things going on here. First, that #14 wire from the pressure switch is fine as all it's doing is operating the starter load. Technically, the #10 is too small but if it's part of an 'approved assembly' and UL listed, it's fine. The thing to remember is the listing labs don't care about functionality, all they care about is that it doesn't present a fire and/or personnel hazard under normal designed use. It's up to the manufacturer to warranty that it will actually work. If that #10 was field-installed, it would be illegal. It's also worth noting that when using non-listed electrical equipment, if it fails and causes a fire, your fire insurance may be voided. Always look for a UL label.

Second, if it's operating OK on that 30A 2P breaker (no nuisance tripping during extended use or when starting), you're good to go. But that does tell me that it's '5HP' rating is very suspect, as are the nameplate amp numbers. Unless the mag starter also has some sort of 'soft start' circuitry in it; with the price of electronics continually going down, this technology is starting to show up in consumer stuff. I'd be very curious to see what the actual running amps are; find that out and you can calculate the actual HP.

 

Well, there's multiple things going on here. First, that #14 wire from the pressure switch is fine as all it's doing is operating the starter load. Technically, the #10 is too small but if it's part of an 'approved assembly' and UL listed, it's fine. The thing to remember is the listing labs don't care about functionality, all they care about is that it doesn't present a fire and/or personnel hazard under normal designed use. It's up to the manufacturer to warranty that it will actually work. If that #10 was field-installed, it would be illegal. It's also worth noting that when using non-listed electrical equipment, if it fails and causes a fire, your fire insurance may be voided. Always look for a UL label.

Second, if it's operating OK on that 30A 2P breaker (no nuisance tripping during extended use or when starting), you're good to go. But that does tell me that it's '5HP' rating is very suspect, as are the nameplate amp numbers. Unless the mag starter also has some sort of 'soft start' circuitry in it; with the price of electronics continually going down, this technology is starting to show up in consumer stuff. I'd be very curious to see what the actual running amps are; find that out and you can calculate the actual HP.[/QUOTE]

It has run ok, only used it once when I did some outside sand blasting for a couple hrs..Otherwise I run my old 4hp single stage as I don't do much with airtools...

 

Buy the biggest American made pump with the biggest tank possible so that that the pump is rebuildable when the time comes.

I picked up an Industrial Gold Series 120 gal, 4cyl, 2 stage that needed a motor off of CL for $400. I put a 10hp 3ph motor on it (shop has 3 phase coming in & Ind. Gold sells this setup) that was "freshly rebuilt" locally and a brand new mag starter and total investment is around $750-$800. It's big and bad... but we NEVER run out of air!!! Best investment ever. Originally, the compressor was a single phase 7.5hp (motor was gone when I got it) compressor, but if you look that manufacturer up, that's the smallest compressor that pump comes on and it has a wide range of performance based off of motor RPM & pulley size (which there's a ton of options of). Go American! Go BIG!

 

We had a 40 ton GE railroad locomotive that had 2 engines and 2 air compressors, 1940s vintage. We had to replace one and purchased a Quincy compressor pump only that cost almost $3000 and was a 5 hp 2 stage unit. One of the differences you will find in compressors are that some are splash oiled and some use a pressure oiling system like Quincy so they should last longer. I don't know if they are still made in the US as most manufactures at least make parts in other countries and might assemble them in the US.

Is it worth paying many times the price of a cheaper compressor? For me, if I can buy one that will last 10 years for $200 instead of one that will last 30 years for $2000, I'm going for the $200 one.

In a shop setting, if you are constantly using a high volume of air, a large compressor might be the best, but 2 smaller compressors might work as well. If you only have occasional use for a high volume of air, two smaller compressors are much more economical. It's like you might haul a heavy load once a week but it doesn't make sense to drive a semi truck and trailer as a daily driver. You can set up the larger one to turn on at a slightly lower pressure than the smaller one or have two the same to have spare parts. Maybe have a more expensive, more durable compressor for constant use and a cheaper one for occasional use to supply more volume.

If you have a business that is dependent on an air supply, It would be wise to have more than one compressor. Don't put all of your eggs in one basket.

 

I like these thoughts and do have another 5 hp 2 stage old style iron compressor with a motor and a 60 gallon tank. The large bore cylinder had gotten water in it and was pitted badly in the bore. Disassembled it, got the cylinder bored and sleeved back to standard, but never got any further with it before I bought the Eaton that I have yet to install to replace the Gardner Denver. Have thought of finishing it up and wiring and plumbing it into the system to use when needed for high air demand or if the other unit failed. But like a lot of other old stuff I have in my shop at the age of 80, and still trying to keep 2 hot rods going, I'll prolly never get around to it.
But I do also have one of the "5hp" Back Max Sanborns back in the corner that I got in a deal for a spare