Air compressor questions - electrical safety and mag starters

[VW_Buggsy]

I had a couple questions about my specific air compressor set-up. Hopefully simple ones.

I'm a DIY kind of guy and I got the compressor from craigslist. It came to me with a 3PH motor that I replaced with a single phase many years ago. To cut to the chase I want to:
A: Make sure my electrical path is safe and solid
B: Find out whether I should be using or would benefit from a magnetic starter

Current electrical set up from house breaker to motor:

• 40 AMP breaker (home builder installed)
• AWG 8-2 with 10 AWG ground (home builder installed) from breaker to socket
• 3 prong "dryer style" sort of plug and socket (10-30r/p) made for 220V
• 10 AWG 3-wire SJTOOW (300V service, Oil and Weather resistant) (TPE) for the plug cord
  • This cord runs from the plug to a 60A 240V 10HP (max) enclosed Square D switch that I use as an on/off switch
  • Then to a heavy duty pressure switch: HEAVY DUTY CONDOR USA PRESSURE SWITCH, 26AMP, 11GA2E, 100/125 PSI
    • I leave this in the "auto" position and switch VIA the Square D switch
  • Then to the motor: CENTURY AC Motor 5HP single phase 230V 22 amps (rated)
• lastly if anyone is curious this is powering a Speedaire/Champion 3Z180 2 stage splash lube pump head VIA dual V belts

I only run the compressor when I'm using it (it doesn't take long to pressure up) and shut it off and drain it at the end of the day so it's not always on. If any more details are needed for anyone willing to respond just let me know.

I have been running this set up for over 10 years, which would seem to indicate it's okay. The reason I ask is because I had to replace the original pressure switch (Was a Furnas unit that was fine for 5hp 3ph but probably underrated for 5hp 1ph based on labeling) about a year ago.

Also, my motor run capacitor went bad last week. When replaced, the motor still didn't start. I had to disassemble the motor and found that the contactors on the centrifugal clutch that transitions from the start windings to the run windings were pretty bad (pic below). I sanded them clean, reassembled, and the motor is running again.



Is it likely that something in my electrical set-up (particularly lack of a mag starter) caused or contributed to the contact points in the motor burning or the capacitor failing? Or perhaps the contact points were due to the capacitor going bad... or just simple age and wear all around? My understanding is the motor would be pulling the same amps either way but (while I know a little bit) I sure don't know everything. Replacing a motor of this size and quality would be pretty costly so I want to protect it as well as possible and set it up for longevity. I've been running things like this for a some time but if there is an issue with the set up that I can address before it is a bigger problem I'd like to do that before that happens.

Thanks to anyone that takes the time!

 

[Jswain]

The benefit from the mag starter would be it would take the load off your pressure switch and ensure that it wouldn't stick the contacts like you've already experienced. If your motor isn't thermally protected it could smoke the motor if it's not rated for continuous duty, or if the safety valves stick you could overpressure the system.

General consensus is if there is a red thermal reset button on your motor you don't NEED the mag starter, but it's benefits will always be there.

Sounds like you could easily remove the on/off switch you have now and put a mag starter in its place, then use the pressure switch as your on/off. Also most people don't recommend using a plug/outlet but better yet hardwired right to the mag switch, unless you need to be able to move the compressor. But unless you unplug it while running I doubt it will be an issue

 

[VW_Buggsy]

THANKS!

I do occasionally unplug it because I only have the one 220V outlet in my garage. I do some powder coating and I need that outlet to run my shop oven when I do so. I don't unplug it while it's running (nor do I usually flip the switch when the compressor is running unless there is an issue, I'll just wait for it to be stopped).

The motor is NOT protected, no reset switch. It IS continuous duty rated though. After looking more at motor starters that's basically their jam right? They are like a contactor relay but with the addition of an overload circuit that will shut down the motor if it starts to draw too much current, which sounds like a very good thing. When I was having issues I looked up replacement costs for motors and they are NOT cheap these days!

The pressure switch on-off is not easy to access with the way I have my compressor set up, it's kind of on the wrong side. That's one of the reasons I added the large on-off switch in an easy location. I suppose I could re-plumb the pressure switch on the front side if I had to.

If I replace the current on/off switch with a mag starter could I just get one with an on/off switch on the mag starter (it looks like they exist), or is it not best practice to use those on-off switches frequently?

Or could/should I simply wire the mag starter in AFTER the current on/off switch that I'm using? E.g. plug --> ON/OFF --> mag start --> pressure switch & motor set?

 

[TJMtl]

I have a big knife switch separating my compressor from my breaker panel.

 

[Jswain]

No problem wiring in the mag starter after the on/off switch

 

[Dagny]

A bleed resistor across the capacitor would reduce the arcing at the start switch.

 

[VW_Buggsy]

Thanks folks.

The motor came with bleed resistors on the start capacitors (3W 4.7k ohms).

After a lot more reading it looks like the fact that the motor doesn't have any overload protection built in alone is enough to justify adding a mag starter. So I'll be getting one.

I'm not sure it will help with the arcing but it'll add overcurrent protection and perhaps help protect the expensive motor a bit more.