Compressor hand switch

eddiemeddiem · Jan 7, 2015

So I grabbed a 80 gallon, 5 hp, 2 stage compressor from the Zoro sale last week. It was delivered today, and arrived fast.

I'm in the process of deciding how I want to wire it up. Currently I have the 220 in my garage fed though a knife switch to an outlet where I plan to plug in the compressor (and my welder, etc). The issue is that the knife switch isn't too easy to reach, so I'd like to mount an on/off switch locally on the compressor so I don't have the difficulty of accessing the knife switch every time I want to just turn the compressor on or off.

The compressor motor is rated for 22 FLA, and the pressure switch doesn't have its own hand switch. So, I was looking at this nice/clean looking type of switch that I could easily wire up in a box, but it's only rated at 20 amps at 220V:

POWERTEC 71008 110/220V Single Phase On/Off Switch https://www.amazon.com/dp/B00KPEFL2I/?tag=atomicindus08-20

Is there any similar switch that's rated for at least 22 amps, or should I go with a contactor? It wouldn't be an issue to use a contactor with a 110V coil and plug it in elsewhere, I just haven't seen a nice small enclosure for a standard contactor... Do they exist?

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66dave · Jan 7, 2015

Hey bud-that is only rated for 20A@220v. Why not place a box with a single breaker in it?

Congrats on the compresser!

66dave · Jan 7, 2015

As far as contractors go check out the units they place on woodworking equipment...

rcjoy · Jan 7, 2015

Use a magnetic starter with an easy to access remote switch.

eddiemeddiem · Jan 7, 2015

I considered a box with a single breaker... I may go that way, I just like the asthetics of a green and red switch better.

Any examples of contactors on woodworking equipment?

I saw some magnetic switches, but those are in the $100 range...

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srmofo · Jan 7, 2015

eddiemeddiem said:
I considered a box with a single breaker... I may go that way, I just like the asthetics of a green and red switch better.

Any examples of contactors on woodworking equipment?

I saw some magnetic switches, but those are in the $100 range...

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I used an outside hot tub switch. IIRC it was like $15 at home depot. I ended up removing the weather cover before installing because I didnt like having to open every time I wanted to shut it off or on. Not as pretty as a red green switch but it was cheap and does the job.

66dave · Jan 8, 2015

Here is a cheap one that will handle 25amps for $85

http://www.grizzly.com/products/Magnetic-Switch-Single-Phase-220V-Only-3HP-21-25A/T24101

66dave · Jan 8, 2015

The magnetic contractors are at the bottom of the page. Also note that the magnetic contactor also adds a level of safety, if the unit is "on" and the power gets cut then the power gets turned back on the unit will stay "off" until you push the "on" button again. This is handy of all power equipment incase you stick your hand near the moving parts. Obviously we all say that never happens, but...

rlitman · Jan 8, 2015

Just to be clear, you need a switch that is rated for the horsepower of the motor AND the FLA. Just something rated for the current is insufficient.
I used an air conditioner disconnect for my compressor.

66dave · Jan 8, 2015

Rlitman brings up a good point, this is due the the electrical efficiency of the motor.22fla is a ~80% efficient 5hp motor. Don't assume all 5hp motors pull the same FLA as a 50% efficient will take ~33amp. Remember 1hp=755watts at 100% efficiency. So 755watts/hp *5hp= 3775watts...3775 watts/220v=17.5amps at 100% efficency, so 17.15amps/80%=21.5amp is your FLA, rounding up to 22FLA.

eddiemeddiem · Jan 8, 2015

Yeah, the nameplate states 22 fla. Generally, motors are rated for continuous duty at 80%, so this agrees with everything you guys are saying. I think the cheapest way out may be to just go with a disconnect/knife switch, or just stick with the one on the wall.

However, I'm still considering a contactor with a nice red/green push button switch. What type of enclosure are contactors usually housed in, they don't seem to google very well...?

catalytic · Jan 9, 2015

rlitman said:
Just to be clear, you need a switch that is rated for the horsepower of the motor AND the FLA. Just something rated for the current is insufficient.
I used an air conditioner disconnect for my compressor.

^^ This. Motors will draw up to 5x the nameplate amps during startup under compressor loads, so you need a motor rated switch or (better yet) starter. Look up the NEMA motor ratings -- you probably need a NEMA 2 starter. Case in point, I have many NEMA 1 switches that say 30A at 250v but are only rated to 2 or 3hp. Does your motor have overload protection? You want this on a switch/starter, and you _really_ want it if your motor doesn't have it already. You're probably exceeding the rating of your current knife switch.

A mag starter with appropriately sized heaters would be better than a motor rated switch, both for additional motor protection and so you don't get accidental restarts after power outs. This option is more expensive, though. You can also build your own with the appropriate relays, but this requires more knowledge. Picking up a NEMA 2 starter on ebay would be much easier IMHO. You can use one made for 3-phase -- you'll just use 2 of the 3 legs.

lmalcomb · Jan 9, 2015

http://www.amazon.com/dp/B002MPQ51O/?tag=atomicindus08-20

PT Doc · Jan 9, 2015

lmalcomb said:
http://www.amazon.com/dp/B002MPQ51O/?tag=atomicindus08-20

these come up to 60a disconnect I believe. I have one and it is great.

rlitman · Jan 9, 2015

lmalcomb said:
http://www.amazon.com/dp/B002MPQ51O/?tag=atomicindus08-20

Nope. On single phase, that switch is only rated for a 2HP motor.

lmalcomb · Jan 9, 2015

rlitman said:
Nope. On single phase, that switch is only rated for a 2HP motor.

http://www.leviton.com/OA_HTML/ProductDetail.jsp?partnumber=MS302-DS&section=40132 if You READ CLOSELY, the 2hp rating is for 120 volts ac, at 240 ac volts it is indeed 5hp :rocker:

rlitman · Jan 9, 2015

lmalcomb said:
http://www.leviton.com/OA_HTML/ProductDetail.jsp?partnumber=MS302-DS&section=40132 if You READ CLOSELY, the 2hp rating is for 120 volts ac, at 240 ac volts it is indeed 5hp

Ah, much better. That part was obscured in the picture on Amazon.

C96 · Jan 9, 2015

Hold everything now; unless I’m missing something here, I think you guys may be overlooking a potential problem doing this.

Depending on how the compressor is built, simply installing an on/off switch regardless of how it’s done (mag starter etc.) may be putting the compressor in harms way. If the compressor does not have a centrifugal unloader valve and is dependant on the pressure switch for unloading the head this will not work correctly. Should you turn the compressor off before it has reached its shut off pressure and the head pressure has not been released the compressor (when turned back on) will struggle to start again under the head pressure. This can cause excessive stress on the motor and will most likely cause an overload thus tripping the thermal protection device and or trip the circuit breaker.

eddiemeddiem · Jan 10, 2015

The motor already has overload protection, so a full motor starter with heaters isn't necessary but won't hurt. I do like the idea of a magnetic switch though.

The knife switch I have is sufficient for the outlet. Generally, switches, cables, and your typical household breakers aren't sized for inrush or when the motor is accelerating against locked rotor... They're sized for continuous duty. The reason is that inrush and locked rotor acceleration only last for a short period (a few cycles and a few seconds) and not enough heat builds up to do any damage or trip the breaker. If you have a breaker where the curve can be programmed, it's a different story.

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bsaint · Jan 10, 2015

eddiemeddiem said:
The motor already has overload protection, so a full motor starter with heaters isn't necessary but won't hurt. I do like the idea of a magnetic switch though.

The knife switch I have is sufficient for the outlet. Generally, switches, cables, and your typical household breakers aren't sized for inrush or when the motor is accelerating against locked rotor... They're sized for continuous duty. The reason is that inrush and locked rotor acceleration only last for a short period (a few cycles and a few seconds) and not enough heat builds up to do any damage or trip the breaker. If you have a breaker where the curve can be programmed, it's a different story.

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Exactly. There is a reason why motors aren't ran directly off breakers.

PT Doc · Jan 10, 2015

The op has a brand new compressor. He wants a switch and the leviton is rated for the hp of the compressor. I personally would never shut a running compressor with the leviton switch. I always use the compressor on off switch then when done just for an extra measure, I flip the leviton switch, well most of the time I remember. I'm not sure about code, but if your compressor switch failed for some reason having another switch close by could be very helpful.

sberry · Jan 10, 2015

Run a new wire for it.

Compressor hand switch

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