What's new
What's new

Emeregency off switch for air compressor controls?

rons

Diamond
Joined
Mar 5, 2009
Location
California, USA
Emergency off switch for air compressor controls?

Air compressor powered by 7.5 Hp VFD.
VFD may be in a box or not, but it will be hung on the wall behind the compressor.
VFD is accessible but I have to walk a few steps around machine.
Electrical wiring in conduit, so it is not as easy as pulling a plug out of the wall to stop the motor.

Would something like a push-to-stop/pull-to-run or push-to-stop/rotate-to-run emergency switch mounted on the front of the compressor be a good safety idea?
The mushroom switch I have in mind also has a red light. So red light on when running and red light off when switch pushed.
 
Last edited:
All the VFDs that I have played with have an easily accessible Stop circuit, two terminals that get a normally closed switch connected to them. It would be simple to implement.

What situation are you envisioning that would require it?


Sent from my iPhone using Tapatalk Pro
 
I don't know what the rules in California are. I go by 25ft- that's what I was told was the max distance the disconnect can be from the machine.

An SO cord that can be unplugged counts.

So a breaker or safety switch within 25 ft. of the machine that cuts off all power, and it can't be obstructed.

Can't cite the code, but it's there somewhere...
 
All the machines in my shop have a lever operated disconnector in the power line. I like the colourful Lewden ones like this :- ISO-63 which can be found in a range of sizes with both yellow and grey fronts. Yellow for three phase, grey for single I think.

Big red lever is easy to see from a distance if a machine has power so it can be run and easy to grab to turn off if need be. Drilled for a lock off too. Hate the round ones which are, in comparison, unclear. Plastic case so hafta place them where they can't be bonked by something heavy. But thats good practice anyway.

Anything that hasn't got a clutch gets a big red stop button too. Usually the twist to release type so if its off it stays off until things are sorted and rational though resumed.

Clive
 
In the case of an air compressor, I would like the Emergency shut off as far away from the tank and plumbing as possible. The breaker panel would be fine. In fact, that is where mine is, right around the corner in the other room.

It's like keeping a fire extinguisher at the exit door., not at the fire place.

eta, I open the service panel breakers on all the VFD equipment whenever thunderstorms are in the area close by. Once burned, twice shy!
 
I have a breaker panel by the door. The compressor is on it's own breaker. Note that the NEC says the disconnect has to be visible from the machine it turns off. I guess that is so the worker can verify no one turned it on while he was working on it. I am not sure if a breaker is allowed to be considered a disconnect or not. Seems like it should be to me.
Bill D
 
I have a breaker panel by the door. The compressor is on it's own breaker. Note that the NEC says the disconnect has to be visible from the machine it turns off. I guess that is so the worker can verify no one turned it on while he was working on it. I am not sure if a breaker is allowed to be considered a disconnect or not. Seems like it should be to me.
Bill D

Where do you place the emergency shut off on your window air conditioner? Or the break room refridge? Both are electric motor drive compressors that run higher pressures than the air compressor does. Just saying the NEC might accept alternative switch placement in this case. Maybe not.
I have NEVER encountered an EMERGENCY shut down switch on an air compressor installation. Normal switch box disconnects, YES, Illuminated RED buttons, No.
 
both our compressors at work (big/med sized ir screw) have red off now buttons, not eliminated. If you hit them all power is off except the screen that just blinks fault, fault, improper shut down. These are IR buttons right on front of compressor, they kill dryer too.
 
Some sort of easily operated, lockable disconnect is nice.

At my old job they snapped a fitting off of an air compressor tank with a forklift and I was able to operate the disconnect from 15 feet away without approaching the potentially damaged tank or climbing over the forklift. A few months later the same compressor seized and the motor caught on fire.

At my home shop I have a decent 5hp Ingersol Rand compressor that occasional suffers from a stuck pressure switch.


If I were doing this I would put a physical disconnect switch prior to the VFD. Safety circuits are a last resort, as simple as possible way to shut down a machine. Without a physical contactor I don't really trust a VFD to process an E-stop command in all possible faults (without me looking into it much further). Besides, it's nice to be able to shut off power for sure for maintenance or repairs.
 
both our compressors at work (big/med sized ir screw) have red off now buttons, not eliminated. If you hit them all power is off except the screen that just blinks fault, fault, improper shut down. These are IR buttons right on front of compressor, they kill dryer too.

That was my idea before asking here. I will have a disconnect breaker before the VFD that drives the compressor.
 
If I were doing this I would put a physical disconnect switch prior to the VFD. Safety circuits are a last resort, as simple as possible way to shut down a machine. Without a physical contactor I don't really trust a VFD to process an E-stop command in all possible faults (without me looking into it much further). Besides, it's nice to be able to shut off power for sure for maintenance or repairs.

I was thinking about a motor starter and energized start/stop buttons. Except somebody had mentioned that you don't want to use a contactor before powering a VFD. Still wondering how that is much different than operating a manual breaker switch. If the somebody was thinking about excess contact bounce then I don't know what difference it makes. Have not measured the difference.
 
It is fine to have a disconnect before the VFD. But only turn it off when the VFD is off already. This will eliminate the chance of the VFD coming on while working on the machine.
You can switch off the supply power to the vfd when things are running and it will shut it down but..doing so risks the vfd will not have a feedback loop and it may fry itself. Probably more of a problem on the output end.
Bill D
 
I have never seen the need to have an emergency off for the compressor. A broken belt is not an emergency, a broken air line is not an emergency (and least turning off the compressor would have a slow effect). Do to my avoidance of noise in the shop, my compressor sits in another building and I would probably not be aware of an emergency situation (such as fire, or over pressurization).

Just some comments on some of the replies to the OP:

Contactors are fine on the input of a VFD but may be a hazard to the VFD if on the output. Also VFDs should power up in a non run mode. I do not think you can actually turn a VFD off.

Being 15 feet from a damaged pressure vessel would not give me any comfort unless there was a blast wall in that space.

I would be very concerned if I had a compressor that had a tendency to over pressure. I would replace the sticky device (contactor, pressore switch, etc) and possibly put in a redundant protection device. Hoepfully you have a good pressure relief valve.
 
Thank you for the replies.

I opened up my folder for the air compressor and found all the safety stickers I didn't want to apply all over the machine. Caution this, and don't do that, etc. Got me thinking about a emergency off button. Since I planned for push-buttons for draining water using Asco electric valves I got into button pushing mode. Trying to use what I have. The one at the lower right corner is a big honking GE with in/out stationary positions along with a red lamp. Some of you guys are right, the switch would just be sitting there looking all red and cool, but never used.

DSC_0702.jpg
 
To lighten the discussion of "STOP!" switches takes me back to when as broke college student, I worked 2 A.M. to 10 A.M. in a commercial bakery. When the bagging machine got a jam, within seconds, we'd be up to our waists in hamburger or hot dog buns. Someone would hit the stop, another would clear the jam and the rest would pick up the buns off the floor and put them into bags, on a tray, on the rack, on the truck and in the grocery store by noon. Think about that when you're having burgers this Fourth.

jack vines
 








 
Back
Top