3ph air compressor wiring

[green-hornet]

I have been asked to look at a foreigner job, wiring an air compressor.

The factory I use to do some work for when I was a sole trader has just acquired a second hand 3ph air compressor, when I went to look at it the connections had been cut at source, there is only two connections, one is the feed to permo run the compressor, the other is the valve stop, or auto stop. I assume it works by user on/off (at workstation), then the compressor auto stops when up to the set pressure, then auto starts when below another set pressure.

Now here is my problem the control was left in the building, and is now gone with the rest of the building, its old but works fine, I doubt the old controller would be up to standards anyway. I would like the controls to be to current regs, and would appreciate any help or links to the type of controller I would need to fit, I am unsure about the amps it runs at, never thought to check but would assume not a great deal.

 

[Sidewinder]

G-H,

I guess you mean something like this, but 3ph & industrial?

Clarke Pressure Switch 1 Port 20 Amp Single Phase - Machine Mart

You can acomplish almost the same thing with a pressure switch & a DOL starter easy with 1ph, a little trickier with 3ph, you may need some more bits.

The main Q is if you need a decompression type device on the compressor for starts?

 

[androiduk2002]

Is it a belt drive or a rotary screw ?

 

[Riggy]

GH if it's an oldish machine, it may well be designed to run the motor all the time (generally via a D.O.L starter as it doesn't start under load) and control the on/off load via a solenoid and unloader valve(s). If this is the case you need to look a bit harder for a suitable pressure switch as you need a N.O. (i.e. close on high pressure) contact to energise the solenoid to unload the compressor. Hope this makes sense!

 

[green-hornet]

I had to jump ship shortly after posting last night, family business.

Anyway the compressor is fitted with a pressure sensor on the outlet line, when up to pressure this will auto stop the motor.

Its definitely a D.O.L, the pressure switch is a NO contact, the problem I have is how to wire this up with the pressure switch to a remote station, probably at the workstation, I thought of just a contactor but would this comply with the regulations, the feed would be protected by the BS88 fuses, the machine will be about 40 m away from the operator, I could put another isolator within 2m of this operator though with no problem.

 

[Andy™]

what about a normal start/stop contactor at operator/other, and another contactor at the compressor, with coil through pressure switch?

 

[green-hornet]

I have thought of that Andy, but I am sure to comply with the regulations there should be a pressure indicator/alarm at the station so any emergency action can be taken, I have not done any machines for ages, and the last few I did was just to replace the brakes or motors.

 

[Andy™]

run a signal back to some neons at push button control for 'on' & 'run'

 

[Sidewinder]

G-H,

You'll need a control transformer mate along with primary & secondary protection on this.

I would put all the control gear at the compressor with a remote start/stop, it can be done with 4 cores including earth.

You will obviously need a main isolator, though that can be at the machine/control panel.

The remote buttons don't need their own isolation really they just need durable labelling wrt their purpose.

I would suggest you should have local & remote pb's for the machine.

Also if you run the control at the machine then your cable losses are minimised as the big load is all controlled locally to the motor.

Are we getting there?

The main DOL idea with a secondary contactor for the pressure switch seems at the moment in my condition to be OK!

 

[green-hornet]

Now that sounds like a plan, if I get a chance in the morning I will take some pics, I did a test run with it direct from supply (fused of course) and it may be old but its a good one. I know pictures speak a thousand words.

 

[Sidewinder]

Just read Andy's post, I would probably use an illuminated start pb at the remote station too thinking about it.

You need to consider 602004-1 & PUWER98 as well as EAWR89 & MHSWR & 7671 (though 7671 is borderline in this case imho)