Discuss Single phase compressor starter. in the Electrical Forum area at ElectriciansForums.net

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Hi there,

This is my first post, I hope you guys and girls may be able to help and please be patient haha.

I have been asked by a friend if I could wire up a compressor for him, now the compressor is second hand so comes with no information or paper work with it what so ever.
After trying to research the compressor online I have failed to find any information although it is a reputable manufacturer (snap on to be precise).
The compressor is single phase, the run current is stated at just over 16A however it says to be connected to a 30A fuse? Which I found confusing.
The compressor come with a 13A plug on the cable which was amusing but I was wondering should a DOL starter with overload be used or could a radial with a type C or D MCB be used along with another form of functional switch.

many thanks in advance, I hope all the information required is included.
please find attached motor rating.
 

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Hi George and welcome to the forum.
 
You will need to fit a 32amp commando style plug or hard wire it to an Isolator, the compressor should have all its controls self contained inc' overload etc so no need for external protection (you need to confirm this), if hard wired without plug/socket set-up you can use cable rated to the full load current then fit the 32amp suggested mcb, this may overate your cable but you can class as a fixed load (as long as your Zs complies).

The reason the mcb is alot higher is to cope with the inrush of the motor when it starts up, otherwise regular nuisance tripping would be an issue.

If you go down the plug and socket method then your cables must be rated higher than your mcb rating, but the flex to the compressor only needs to be rated for the flc of the motor.
 
I'm already very suspicious, they're claiming a Cos phi of 0.99 on a CSCR motor.....

Can you attach a photo or two of the electrical controls that are on the compressor already? I've given you full user permissions so you should be able to add pictures as long as the filesizes aren't too big (<500kb)
 
I will have a look to confirm that the motor contains the internal controls and use the commando socket method
Very helpful thanks, didn't realise the inrush current current would be so high.

why is it that this is suspicious? I will try to source a photo for you, there is some form of functional switch on the compressor itself.

cheers for the help
 
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I will have a look to confirm that the motor contains the internal controls and use the commando socket method
Very helpful thanks

I would take note of what Marvo pointed out, if you can add a pic' of the controls we may be able to advice further :)
 
I'm already very suspicious, they're claiming a Cos phi of 0.99 on a CSCR motor.....

Can you attach a photo or two of the electrical controls that are on the compressor already? I've given you full user permissions so you should be able to add pictures as long as the filesizes aren't too big (<500kb)

Morning guys, here's a photo of the controls on the compressor.. Thanks!!
Single phase compressor starter. image - EletriciansForums.net
 
I'm already very suspicious, they're claiming a Cos phi of 0.99 on a CSCR motor.....

Can you attach a photo or two of the electrical controls that are on the compressor already? I've given you full user permissions so you should be able to add pictures as long as the filesizes aren't too big (<500kb)

Morning guys, here's a photo of the controls on the compressor.. Thanks!!
Single phase compressor starter. {filename} | ElectriciansForums.net
 

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.........why is it that this is suspicious? ..........
I was referring to their claim that the motor presents an almost linear load.

I'm guessing that's just a pressure switch in the photo and maybe has a built-in off loader. Does the supply go directly into that pressure switch and then a short cable direct from the pressure switch to the motor? If so you'd need to incorporate a manual motor starter into the supply after the isolator / commando socket.
 
Okay I see, excuse the naivety I have little experience in this area however it interests me!

I believe that it is just a pressure switch and it also has a short cable leading to another terminal box with the capacitors ect in it so i shall have a look into the manual starter route,

Thanks for your help!
 
You can either go with a manual motor starter if you're installing an enclosure otherwise a basic DOL starter would do the trick.
 
I was referring to their claim that the motor presents an almost linear load.

I'm guessing that's just a pressure switch in the photo and maybe has a built-in off loader. Does the supply go directly into that pressure switch and then a short cable direct from the pressure switch to the motor? If so you'd need to incorporate a manual motor starter into the supply after the isolator / commando socket.

Thats exactly what it is marvo usually set to stop motor at 7bar and restart at 6 bar (adjustable) with intergral unloader so motor starts with compressor under no load.
The red button is the stop start switch and the compressor will function better if stopped and started by this control. Putting in other switchgear could cause the motor to start under full load
 
Yep, a manual motor starter would probably be better because it just offers LRA/overload protection but you could use a DOL starter and use the pressure switch contact wired as a remote start signal rather than the pressure switch switching the full motor load.
 

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