32 replies to this topic

[mm man]

This is what Clark recommend for there compressors

 7EE4345F-7E7D-4257-BEB0-EA0CA5DE3269.png   258.07K   6 downloads

[Homersimpson]

 

 

You will need a 32Amp type C MCB and a 16 Amp plug to cure that problem.

 

Been there, done that and that will cure your problem. If you can you need a stand alone circuit for the compressor. On initial start its a high load which blows the 13 Amp fuses.

 

When i bought my first 100ltr 3 HP compressor from Clarke i had a row with the Manager at the Peterborough Branch of Machinemart after their Tech assist guys on the phone said that was the problem. i argued back and said their instruction manual said a standard 13Amp 3 pin plug was fine. They went on to say the manual was incorrect.

 

I then said this to the manager and he said No they were wrong. Will guess what, i took their tech guys advice and have never had an issue since.

You need to be careful as a 16A commando socket has no fusing in it and therefore if its fed from a 32A MCB it could start to melt before the circuit breaker trips.

 

What you need is a 16A MCB with either a type C or D curve (rather than the domestic type B curve).  These circuit breakers allow a higher inrush current but will still provide protection of the correct size.

 

To go further into this what you should actually do is measure the value of Zs at the end of the cable with an earth loop impedance tester and use that to work out the prospective fault current, this then allows you to check whether the circuit breaker complies with the IET Wiring Regulations, of course if you have an RCD in the circuit then it almost certainly will.

 

 

As i mentioned mine is a 32 Amp Type C and yes there is also a RCD in my consumer unit at home for the garage ring main, another RCD for the household electrics and also at the workshop.

 

The problem is that you shouldn't just feed a 16A socket from a 32A circuit breaker as it contravines the IET wiring regulations and could be dangerous as you are not adequatly protecting the circuit against overload.  The RCD only covers faults to earth and if you put 1000A through the circuit as long as it passes down the live and back up the neutral the RCD will be happy until it melts.

 

Its one of those you get away with it until its a problem, (a bit like the screw driver bit in place of the fuse in my spot welder )

 

Its far better to use the correct size circuit breaker with a corse MCB (like a type D) as this will withstand the inrush better but will trip if the circuit is overloaded for a longer period.

 

I must go and order the proper socket for my spot welder and practice what I preach!

[Chris M]

Seems like I’ve stirred up bit of a hornets nest here! I called machine Mart today & they ‘off the record ‘ agreed with trying a 16 amp fuse. Trouble is you can’t get a 16amp fuse to fit a plug socket.
I also called the help line/ repair & they suggested replacing the plug socket with a new one as it could have a poor fuse holder?
On my way home I bought a new plug & a big pack of 13 amp fuses. Before I cut off the plug I thought I’d try the compressor in a different socket, blew the fuse. I tried with an extension cable , blew the fuse.
After about 5 fuses later it stopped blowing fuses & working ok. I spent over an hour of constant use & worked fine?

[minifreek1]

It seems to me theres nowt wrong with the supply wiring, but the fuse blowing indicates a problem with the compressor. Why keep uping the fuse value instead of solving the problem in the first place. If its been fine for months then suddenly not, there's a fault developed. 3kw is acceptable on a 13 three pin plug. 13amp fuse blows constantly, there's a serious problem somewhere.

[Cooperman]

One question is do you have the correct oil in the compressor? Too thick an oil will cause this problem.

[One step at a time]

It seems to me theres nowt wrong with the supply wiring, but the fuse blowing indicates a problem with the compressor. Why keep uping the fuse value instead of solving the problem in the first place. If its been fine for months then suddenly not, there's a fault developed. 3kw is acceptable on a 13 three pin plug. 13amp fuse blows constantly, there's a serious problem somewhere.

A 3 kw Anything will pull 13.04347826086957 Amps. Yes fix the possible fault with the compressor and then you could fit a 20Amp double pole switch with the correct supply.

[JXC Mini GT]

Another factor in the equation is the supply voltage which you have no control over, a supply voltage of 230 v will be as stated above pull 13.0434 Amps, a 220 v supply will pull 13.63 Amps. Supply voltages at peak times are likely to be lower therefore increase in amps drawn.
I would agree that a 20 Amp dedicated supply complete with commando type plug and socket will solve the problem.

[ACDodd]

I run a 3 hp single phase machine of dedicated 16amp type C breaker with no problems even at -4°c cold starts. 13amp plug is always going to be a problem in the cold months.
The biggest problem with most home garages is the input supply to the workshop is usually too small. This means it takes too long for the motor to run up to speed as it can't pull enough amps though the small cable. Change your supply circuit.

Ac

[Raggedroy]

Another factor in the equation is the supply voltage which you have no control over, a supply voltage of 230 v will be as stated above pull 13.0434 Amps, a 220 v supply will pull 13.63 Amps. Supply voltages at peak times are likely to be lower therefore increase in amps drawn.
I would agree that a 20 Amp dedicated supply complete with commando type plug and socket will solve the problem.

I think your calculation is incorrect, you have assumed the 3kw is the constant and does not vary with variations in voltage. Lowering the voltage will actually lower the kw and the current. You could however lower the voltage so much the motor doesn't have enough torque to rotate the compressor pump and stalling the motor, thus resulting in low back EMF and no limit on the current pulled = overload.

 

A motor can pull 5-10 time full load current on startup. it is unlikely a 13A plug top fuse will hold. I would recommend a 16A plug and socket backed up with 16A type C or D MCB. Not forgetting all socket outlets up to 63A should be protected by RCD.

[Raggedroy]

I run a 3 hp single phase machine of dedicated 16amp type C breaker with no problems even at -4°c cold starts. 13amp plug is always going to be a problem in the cold months.
The biggest problem with most home garages is the input supply to the workshop is usually too small. This means it takes too long for the motor to run up to speed as it can't pull enough amps though the small cable. Change your supply circuit.

Ac

 

Fair comment, too smaller supply cable will result in voltage drop, lowering the kw and starting torque.

[JXC Mini GT]

 

Another factor in the equation is the supply voltage which you have no control over, a supply voltage of 230 v will be as stated above pull 13.0434 Amps, a 220 v supply will pull 13.63 Amps. Supply voltages at peak times are likely to be lower therefore increase in amps drawn.
I would agree that a 20 Amp dedicated supply complete with commando type plug and socket will solve the problem.

I think your calculation is incorrect, you have assumed the 3kw is the constant and does not vary with variations in voltage. Lowering the voltage will actually lower the kw and the current. You could however lower the voltage so much the motor doesn't have enough torque to rotate the compressor pump and stalling the motor, thus resulting in low back EMF and no limit on the current pulled = overload.

 

A motor can pull 5-10 time full load current on startup. it is unlikely a 13A plug top fuse will hold. I would recommend a 16A plug and socket backed up with 16A type C or D MCB. Not forgetting all socket outlets up to 63A should be protected by RCD.

 

I used ohms law where power (kw) = voltage x load (amps) when the maximum power stated was 3kw the variants are voltage and current i.e

3000w divided by a voltage of 230V will draw 13.0434 Amps a lower voltage will increase the Amps

[Raggedroy]

Another factor in the equation is the supply voltage which you have no control over, a supply voltage of 230 v will be as stated above pull 13.0434 Amps, a 220 v supply will pull 13.63 Amps. Supply voltages at peak times are likely to be lower therefore increase in amps drawn.
I would agree that a 20 Amp dedicated supply complete with commando type plug and socket will solve the problem.

I think your calculation is incorrect, you have assumed the 3kw is the constant and does not vary with variations in voltage. Lowering the voltage will actually lower the kw and the current. You could however lower the voltage so much the motor doesn't have enough torque to rotate the compressor pump and stalling the motor, thus resulting in low back EMF and no limit on the current pulled = overload.

A motor can pull 5-10 time full load current on startup. it is unlikely a 13A plug top fuse will hold. I would recommend a 16A plug and socket backed up with 16A type C or D MCB. Not forgetting all socket outlets up to 63A should be protected by RCD.

I used ohms law where power (kw) = voltage x load (amps) when the maximum power stated was 3kw the variants are voltage and current i.e
3000w divided by a voltage of 230V will draw 13.0434 Amps a lower voltage will increase the Amps

You have assumed the 3kw is the constant, it is not. The manufacturer would have stated the motor is 3kw on the assumption it is used on 230v. If you lower the voltage the power output will also drop.

[Raggedroy]

Another factor in the equation is the supply voltage which you have no control over, a supply voltage of 230 v will be as stated above pull 13.0434 Amps, a 220 v supply will pull 13.63 Amps. Supply voltages at peak times are likely to be lower therefore increase in amps drawn.
I would agree that a 20 Amp dedicated supply complete with commando type plug and socket will solve the problem.

I think your calculation is incorrect, you have assumed the 3kw is the constant and does not vary with variations in voltage. Lowering the voltage will actually lower the kw and the current. You could however lower the voltage so much the motor doesn't have enough torque to rotate the compressor pump and stalling the motor, thus resulting in low back EMF and no limit on the current pulled = overload.

A motor can pull 5-10 time full load current on startup. it is unlikely a 13A plug top fuse will hold. I would recommend a 16A plug and socket backed up with 16A type C or D MCB. Not forgetting all socket outlets up to 63A should be protected by RCD.

I used ohms law where power (kw) = voltage x load (amps) when the maximum power stated was 3kw the variants are voltage and current i.e
3000w divided by a voltage of 230V will draw 13.0434 Amps a lower voltage will increase the Amps

You have assumed the 3kw is the constant, it is not. The manufacturer would have stated the motor is 3kw on the assumption it is used on 230v. If you lower the voltage the power output will also drop.
The resistance of the motor us the only constant, (well, impedance actually but that is just adding more confusion).
W=VxI, I=W/V
3000kw/230v=13A
V=IxR, R=V/I
230v/13A=17.7ohm

200v/17.7ohm=11.9A
200Vx11.9A=2.2kw

Less power, less current

Edited by Raggedroy, 11 June 2019 - 06:43 PM.

[JXC Mini GT]

All I am saying is that if the maximum load is 3kw that is fixed, the variables are voltage and load (Amps), if the supply voltage drops and the load 3kw stays the same the Amps will increase.

Manufacturers will state the maximum load at a given voltage as below

Technical specification

Air Tank Volume 100 Litres Air Displacement 14.5 cfm Max Working Pressure 116 8 psi/bar Oil/Oil Free Oil Motor (HP) 3.0 HP Input Voltage 230 V Watts 2200 W Wheel Mounted Yes

 

We may have to agree to disagree on this ?

[Raggedroy]

All I am saying is that if the maximum load is 3kw that is fixed, the variables are voltage and load (Amps), if the supply voltage drops and the load 3kw stays the same the Amps will increase.
Manufacturers will state the maximum load at a given voltage as below
Technical specification Air Tank Volume 100 Litres Air Displacement 14.5 cfm Max Working Pressure 116 8 psi/bar Oil/Oil Free Oil Motor (HP) 3.0 HP Input Voltage 230 V Watts 2200 W Wheel Mounted Yes

We may have to agree to disagree on this ?

The power required to rotate the compressor pump will still be the same but the power output of the motor will change if you reduce the voltage. As I stated, you could stall the motor and cause an overload.