Moved compressor won't start

[martlewis]

Hi,

A while ago I had a spark run SWA to a cu in my workshop. The house has a 100A earth leakage trip everything to the outhouse is on a 32A rcd protected circuit.

I recently moved an air compressor from it's old home inside the house, out to the workshop. Now when it starts up the lights im slightly in the workshop and 9 times out of 10 it won't start running. It sounds like it's trying to "turn over"?

I'm sure I read somewhere about air compressors on extension reels that can't draw enough current to start but I'm may have imagined it. Can anyone suggest anything or perhaps there is something that can be installed near the compressor to help with current etc?

Cheers all.

 

[securespark]

perhaps there is something that can be installed near the compressor to help with current etc?

Yup. A larger supply.

Seriously, what is the rating of this equipment? What is different now, electrically speaking, compared to how it was wired before?

 

[bernardgreen]

Did you tell the electrician who put in the power supply thay you would be running a compressor in the workshop ?

It would appear that the cable to the workshop is too small to carry the start up current of the motor and as a result the voltage at the compressor drops too low.

If the electrician knew about the compressor then it was up to him or her to calculate the sixe of cable required for the start up current whic is considerably more than the running current.

 

[plugwash]

how long is the run?

what size is the cable?

is the cable in a duct or burried direct in the ground?

what is the specified startup current of the compressor (which as others say may be much higher than the running current).

unfortunately it seems like the only soloution may be to replace the cable to the workshop with a larger size.

 

[JohnD]

You say you recently moved the compressor, which used to be in the house, to your outbuilding.

So I don't see any scope to blame the electrician for failing to provide adequate cabling to equipment that wasn't in the outbuilding when he did his work.

 

[bernardgreen]

You say you recently moved the compressor, which used to be in the house, to your outbuilding.

So I don't see any scope to blame the electrician for failing to provide adequate cabling to equipment that wasn't in the outbuilding when he did his work.

I wasn't blaming the electrician unless the OP had mentioned about the compressor being moved when the installation was being planned.

One option put the compressor back in the house and run an air line out to the shed with a local air reservoir

 

[ricicle]

Just a thought - is moving the compressor just a coincidence.Is the capacitor failing which will not provide the second phase required for starting a single phase motor, and as the motor is not turning there is not enough back EMF to keep the current down so the motor is drawing starting current all the while and is showing up as a reduction in voltage on the lights?

 

[bernardgreen]

Just a thought - is moving the compressor just a coincidence.Is the capacitor failing which will not provide the second phase required for starting a single phase motor,

Good thought, was the lead on the compressor replaced during the move ? The start capacitor may go to a fourth terminal ( L N E and C ) and need to be strapped to one other terminal. if so then maybe the strap was ommitted when the new lead was fitted. ( been there and got the T shirt )

 

[Belle427]

aye,surely the compressor isnt that big and its down to maybe a dodgy connection somewhere

 

[davy_owen_88]

From another forum I have found out it is only a 1.25HP compressor (5A-ish), on a 4mm^2 feed over 6m so it's unlikely the problem is due to volt drop, unless he's running some other major tool at the same time.

Davy

 

[ricicle]

From another forum I have found out it is only a 1.25HP compressor (5A-ish), on a 4mm^2 feed over 6m so it's unlikely the problem is due to volt drop, unless he's running some other major tool at the same time.

Davy

Yes - but it could be pulling in the region of 50ish amps on locked rotor

 

[davy_owen_88]

Yes - but it could be pulling in the region of 50ish amps on locked rotor

True, but even at 50A:

11mv x 50A x 6m / 1000 = 3.3v - still within acceptable limits (depending on other circuit loading).



Davy

 

[bernardgreen]

Yes - but it could be pulling in the region of 50ish amps on locked rotor

True, but even at 50A:

11mv x 50A x 6m / 1000 = 3.3v - still within acceptable limits (depending on other circuit loading).



Davy

Then add the impedance of the MCBs etc etc between compressor and the incoming main..

 

[ricicle]

I was thinking that the volt drop could be showing up on the whole installation if it is a weak supply thus the lights would dip locally to the shed or in the house regardless of whether the sub main could handle the 50ish amps

 

[JohnD]

I would be interested to know if the compressor works OK when you hump it back to the house and plug in there.

Do you have a socket on your cooker switch?

How long is the flex/extension cable? And how thick?