Compressor Wiring Conundrum

[awemawson]

I took delivery of a Clarke 18CFM single phase compressor today:

Clarke XE18/200 (O/L) 18cfm 200 Litre 4HP Industrial Air Compressor (230V) - Machine Mart

www.machinemart.co.uk

Now the advertising and the (very mimimal) book of words insist that it needs to be fed from a 40 amp supply. This dictates a 3 core 6mm flex from compressor to its socket.
It comes with a tail of flex cable that has an o/d of 9.5 mm and I think being generous is only 4mm so NOT rated at 40 amps.

In preparation I'd obtained some 3 core 6mm butyl flex cable which has an o/d of 14.1 mm. Now admittedly I've not yet dismantled the wiring head but looking at the input gland there is no way it's going to take the 6mm cable and the thinner stuff doesn't comply with their own instructions.

. . . how the heck cane they do this?

 

[Barking Mat]

I took delivery of a Clarke 18CFM single phase compressor today:

Clarke XE18/200 (O/L) 18cfm 200 Litre 4HP Industrial Air Compressor (230V) - Machine Mart

www.machinemart.co.uk

Now the advertising and the (very mimimal) book of words insist that it needs to be fed from a 40 amp supply. This dictates a 3 core 6mm flex from compressor to its socket.
It comes with a tail of flex cable that has an o/d of 9.5 mm and I think being generous is only 4mm so NOT rated at 40 amps.

In preparation I'd obtained some 3 core 6mm butyl flex cable which has an o/d of 14.1 mm. Now admittedly I've not yet dismantled the wiring head but looking at the input gland there is no way it's going to take the 6mm cable and the thinner stuff doesn't comply with their own instructions.

. . . how the heck cane they do this?

40 amps is probably very briefly as the motor starts, leave the original tail, use what you've bought, I'm sure it'll be fine.

 

[roofman]

Being single phase that motor will be a Chinese 4HP i have the same pump on one of my comps and its had an Italian 3HP for the last 10 years running from a 13amp plug.

 

[julianf]

I took delivery of a Clarke 18CFM single phase compressor today:

Clarke XE18/200 (O/L) 18cfm 200 Litre 4HP Industrial Air Compressor (230V) - Machine Mart

www.machinemart.co.uk

Now the advertising and the (very mimimal) book of words insist that it needs to be fed from a 40 amp supply. This dictates a 3 core 6mm flex from compressor to its socket.
It comes with a tail of flex cable that has an o/d of 9.5 mm and I think being generous is only 4mm so NOT rated at 40 amps.

In preparation I'd obtained some 3 core 6mm butyl flex cable which has an o/d of 14.1 mm. Now admittedly I've not yet dismantled the wiring head but looking at the input gland there is no way it's going to take the 6mm cable and the thinner stuff doesn't comply with their own instructions.

. . . how the heck cane they do this?

Ive got that machine... Or at least the same pump and the same reciever. Mine is "airmaster" branded, which, i think, was what machine mart used to sell them as.

But, obviously, the motor could be different. Ultimately, its the plate on the motor that you need to go on, not machine marts website.

I have mine on a 16a plug, comming off a, umm, probably c curve breaker (dedicated), but it may just be a b.

 

[Kram]

40A is the start up current, it would run from a 16A type B or C curve breaker with a 13A plug.

 

[awemawson]

Yes I know it's the start up current that's the issue, but being 'on' 24/7 it may well start up many times in a day when blasting for instance. The fusing needs to protect the cable as well as the machine and a 40 amp C type breaker (C curve for motor starting) doesn't protect the thinner cable hence the conundrum.

 

[julianf]

I dont know the reason why, but belt drives seem to be much easier on start up than direct drive. I assume the belt itself smooths things out a little.

I have the machine i mentioned, and another direct drive. The direct drive is way more bother, even though, on paper, they are similar spec.

I am not concerned about my machine, and, i think, yours will also be fine, assuming its not on the end of a long (volt drop) spur.


ps mine has 2.5mm cable from the compressor to the 16a plug, but, again, the motor on mine is probably different

(i put the 2.5 on it - it came with thinner, iirc, but i was not the original owner)

 

[brightspark]

I took delivery of a Clarke 18CFM single phase compressor today:

Clarke XE18/200 (O/L) 18cfm 200 Litre 4HP Industrial Air Compressor (230V) - Machine Mart

www.machinemart.co.uk

Now the advertising and the (very mimimal) book of words insist that it needs to be fed from a 40 amp supply. This dictates a 3 core 6mm flex from compressor to its socket.
It comes with a tail of flex cable that has an o/d of 9.5 mm and I think being generous is only 4mm so NOT rated at 40 amps.

In preparation I'd obtained some 3 core 6mm butyl flex cable which has an o/d of 14.1 mm. Now admittedly I've not yet dismantled the wiring head but looking at the input gland there is no way it's going to take the 6mm cable and the thinner stuff doesn't comply with their own instructions.

. . . how the heck cane they do this?

Yes I know it's the start up current that's the issue, but being 'on' 24/7 it may well start up many times in a day when blasting for instance. The fusing needs to protect the cable as well as the machine and a 40 amp C type breaker (C curve for motor starting) doesn't protect the thinner cable hence the conundrum.

a short length of 4.0mm wont harm or get hot its only on starting so isnt a continuous load use diversity yea sure in the regs it stated 40 amp should be 6.0mm but this happens on ovens that manafacturers suppy and other appliances . dont bother yourself over it the motors only 3kw fla only starting current is high

 

[Kram]

I dont know the reason why, but belt drives seem to be much easier on start up than direct drive. I assume the belt itself smooths things out a little.

Direct drives are usually rubbish universal type motors, whilst belt drives will usually be proper induction motors. That is the main difference.

 

[Dave-sparks]

. The fusing needs to protect the cable as well as the machine and a 40 amp C type breaker (C curve for motor starting) doesn't protect the thinner cable hence the conundrum.

Yes it needs to protect the cable, but only from fault current as overload protection will be included on the compressor, this part of cable size calculations, and associated regulations, is often overlooked by people not designing circuits for a living.
When the requirement for overload protection can be omitted then a cable which is smaller than what you'd normally expect can be correct for the load

Have you checked the actual current rating of the cable fitted to the compressor?

Also C curve may not be necessary, a B type may well be fine and an assumption of B type may be the reason for the recommendation of 40A.

 

[Dcal]

I was given a 3hp compressor because it fried the motor.
I took it apart and found it had been rewound.
I put a new 3HP motor on it (with thermal overload)
It started fine but when my back was turned, it began to labour (when getting towards full pressure) and fried the new motor. The thermal overload didn't save it.
I thought it was a mechanical issue but couldn't find anything wrong

I put a new 4hp motor on it and a DOL starter set to 13 amps.
It started and ran fine but tripped the DOL.
Further investigation showed it needed 17amps to get to full pressure, so it looks like the wrong motor had been fitted at some time.

While trying to get my head around what was going on I found the draw was about 40 amp starting, 10amp @ 0psi, 12amp @ 50psi, 15amp @100psi and 17amp @ 150psi.
I run it off 4mm cable and don't see any appereciable voltage drop.
It's been fine ever since but I do like having the proper overload protection of the starter.

I'd say 17 or 18 amps will be your max continuous full load.

 

[m_c]

A few metres of 4mm cable will trip a 40A breaker if shorted.
I'd imagine even a few metres of 1.5 cable would trip a 40A breaker.

The manual will over specify things to avoid the manufacturer having to deal with spurious faults, which are ultimately caused by people using an inadequate supply.

 

[awemawson]

@Dcal I'll repeat your measurements when it's wired and plumbed in but ATM it's still on it's pallet awaiting installation. Hope to get some time Friday.

(You can admire it when you collectthe hydrovanes )

 

[bourbon]

We had someone decide he knew better than our spec writers and put one of those on a 13 amp plug. He wasn't best pleased when a warranty claim was refused for a melted plug and a fried motor. (I don't know what he had replaced the fuse with)

 

[Jack_K]

Yes I know it's the start up current that's the issue, but being 'on' 24/7 it may well start up many times in a day when blasting for instance. The fusing needs to protect the cable as well as the machine and a 40 amp C type breaker (C curve for motor starting) doesn't protect the thinner cable hence the conundrum.

It's not a 40a breaker that you require. Have a look at the trip curve and you'll find that a 16a breaker or similar is all that's required.

I was given a 3hp compressor because it fried the motor.
I took it apart and found it had been rewound.
I put a new 3HP motor on it (with thermal overload)
It started fine but when my back was turned, it began to labour (when getting towards full pressure) and fried the new motor. The thermal overload didn't save it.
I thought it was a mechanical issue but couldn't find anything wrong

View attachment 481834

I put a new 4hp motor on it and a DOL starter set to 13 amps.
It started and ran fine but tripped the DOL.
Further investigation showed it needed 17amps to get to full pressure, so it looks like the wrong motor had been fitted at some time.

While trying to get my head around what was going on I found the draw was about 40 amp starting, 10amp @ 0psi, 12amp @ 50psi, 15amp @100psi and 17amp @ 150psi.
I run it off 4mm cable and don't see any appereciable voltage drop.
It's been fine ever since but I do like having the proper overload protection of the starter.

I'd say 17 or 18 amps will be your max continuous full load.


View attachment 481852

View attachment 481851

View attachment 481855

View attachment 481849View attachment 481850

View attachment 481854View attachment 481853

It's likely one of the following issues or a combination of them.
- it's not designed to go to 150psi (likely)
- wrong pulley size fitted
- wrong motor size fitted

 

[Memmeddu]

I'd not even go that big, 2.5mm² would work well enough for general use.
But for demanding applications I'd simply go with 4mm²

 

[dave h 2]

The original cable it was supplied with will have the sqmm printed or moulded on the sheath. This machine is claimed to be assembled in the UK so the cable should be legal.
My 2000 iron14cfm 3hp pump pulls 20A on start and 10A running to 120psi. With an old skool moving coil clamp it's a very quick flick to 20A. No idea why an extra 4cfm needs double the current. No 13A fuses have ever been harmed in it's plug yet.

It's a shame that the pump on yours is now aluminium, the same as the short lived cheap direct drive units.

 

[brightspark]

i clocked my 3hp comp . its running at 12 amps and the starting load is 55 amps

 

[6ply]

My Clarke 3 HP compressor will trip a 16A B type breaker on startup. The compressor is on a dedicated circuit and now runs on a C type breaker. The compressor has a basic contactor and no additional overload protection.

 

[brightspark]

my comps and welder run on a Chinese 13 amp plug and have done for the last 50 years