I am about to buy a compressor and the manufacturer says I can’t use an extension lead. It needs a 16a supply which I have for my planer/thicknesser. The P/T runs through an extension lead of about 2m. Why can I not use an extension lead for the compressor? What about just removing the existing power cable and replacing it with a longer one? Also what is the longest air hose I can use with a compressor before I get power loss etc? It is 3hp/14cfm/150psi. Thank you
Compressor Query?
- Thread starter JAW911
- Start date
Help Support UKworkshop.co.uk:
bourbon
Established Member
That sounds like a Machine Mart air master. The reason that we don't advise using an extension is because of the power surge on start up. At 3hp, you are near to the limit of the plug fuse, any extra load, will result in blowing fuses.
A machine with a 3hp induction motor isn't an appropriate load for a 13A plug.
Some people "get away" with doing this for a little while, others not at all, but the supplier / manufacturer are correct in saying that this should be fed from a 16A circuit or greater. This should have the correct type of circuit breaker to handle the startup current of the motor which could easily reach 100A for a fraction of a second.
If you have the proper supply, then a few feet difference in the length of the cable (or use of a short extension to do the same) is neither here nor there, as long as it is decent heavy duty stuff (2.5mm square cross section area wires).
It's not about "extension cable". It is because a longer cable adds a bit of resistance. The startup current is so high that a little more resistance in the flex reduces the voltage at the motor, the motor then takes longer to speed up, the startup surge is drawn out for longer, and longer means hotter so fuse is more likely to blow or breaker to trip at startup.....
Different motors and the weight of moving parts affects the numbers but not the principle. If your planer thicknesser is also 3hp, then the same applies to that.
And you will always get power loss in an air hose while drawing air. It shows up as a pressure drop at the tool end vs the compressor end. The more airflow you need, the more the pressure drop. Ignore the compressor spec and look at the demand of your most air hungry tool. Pick a hose to suit. There will be lots of tables on the web to help you find the right size. Bigger hose has lower loss but is stiffer and heavier.
Some people "get away" with doing this for a little while, others not at all, but the supplier / manufacturer are correct in saying that this should be fed from a 16A circuit or greater. This should have the correct type of circuit breaker to handle the startup current of the motor which could easily reach 100A for a fraction of a second.
If you have the proper supply, then a few feet difference in the length of the cable (or use of a short extension to do the same) is neither here nor there, as long as it is decent heavy duty stuff (2.5mm square cross section area wires).
It's not about "extension cable". It is because a longer cable adds a bit of resistance. The startup current is so high that a little more resistance in the flex reduces the voltage at the motor, the motor then takes longer to speed up, the startup surge is drawn out for longer, and longer means hotter so fuse is more likely to blow or breaker to trip at startup.....
Different motors and the weight of moving parts affects the numbers but not the principle. If your planer thicknesser is also 3hp, then the same applies to that.
And you will always get power loss in an air hose while drawing air. It shows up as a pressure drop at the tool end vs the compressor end. The more airflow you need, the more the pressure drop. Ignore the compressor spec and look at the demand of your most air hungry tool. Pick a hose to suit. There will be lots of tables on the web to help you find the right size. Bigger hose has lower loss but is stiffer and heavier.
Last edited:
Thank you so much for such a detailed reply. So I need to stick with the power cable as supplied, only use my 16a supply, hope that the fuse is up to the startup-current requirement (which I can get checked) and read up about the correct hose to be used for paint spraying. Sorted. Thanks again.
For a spray gun, chances are that you will be choosing between 8mm and 10mm bore hose. I get away with 6mm on a tiny touch up spray but bigger guns need more air. A thinner hose is more flexible and nicer to use. A regulator and pressure gauge on the gun is nice. This lets you set the compressor high enough to overcome all the losses in the hose plus a bit and then forget about it, adjusting the pressure at the gun to get the atomisation just right.
sometimewoodworker
Established Member
My advice is that if you want to use a longer cable the first thing to do is check the size of the conductors. They are likely to be 1mm or 1.5mm just possibly 2.5mm, if they are not 2.5mm sq then you can easily swap the original for 2.5mm sq and make it a 10m cable, possibly longer.
The reason for not allowing an extension cable is that the vast majority of extensions are 1mm or 1.5mm and may well be copper coated steel or aluminium, these extensions even if copper will have the resistance that @Sideways is talking about.
With the power supply as mentioned the 16A is certainly better as it has capacity beyond the normal 13A. however the 13A is quite capable of supplying the power required. The important point is that the MCB or RCBO has the correct curve for a motor to start so you need (or are best advised) to have a circuit with a type C or K breaker, the majority of circuits use a type B.
The type B allows a 3~5 times inrush current so it’s quite possible that your air compressor will pull enough to trip one on startup
The type C allows a 5~10 times inrush current so is useful for things like motors that usually go over the type B limits
The type K allows a 8~12 times inrush current so is useful particularly useful for motors.
However there are calculations required for the circuit to ensure that you are able to safely change the MCB type so this is a job for a competent electrician and you may need to run a dedicated circuit.
With the longest air hose you can run, this is very dependent on the use you intend. I have used a 50 meter set of extensions to run an air duster, however for my spray setup I run an 8 meter 13mm feed to close to the paint room this has 2 filters on it to try to ensure its clean dry air
then I use a 6mm or 8mm from that to the gun. So far I’ve mainly used water based or oil finishes so the 6mm has been easily capable of supplying the required volume.
I recently got a gun with a 4mm tip to spray household vinyl paint, that may require the 8mm hose. And while I know that going airless is the best for that material I can’t justify spending the £3,000+ for the little use I will get out of it, so I will continue to use an air gun.
I live in a climate that kills the cheaper air hoses in a couple of years so have had to switch to reinforced hoses, the most flexible ones will have double or more the life of the cheap ones.
Last edited:
BarbaraT
Established Member
- Joined
- 18 Oct 2023
- Messages
- 60
- Reaction score
- 49
There is no reason you can't make up a 16amp extension with the blue 16amp connectors on both ends. I made one from a 100m roll of 2.5mm artic flex.
The motor draws about 6 times the starting current of its full load current. If the full load current of the motor is 9.6 amps. The starting current would be about 9.6*6=57.6 amps.
A cable rated for the 16A current connected with the correct 16a blue plugs and sockets would be absolutely fine.
The manufacturer probably refers to standard 13A extension leads which would likely be unsuitable as -
1) The machine requires a 16Amp supply
2) A large number of cheap extension leads are rated and fused at 10 Amps
3) A longer normally coiled extension lead is only rated at its maximum amperage when fully uncoiled, the de-rating factor of a coiled or bunched cable is significant and reduces the current carrying capacity of the cable. The result is a potentially dangerous overheating of the cable.
I cant be certain it still is but from memory the
ABAC PRO A29B 90 CM3 - 3HP 90 LITRE BELT DRIVE AIR COMPRESSOR
was the largest (3HP) compressor which can run of a standard UK 13a three pin socket.EDIT - Added the below !
Looking at the Wolf it is almost identical. The difference appears to be that the ABAC used to be labelled as 14CFM but is now sold as 11CFM - I suspect they are pretty identical in terms of output.
(The ABAC is available in the same 150 Litre configuration)
Last edited:
sometimewoodworker
Established Member
Our family can attest to that, mother would run a smallish 2 bar electric fire to warm the room and she had a rather nice extension cable on a winding reel, one time she wanted more than the single bar on about 2~3 meters from the convenient socket some time later she noticed a smell of hot plastic, everyone was thankful that she noticed it before it got to the flame stage, her 10 meter extension cable was the only a 2 meter one if anyone had been brave or stupid enough to plug it it once it cooled down. She was an extremely intelligent lady who had graduated with a double first from Cambridge just before WWII. We could not understand how this basic electrical safety knowledge had passed her by
