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  1. #1
    Join Date
    Oct 2007
    Location
    Tasmania
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    132

    Default Thicknesser power cable

    I have just purchased a second hand 15" carbatec thicknesser. The cable on the machine was way too short and I have replaced it with a lead from a 15amp extension cord .
    What i didn't think about until after was the cable size. The extension lead cable is 3 core 1.5mm.
    What cable size should a 3hp machine have? Should this be heavier than 1.5mm?

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  3. #2
    Join Date
    May 2009
    Location
    NSW
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    489

    Default

    It all depends on the length of the cable. If you can plug the machine into a nearby power point, say 2M away then your 1.5(square?)mm cable is fine. If you want to run a 10M extension lead then things get tricky. That motor will draw something like 10 amps running but it's starting current will be way higher. Our "rule of thumb" used to be a minimum of 5 times the run current at startup, way more than that if there was a load on the motor at start-up. For me, a 15 amp rated cable would be an absolute minimum and the run would have to be short. The motor would have to have no load on it at start-up. An interesting test is to have a 60W globe connected across the mains terminals on the motor and watch how it dims when you switch the motor on. Plugged directly into a power point the dimming isn't too bad but put a long lead into the circuit and things really get bad. The surge lasts only a fraction of a second (until the motor gets up to speed) but low voltage means the motor takes longer to get up to speed and the current draw is higher for longer. Eventually something has to "give". Sometimes it's the fuse, sometimes it's the motor.

  4. #3
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    As old hilly says length and cross section of the extension is the key.

    The start up current, and "length of time" the start up currents lasts also depends if the motor starts under high or low load.
    Machines like dust extractors, compressors and welders start under higher load so they will have higher and longer start up currents than Table saws and thicknessers .

    My TS and DC both have 3HP motors and I have done extensive testing to see what length and cross section of extension cords do what..

    The TS uses an under floor 5m long x 1.5mm^2 extension cord
    When the TS switch is off, the V at the saw is typically 240V, and when it's turned on the V drops by 2-3V.
    The typical start up current profile I see (each reading is 1/2 sec apart) is; 20, 25, 10, 6, 4 Amps which is its normal free running current.

    The DC has a ~5m long x 2.5mm^2 extension cord - this machine has a V/A meter permanently wired into its switch box as it is very instructive to see what happens as things associated with the DC change.
    The start up current (again about 1/2s apart) is typically 50, 60, 30, 20, 10, 9 Amps (normal running current) which is to be expected as it had a higher starting load than the TS.
    When the DC switch is off, the V at the DC is typically 240V when it's turned on the V drops 3-4V reflecting the higher load. With DCs, the less air going through them lower their current and high the V.

    My welder and plasma cutter (both 15A machines) are ~8m from my nearest 15A point and for those I use a 10m long 2.5mm^2 cable.

  5. #4
    Join Date
    Oct 2007
    Location
    Tasmania
    Posts
    132

    Default

    Thanks guys for replies. As you mentioned Old Hilly if the cable is not right 'something has gotta give' I just didn't want it to be the motor.

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