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I bought a single phase induction motor to build a mortar pump, the motor needs to be operated far from the power source (home construction site).

The motor does not start when connected to mains using a 50 meters cable. It rotates a little bit erraticaly then trips the breaker, this is with no load applied. The starting torque seems to be very very low in this configuration.

The motor starts and runs fine when using a short 2 meters cable, in this configuration the starting torque is enough to turn the rotor of the moineau pump.

Video clips without load:

Technical details

Power source (construction site temporary electrical power)

Breaker panel

I don't think I need a D curve breaker as the motor runs fine with the short cable without triggering the breaker.

Motor

Vevor YL-90L-2

Motor plate

Motor: Electrical connections

Motor: start capacitor

Motor: run capacitor

Motor: wiring diagram

Ca: black capacitor, Cb: blue capacitor

I do not know whether the start capacitor is disconnected with a centrifugal switch or relay but I can hear a click when disconnecting the motor and the shaft comes to a near stop.

Cabling

50 meters of 2.5 mm² solid copper wire. U1000R2V 3X2,5 mm²

The cable is laying bare on the ground in a straight line, it is brand new / not damaged.

Conclusion

What causes the failure with the long cable? How can I solve it?

My guess is that the start capacitor does not have an adequate value when using a long cable which causes very low starting torque but my understanding stops there. I can perform tests and publish the results if it can help.

Edit 1

I tested with a bigger cable:

  • First cable: 2 meters / 2.5 mm²
  • Second cable: 36 meters / 25 mm²
  • Third cable: 12 meters / 2.5 mm²

Same result, motor does not spin by itself and trips the breaker.

enter image description here

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  • \$\begingroup\$ Besides the need for a thicker section of the cable, also watch out for the its inductance. At 50 m it will probably exceed 1 mH, in which case any current caused by the sudden flick of the switch may cause some nasty kickbacks. \$\endgroup\$
    – a concerned citizen
    Commented Apr 1, 2022 at 21:01
  • \$\begingroup\$ What should I do about it? An other puzzling fact is that my 2.2 kW air compressor (dual motor) runs fine with a 50 meters 1.5 mm² cable. \$\endgroup\$
    – Victor Lamoine
    Commented Apr 2, 2022 at 7:56

3 Answers 3

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You need much heavier cable from your source power supply to the motor. There is no other easy solution.

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    \$\begingroup\$ How would an undersized cable cause the breaker to trip? Wouldn't that mean less current? \$\endgroup\$
    – evildemonic
    Commented Mar 31, 2022 at 17:11
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    \$\begingroup\$ Single phase 230V, cos φ = 0.8, 16 Amps, 50 meters, 2.5 mm². Voltage drop: 11.92 Volts ! That's 5.18% this is probably way too much. When the motor is starting it must be close to a 50% voltage drop. I will try to use the 25 mm² for the house over 36 meters and finish the remaining length with a 2.5 mm² wire. It should lead to a 4,25 V drop (1.85%) which is probably good. I will post results when the test is done. \$\endgroup\$
    – Victor Lamoine
    Commented Mar 31, 2022 at 19:42
  • \$\begingroup\$ It does not work better. New setup: 2.5 mm² for 2 meters. 25 mm² for 36 meters. 2.5 mm² for the remaining 12 meters. The motor exhibits the same behavior. If I help it rotating (no load) it spins fine but it does not work with a load \$\endgroup\$
    – Victor Lamoine
    Commented Apr 1, 2022 at 17:32
  • \$\begingroup\$ Estimated voltage drop with the new setup: 4.5 Volts / 1.96%. The voltage drop does not seem to be the only problem. \$\endgroup\$
    – Victor Lamoine
    Commented Apr 1, 2022 at 17:36
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Motors take a large current when starting. This may be several times the running current.

Normally, that surge only lasts a moment, before the current drops to normal.

But if the cable has too high a resistance, then this current causes a voltage drop at the load. If that drop is enough to stop the motor starting properly, then it may not spin up. The current remains high, and the breaker trips.

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I noticed the breaker is an RCD type; GFCI for my fellow Americans; at 50m you may have a long enough cable where ground leakage currents become significant enough to cause nuisance tripping.

I wouldn't think that would be an issue running straight off mains but I'll put this down as something to check. Could you supply mains through a non-RCD breaker?

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