Washing Machine Repair Fault Finding
Washing Machine Repair Fault Finding
Last Sunday while our Washing Machine was going through its washing cycle, the electrics tripped.
The first thing I tried was to reset the RCD, but it would not reset.
This was because a ‘leakage’ fault between the ‘line’ wire and the earth connection still existed.
So it was time for my fault finding skills to be put into practice.
There are various strategies that can be used to fault find electrical machinery, and I used to teach marine industry trainee electro-technical officers (ETO), how to do this.
The fault that was immediately visible, was that the mains RCD on the house Consumer Unit kept tripping as soon as the power to the machine was turned on.
Therefore the first thing I did was a visual inspection, inside the machine, after removing part of the outer casing (power was of course isolated first).
Carrying out visual inspections of a system is a good first way to proceed with fault finding, though it can be potentially dangerous, if you are unqualified.
The main reason that taking the casing off a washing machine could be potentially dangerous, is the Capacitor.
The capacitor is a component capable of storing electrical charge for a period of time, even after the power supply has been isolated (disconnected).
Therefore a nasty electric shock could result, if the connections were touched.
The results of my visual inspection of the machine components were that everything looked correct.
What I was looking for were any apparent loose connections, that could be causing a short circuit, or any signs of burn marks on components.
Washing machines contain both a heating element, and a Single Phase Induction Motor, which could be causing the short between the Line (live) phase, and Earth.
Two pieces of test equipment are used to test the heater element, and the Induction Motor. These are a Multimeter, and a Insulation Resistance Meter.
Unfortunately despite formally teaching people on a daily basis how to fault find using an Insulation Resistance Meter, I did not have one available.
Therefore armed with only a multimeter, I needed to use the other fault finding tool available, my Brain!
By asking questions of the person who had used the washing machine, before it went wrong, I gained clues as to the possible fault.
The machine had started ok, and run for a few minutes before tripping the electrics.
This clue helped me make an educated guess that the heating element might be at fault.
My reasoning for this ‘guess’ was that the washing machine cycle had already operated the water pump, to fill the machine with water. The Induction Motor that spins the drum had also worked before the fault appeared.
This in my mind at least eliminated the water pump, as it was not being used when the fault happened.
The Induction Motor on inspection did not have any apparent water that had leaked onto its Stator Coils, which might have caused the Insulation Resistance to lower, and hence trip the mains RCD.
Although without carrying an Insulation Resistance check on the Induction Motor, I could not be 100% sure that the Induction Motor was not causing the fault, I was ‘betting’ on the heater element, based on where in the washing cycle the fault occurred.
The first thing to do when testing the heater element, was to be totally sure that there was no electricity going to it.
I learned the importance of electrical safety at an early age (Age 11), when I forgot to turn off the mains supply, when wiring up an old analogue cooker clock, which I had ‘liberated’ from my parents old cooker.
As you can tell, I survived the shock, but still have three small burn scars on my hands, even today.
To ensure the electrical supply was off, I both checked the plug was removed, and also checked it with the multimeter, set to AC voltage.
Checking with a multimeter when the plug is out may sound overkill, but its something I do automatically, as a second check, in case I have forgotten to check the plug.
The two heater element Spade connectors were pulled off with the gentle help of a flat blade Screwdriver, and a Continuity Resistance check was carried out, across the two terminals.
The resistance shown was within the normal range, so would appear ok.
I still however suspected that there was a short inside the element, between the element wire, and the metal end. This would be caused due to internal resistance breakdown.
Without access to an Insulation Resistance (IR) tester I could not test between the two connections, and the elements earthed metal plate.
Therefore I employed another fault finding strategy, which was to test the machine, with the heater element disconnected.
The two connection wires were disconnected, and insulation tape temporarily put on them, to eliminate the risk of the wires shorting to the washing machine casing, or together.
The machine was then powered up, and it ran successfully without tripping the mains RCD.
This had proved that the Induction Motor and Pump were working ok, and that the fault was with the heater element.
A replacement heater element was purchased, and fitted, resulting in a repaired and working machine.