Tripping Resdual Current Device Fault Finding.

Have you ever had a residual current device in your house that trips and you cant find the fault?

Picture of an residual current device or earth leakage unit as known in South Africa.

 
It is always best to understand the basics on how this unit works to assist you in trying solve the problem before calling an electritian.

There is a toroidal transformer which measures the magnetic field inside the unit, which  is linked to an electronic circuit. Both conductors pass through the transformer as indicated in the drawing below. Under normal conditions the magnetic field, generated by the current passing through the transformer is cancelled as they are flowing in opposite directions.

This unit is able to detect when there is an imbalance in the current flowing through it.

 However when current is carried through to ground, via yourself or for any other reason, an imbalance is caused. This imbalance is detected by the transformer which triggers the electronic circuit.

The electronic circuit, which is calibrated to react when a difference of more than 0.03 amps is detected, activates a electrical actuator which then isolates the unit from the main supply.

A current of more than 0.03 amps and some times even less passing through a person can cause ventricular fibrillation, which can lead to death. However the shorter the period of exposure, the lesser the risk.

Some units also have incorporated over current protection units. This means that you might be drawing too much current, which could also cause nuisance tripping without having a ground fault.

Tests one can do before calling an electrician.

1. Unplug all appliances and reset the RCD unit. If the unit does not trip again, suspect an overloaded unit or an appliance fault.
2. If the unit stays on, plug in the appliances one by one until the unit trips again. If the unit trips again when plugging in an appliance, suspect that as the faulty one immediately. Some times this tripping can also be caused by an intermittent fault on appliance. One will have to be patient in trying find the appliance if it has an intermittent fault.
3. If the unit trips again with all the appliances unplugged, set all circuit breakers into the off position. Note that the main supply must be left on with this test.
4. If the unit trips again, suspect a fault between the neutral conductor (black wire) and ground (green and yellow wire) or a faulty RCD unit.

At this stage it is best to call an electrician. However, should you feel you are a hands on type of person and feel you want to diagnose further, this is what you need to do. However please note that you do so at your own risk. I accept no responsibility for your safety whatsoever. As I have stated earlier it can take less than 0.03 amps to kill you!

1. Switch off the main switch. Open your distribution box.
2. Count your number of wires coming in to your RCD unit. There must only be a maximum of two. Do not do this test if there is more than two wires as you then have a three phase installation. Doing this test will cause damage to your appliances.
3. From the load side of your RCD ( the bottom) disconnect the black wire. Tape it up with insulation tape to make it safe. Replace your cover. Set all trip switches, RCD unit and main power to the on position. If the unit trips again your RCD unit is faulty. If the unit remains on you have a neutral to earth fault.
4. If the unit remained on, switch of the main power and remove the cover again. Remove the tape and reconnect the black wire. Ensure that the terminal is tight.
5. Follow the wire till you reach the other end. This wire should lead to a bar where all the other black wires connect to. This is called the neutral bar. Disconnect the wires one by one repeating exactly the same procedure as you did in step 3. Obviously you will not remove the wire from the RCD unit this time. When you reach the wire that stops causing the unit to trip, you have found the faulty circuit. Leave this wire disconnected and taped up, close up and switch on everything. Check around to see what is not working. Remember this could take quite a while as it could be your hot water cylinder that is faulty. This could take a few hours to find out.
6. Once you have traced your faulty circuit, call your electrician and explain the fault.

Note, that working with electricity is extremely dangerous. You must always Isolate your distribution board before attempting any work. You must close the board before switching on. Never ever disconnect green wires and operate your distribution board like this. The green wire is a wire that ensures the protection and safety to yourself and other users.