Fault finding on a socket circuit

faulty socket

Fault finding on a socket circuit

By chris 32 0

Finding a fault on a socket circuit can be a frustrating and difficult task if you don’t know how to diagnose and find the fault.

First start with the symptoms:

  • What’s happened?
    – the circuit breaker or RCD has tripped? or both
  • What happened just before the trip?
    – what was being used?  anything unusual? any water leaks or physical damage to the cables?

Follow these steps first:

  1. Turn off and physically unplug all appliances on the sockets, as you do so look for signs of thermal damage, smoke, burning smells or anything that would suggest a fault with the appliance.
    Also turn off any fused switch connection units that might be feeding a boiler, light spur etc.
  2. With everything off try to turn the circuit breaker or RCD back on, if it stays on then it was likely one of the appliances or fixed units that you unplugged or turned off. If this is the case then each appliance should be tested by a PAT Tester or electrician to determine which appliance was faulty.
  3. If the circuit breaker or RCD still trips then it’s time to call an electrician, if it’s urgent then our emergency electrician service is available in the Bristol and Bath area.


This is how we fault find on a socket circuit.

  1. Investigate all the visible signs and symptoms
  2. Testing the continuity of the ring
  3. Test the insulation resistance between all conductors
  4. Investigate findings, locate fault and repair.
  5. Send minor works certificate

Contact us now if you need our fault finding services

Case Study

In this example you can see thermal damage near the line conductor terminal. The testing showed the continuity of the line conductors in the ring had broken and that there was a short between the line and cpc conductors.

socket fault

Breaking the ring into sections and testing between legs until this socket was found, upon opening, it was clear what had happened. The line cable had broken inside it’s pvc sheath just before the termination and probably would have appeared whole to the uncareful eye when installed. This break started to arc over time and when the home owner who stuck at home in self isolation started to use this circuit more heavily then the fault developed more seriously with serious risk of fire. Luckily the socket design and protective devices did their job well. The line conductor continued to arc and burnt through the PVC sheath and hit the metallic earth plate on the socket outlet, you can see in the photo how it has arc welded it’s way, nearly all the way through the metal earth bar. This contact would have created the Earth fault loop current needed to trip the circuit breaker and the earth fault would have tripped the RCD.

Interestingly there was no signs of thermal damage on the front of the socket outlet and there was no appliance plugged in at the time. This happened as it was on one extreme end of the ring and the break in the line conductor meant move the current went on the other side creating a potential between  the conductor to start the arcing process. This is a great example of useful an arcing detection device would have been.


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