Helpful video reference. We use Artisan Electrics' tutorial "Fault Finding an Electrical Lighting Circuit - Expert Electricians Top Tips", featuring John, as the video reference for this guide. Artisan Electrics is a Cambridge-based electrical contractor who documents real-world fault finding and installation work, and this walkthrough reflects the systematic method a professional electrician uses on site.
1. Identify what has failed
The first question is scope. Has one light stopped working, or has a whole circuit gone dark? Have all the lights on a circuit failed at the same time, or did it happen gradually?
- One light only: lamp failure, loose connection at that fitting, or a failed LED driver are the most likely causes.
- Several lights on the same switch: the switch, the cable from switch to junction box, or the loop-in at the rose serving those fittings.
- Whole floor or whole house: the MCB or RCD at the consumer unit, or a fault near the supply end of the circuit.
- Flickering on one fitting: most often a loose terminal, a failing LED driver, or a dimmer incompatible with the lamp type.
- Intermittent failures: these are harder to track down and are often a loose terminal that makes contact under one set of conditions and not another.
2. Start at the consumer unit
Open the consumer unit cover (do not touch any conductors: just look). Check whether an MCB has tripped to the middle position or whether an RCD has tripped to off.
If an MCB has tripped, try resetting it with the light switches in the off position and no lamps in the fittings. If it holds, fit new lamps and restore them one at a time. If the MCB trips immediately on reset regardless of what is connected, there is a short circuit or earth fault on the circuit that needs locating before the circuit can be used.
If a whole-floor RCD has tripped and will not stay reset, refer to the fault-finding a tripping RCD guide for the systematic half-and-half method.
3. Check the simplest thing first: the lamp
Before opening any switch plate or ceiling rose, replace the lamp or LED module in the non-working fitting. LED drivers and GU10 lamps do fail, and this costs nothing but a few minutes. Try a known working lamp from a nearby fitting if you do not have a spare to hand.
If the fitting has a separate LED driver (common in downlight installations), the driver can fail without any visible sign. Swap the driver if you have a spare of the same wattage.
4. Isolate the circuit and inspect the switch
Switch the circuit off at the consumer unit. Confirm dead at the switch position with a voltage indicator. Unscrew the switch plate and ease it away from the back box.
Check every terminal. A conductor that has pulled out, a loose screw, or a broken terminal can cause a complete or intermittent failure. Reconnect any loose conductors firmly in the correct terminal and refit the plate. Restore power and test.
If there are scorch marks or a smell of burning inside the box, close it up without reconnecting anything and call an electrician. Scorching is a sign of arcing that can lead to fire.
5. Inspect the ceiling rose or light fitting
With the circuit isolated, unscrew the rose cover and inspect the terminals inside. UK loop-in ceiling roses have three terminal blocks: the loop-in (usually three brown conductors), the switched live (brown conductor from the switch cable, often with red sleeve), and the neutral (blue conductors). Check each terminal is firmly seated.
A grey or green corrosion on copper conductors is common in older rose terminals. Trim back any corroded section to fresh copper before refitting, then reconnect firmly.
If you find a junction box in the ceiling void rather than a loop-in rose, open it with the circuit isolated and check the screw terminals inside the same way. Junction boxes hidden above ceilings are a frequent source of faults on 1960s and 1970s wiring.
6. Test for voltage with the circuit live
If the visual inspection found nothing obvious, you need to test with the circuit live to determine where the supply stops. Restore power at the consumer unit. Do not touch any conductor directly: use only the approved voltage indicator probes.
Test at the switch feed terminal (the incoming conductor from the consumer unit side). If there is no voltage here, the fault lies in the cable between the consumer unit and this switch: that is a cable fault requiring a qualified electrician to locate and repair.
If there is voltage at the switch feed but the fitting still does not work when the switch is operated, test the switched live terminal with the switch on. No voltage here means the switch itself is faulty. Voltage here but no light means the fault lies in the cable from switch to fitting, or in the fitting itself.
7. Work along the circuit methodically
Lighting circuits in UK homes follow a loop-in arrangement: the live, neutral and switch feed run into each ceiling rose in turn. If one rose has a loose or broken loop-in connection, all the fittings beyond it on the circuit will fail. Start at the first fitting on the circuit (usually nearest the consumer unit) and work along. Once you find the fitting where power arrives but does not pass on, you have found the fault.
This process takes time but is methodical. Rushing and connecting things back before you have found the fault leads to confusion about which fitting is which.
When to call us
A fault on a lighting circuit is not always straightforward, particularly in houses with loop-in wiring that has been modified by different trades over the years. Richard offers a callout-and-trace service in Sandwich and east Kent: flat callout rate, and a quoted fix price before work starts once the fault is located.
Need a lighting fault found in Sandwich?
Richard traces electrical faults across east Kent. Callout rate applies, quoted fix before work starts, and a test certificate on completion where required.
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