Helpful video reference. The LEARN ELECTRICS video "BROKEN NEUTRAL – HOW TO FIND IT – HOW TO TEST THE CIRCUIT AND THE VOLTAGE READINGS TO BE EXPECTED" demonstrates the voltage readings you will see at the socket and how to work backwards to find the break. LEARN ELECTRICS publishes detailed technical tutorials on UK domestic electrical testing and fault finding, with a companion website at learnelectrics.com.
1. Understand what a broken neutral does
Under normal conditions, the neutral conductor in a single-phase circuit carries the return current back to the transformer at near 0V. When the neutral breaks, the return path is lost and the circuit behaves unpredictably.
On a simple radial circuit (a single lighting spur, for example) a broken neutral usually means the circuit just stops working. On a ring final circuit, it is more complex: sockets either side of the break can share the remaining neutral path through the ring, causing the neutral voltage at those sockets to rise well above 0V. That rising neutral voltage can cause permanent damage to electronics and creates a real shock hazard.
At the supply head, a broken neutral is a Distribution Network Operator (DNO) matter and must not be approached by anyone other than the network company. That scenario shows as fluctuating voltage across multiple circuits and sometimes a buzzing from the consumer unit. If you see that, call the DNO's emergency line (find it on your bill) and stay away from the installation.
2. Spot the symptoms of a broken neutral
The clues that point to a broken neutral rather than a simple dead circuit include:
- Lights that dim noticeably when a high-load appliance on the same circuit is switched on
- A socket that reads an unusual voltage (say, 80V or 150V) rather than nothing at all
- Appliances running below full speed or at reduced brightness
- Sensitive electronics such as phone chargers or LED drivers behaving strangely on one circuit
- A circuit that was working fine until a socket was moved or replaced
If the circuit is simply dead and reads zero everywhere, a broken neutral is less likely than an open-circuit line or a blown fuse. Work through the simpler possibilities first.
3. Isolate at the consumer unit and verify dead
Switch off the MCB for the affected circuit. If the board has RCBOs rather than separate MCBs and RCDs, operate the relevant RCBO. Post a warning notice or tape the MCB handle in the off position so nobody restores power while you are working.
At the affected socket or ceiling rose, test between line and earth and between neutral and earth with a two-pole voltage tester. Dead on both means the circuit is isolated. Any reading on either means power is present: do not open the accessory until you understand why.
4. Measure voltage to confirm the fault
If the circuit was showing odd voltages before isolation, restore the circuit and take careful measurements at the affected socket (without opening it). Use a meter that reads true RMS AC voltage.
The key reading is neutral-to-earth. On a healthy circuit, neutral-to-earth should be very close to 0V. A broken neutral upstream of the socket causes neutral-to-earth voltage to rise, sometimes to mains level if a load is connected. Note the reading and restore isolation before opening anything.
If the circuit is a ring and only some sockets are affected, the break is somewhere between the last socket that tests normally and the first socket that does not.
5. Test neutral continuity with a multimeter
With the circuit fully isolated and verified dead at every point you plan to open, use a multimeter set to resistance (ohms) or continuity mode to test the neutral conductor from the suspected break point back towards the consumer unit.
To do this properly: disconnect the neutral at the suspected fault point and at the consumer unit, then test between those two disconnected ends. A healthy neutral reads low resistance (a fraction of an ohm per metre of cable). An open circuit or very high reading (megaohms) confirms the break is somewhere in that section.
Narrow the search by testing from a midpoint on the cable run. This is not always practical in a house where cables are buried in walls, but in lofts or under suspended floors you can sometimes reach intermediate connections.
6. Open accessories back towards the source
Starting at the fault point, open each accessible accessory in turn - junction box, ceiling rose, socket back box - and look for a disconnected or loose neutral conductor. The break is usually obvious: a conductor that has backed out of a push-fit terminal, a screw terminal that has come loose, or a damaged cable where it enters a back box.
On older installations with junction boxes above ceiling roses, it is worth checking the junction box connections as a first step before moving systematically back. These boxes are easy to miss behind insulation in lofts.
Once you find a loose terminal, check the conductor end before reconnecting it. If the copper is discoloured, corroded, or the insulation is damaged near the terminal, the conductor should be cut back to clean copper and re-stripped before reconnecting.
When to call us
A broken neutral at an accessible terminal is something a careful homeowner can fix. The test work that leads you to it does require some understanding of how the circuit behaves, and the voltage readings can be confusing the first time. If you are not sure what the meter is telling you, stop and call. A broken neutral that is left unresolved, or incorrectly diagnosed, can damage appliances or create a safety hazard that gets worse over time.
Broken neutral somewhere in your house?
Richard traces broken neutrals, open-circuit connections and intermittent faults across Sandwich and east Kent. Most are found and fixed in a single visit at the £65 first-hour rate.
Contact Richard