Helpful video reference. John Ward (jwflame) tests a plug-in socket tester thoroughly in "Socket Tester Hack and Experiments", demonstrating what each indicator combination means with real wiring faults rather than just reading the legend. John Ward's channel covers UK electrical practice in detail, using correct UK terminology and BS 7671 colour codes throughout.
1. Choose the right tester for UK sockets
UK domestic sockets are BS 1363 13 A three-pin sockets. You need a tester specifically designed for them -- not a two-pin tester intended for European or American outlets, and not a generic import that may map the pins incorrectly.
Testers widely used by UK electricians include products from Socket & See, Kewtech, DiLog, and MK. The Socket & See ST1 is a common sight on a domestic electrician's tool roll: compact, clearly labelled, and made for UK circuits. These are all available from electrical wholesalers and online retailers for under £20.
Avoid very cheap testers with no brand markings or without the CE or UKCA mark. The indicator legend on the tester must be clear and in English so you can cross-reference fault patterns correctly.
2. Check the indicator legend before you start
Every socket tester has a legend -- usually printed on the back -- that maps each combination of indicator lights to a wiring condition. Spend a minute reading it before you plug into the first socket. The pattern for a correctly wired socket varies slightly between brands: some show two amber lights, some show orange-green, and some use numbers or letters. Know what "correct" looks like on your specific tester before you start comparing results.
The standard fault conditions a UK socket tester can detect are:
- Correct wiring. Live to live pin, neutral to neutral pin, earth to earth pin, correct polarity.
- No earth. The earth connection is absent or broken. Common in older properties with unmodernised wiring.
- Live and neutral reversed. The brown and blue conductors have been swapped. An appliance may still work, but the switch in the plug interrupts the neutral rather than the live -- leaving the appliance energised when it appears to be off.
- Live and earth reversed. The most dangerous fault. The earth pin is at mains potential. Anyone touching an earthed appliance casing could receive a shock. Stop using the circuit immediately.
- Open live. No live voltage present. The socket is dead.
- Open neutral. Neutral conductor is broken or disconnected. The socket may appear live with some loads but will not work correctly with others.
3. Plug in and read the lights
Push the tester firmly into the socket until it is fully seated. The indicator lights illuminate within a second or two. If the socket is completely dead -- open live -- no lights will come on at all.
Read the pattern, then check it against the legend. Take note of which socket you are testing as you go so you can find any faults again later.
4. Understand what each fault indication means
Correct wiring: no action needed. The socket is wired to the right polarity with an earth present.
No earth: the socket should be taken out of service and an electrician called. In older properties without an earth conductor, a rewire or at least an RCD socket fitted in place of the standard socket is needed. Using unearthed metal-bodied appliances on an unearthed socket is a shock risk.
Live/neutral reversed: call an electrician. This is a wiring fault at the socket or at a junction earlier in the circuit. It is a Part P notifiable repair in most cases.
Live/earth reversed: stop using the circuit immediately and call an electrician. This means the earth conductor is connected to the live terminal somewhere in the circuit. Every metal appliance casing on that circuit is potentially live. This is a C1 fault on an EICR -- an immediate danger to life.
Open live or open neutral: the socket is not supplying power correctly. Check the consumer unit for a tripped breaker before calling an electrician, but do not assume a tripped breaker is the only cause.
5. Test every socket in the room
Move systematically around the room, testing each socket position. On a ring circuit, a wiring fault at one socket often appears at all sockets on that ring, but not always -- a fault at a junction before the ring splits could affect only part of the circuit. Test them all and note which ones show any indication other than correct.
If you are checking a recently purchased property, do every room including the garage, outbuildings, and any outdoor sockets. Outdoor sockets and those in unheated spaces are the ones most likely to have deteriorated connections.
6. Know the limits of the tester
A socket tester gives useful information quickly, but it cannot detect everything. It will not find:
- A high-resistance earth connection that passes a continuity check but would not carry fault current safely.
- Insulation breakdown that is not yet causing a measurable fault.
- A broken ring that has been inadvertently bridged back to show correct polarity.
- An RCD that is present but has failed to operate within the required time.
For a complete picture of your installation's condition you need a full Electrical Installation Condition Report (EICR) carried out by a qualified electrician with proper test equipment. A socket tester is a useful first check, not a substitute.
When to call us
Richard is available for socket fault investigation and repair across Sandwich and east Kent. A socket tester reading that worries you is a good reason to call rather than carry on using the circuit. Small fault-finding jobs in Sandwich are charged at the £10 per 10-minute local rate.
Socket fault in Sandwich or east Kent?
Richard can investigate and repair socket wiring faults on small local jobs, with correct certification on completion.
Contact Richard