What is this?
Seeing a spark when you switch on a socket with a plug already inserted is slightly different from sparking during plug insertion. The spark occurs at the socket switch contacts rather than at the plug pins. Socket switches are mechanical and use metal contacts that can wear over time. When the contacts are worn or dirty, turning the switch on can cause a visible arc as the contacts close under load.
Common causes
- Worn socket switch contacts making poor connection when the switch is operated
- High inrush current from the connected appliance causing the switch contacts to arc
- Switch mechanism loosening, creating a gap that the current must jump across
- Dust or contamination on the switch contacts reducing conductivity
- Socket that has been heavily used with the contacts worn down
- Appliance with a high starting current (motors, compressors, power tools)
Is it dangerous?
A small spark visible through the switch rocker is usually not immediately dangerous — it is the switch contacts arcing briefly as they close. However, if the sparks are large, you hear a loud crack, the switch feels loose or wobbly, or it happens with light loads (phone chargers, lamps), the socket switch is worn and should be replaced. Repeated arcing degrades the contacts further, creating a worsening problem.
Can I fix it myself?
To avoid the spark, try switching the socket on before plugging in the appliance — though this reverses the spark to the plug insertion point. The real solution is to replace the socket if its switch is worn. A competent DIYer can replace a socket with the circuit turned off at the consumer unit, but if you are not confident working with mains wiring, call an electrician.
When to call an electrician
Call an electrician if the sparking is accompanied by any burning smell, heat, or the switch feels loose. Also call if the socket switch is visibly damaged, discoloured, or if it sparks even with very light loads. If you are not confident replacing the socket yourself, an electrician can do it quickly and affordably.
What will an electrician do?
Inspect the socket switch mechanism and internal contacts
Check the terminal connections at the back of the socket
Replace the socket with a new BS 1363 switched socket outlet
Test the circuit to ensure the ring main is intact
Advise on reducing switch arcing (switching on before plugging in, or using unswitched sockets for always-on equipment)
Typical cost
£50 – £120
Single socket replacement is a quick, affordable job. If multiple sockets need replacing, bulk pricing is usually available.
