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Read the product marking
Look on the back or underside of an extension lead. For a cable reel, check the label for its maximum current when wound and when fully unwound.
Langstane electrical safety guide
Are you overloading your sockets?
Four sockets on an extension lead do not automatically mean four appliances can be used safely at the same time.
Use the calculator to check the combined load, then follow our practical advice for safer extension-lead use at work or at home.
Use the socket calculator
Add your appliances
Socket overload calculator
Select the appliances you intend to use together. The calculator will indicate whether their estimated combined demand could overload a single socket or extension lead.
Test an appliance combination
Appliance ratings are indicative. Check the rating plate or
manufacturer’s information for your actual equipment.
Calculator source
This interactive tool is provided by Electrical Safety First. It
offers general information and guidance; use the marked ratings on
your own appliances and extension lead when making safety decisions.
Know the limit before use
Check the extension lead’s rating
The current rating tells you the maximum load the lead is designed to carry safely.
Do not assume it is 13A
Many extension leads are rated at 13A, but older products, lighter-duty leads and cable reels may be rated at 10A or less.
Check the actual appliances
Use the wattage or current shown on each appliance rating plate. Equipment of the same general type can have very different power requirements.
Reduce heat and fire risk
Use extension leads safely
A suitable product can still become unsafe when it is overloaded, damaged or used incorrectly.
One wall socket
Use only one extension device
Never plug one extension lead into another. Daisy chaining increases the risk of overloading the wall socket and the first extension lead.
Cable reels
Follow both marked ratings
A wound reel may carry much less current because heat cannot escape easily. Fully unwind it when required and make sure it has a thermal cut-out.
Positioning
Keep leads visible and protected
Do not trap cables under furniture, rugs or doors. Keep them away from water, heat and walkways where they could be crushed or create a trip hazard.
Long-term solution
If you regularly depend on extension leads, consider having
additional fixed sockets installed by a registered electrician.
Do not ignore these warnings
Signs of overheating or damage
Stop using the extension lead or appliance if you notice heat, burning, damage or unusual operation.
Heat, smells or visible damage
Look for hot plugs or sockets, a smell of hot plastic or burning, melted plastic, scorch marks, cracks or discolouration.
Damaged cables
Replace leads that are cut, crushed, frayed or repaired with tape, or where coloured inner wires are visible.
Sparks, smoke or noise
Sparking, smoke, buzzing or crackling can indicate a serious fault. Switch off safely and disconnect the equipment if it is safe to do so.
Repeated loss of power
Fuses blowing or circuit breakers operating without an obvious reason can indicate a fault or overload that needs investigation.
Stop using damaged or overheating equipment
Do not keep resetting a breaker or replacing a fuse without finding and correcting the cause. Seek advice from the retailer, manufacturer, a qualified repair technician or a registered electrician as appropriate.
Choose a suitable product
What to look for when buying an extension lead
Match the lead to the equipment, environment and length you need—without creating unnecessary cable or socket capacity.
Buy from a reputable supplier
Choose a properly marked product with a standard UK three-pin plug and appropriate fuse.
Prefer a multi-way bar
A bar-style extension lead generally places less mechanical strain on the wall socket than a block adaptor.
Choose only the length needed
Avoid trailing surplus cable. For reels, select a model with a thermal cut-out and follow its wound and unwound ratings.
Need more reach or extra sockets?
Choose a suitable mains extension lead
Browse extension leads for workplace and everyday electrical equipment, then check the product rating before use.
Langstane Advice & Guides · Socket overload calculator
