Extension Lead Safety: How to Use Extension Leads Safely

Extension leads are one of the most commonly used electrical products in UK homes — and one of the most commonly misused. Electrical Safety First estimates that misuse of extension leads and multi-plug adaptors contributes to hundreds of house fires every year. Most of these incidents are entirely preventable.

This guide covers everything you need to know about using extension leads safely: how to avoid overloading, when to use surge protection, cable reel safety, and how to know when a lead has reached the end of its life.

Every UK extension lead is rated for a maximum current — typically 13 amps, which equates to roughly 3,120 watts. This is the total load the lead can safely carry across all sockets simultaneously. The key is knowing how many watts your devices draw, and making sure the combined total stays below that limit.

Here's a rough guide to common household appliance wattages:

A kettle on its own already uses nearly the full capacity of a 13A extension lead. Never plug more than one high-wattage appliance — kettles, heaters, hair dryers, or microwaves — into a single extension lead at the same time.

Extension leads work well for low-draw devices used together: a TV, games console, and lamp on the same lead is perfectly safe. It's the combination of high-draw appliances that causes problems.

Plugging one extension lead into another — known as daisy chaining — is against BS 1363 safety guidelines and should never be done. It does not increase the available capacity; it simply multiplies the risk. Each additional lead introduces more potential failure points and makes it harder to keep track of your total load.

If you need more sockets than a single lead provides, the safe solution is a lead with more sockets — not two leads connected together. Our MOMAX OnePlug 6-outlet power strip and 8-outlet power strip both offer multiple sockets on a single 2m lead — no daisy chaining required.

This is one of the most important — and most overlooked — safety rules for extension leads. A cable wound on a reel generates heat as current flows through it. When the cable is coiled, that heat cannot dissipate properly, and the temperature inside the reel can rise to dangerous levels, potentially causing a fire.

Always unwind a cable reel completely before use, regardless of how much cable you actually need. This applies especially when running power tools, heaters, garden equipment, or any high-draw appliance. The few seconds it takes to unwind the full reel could prevent a serious incident.

For low-draw devices — a phone charger or a lamp — the risk is lower, but fully unwinding remains best practice and is the recommendation of electrical safety bodies.

If you regularly need power across a large distance, a heavy-duty reel designed for the job is far safer than a daisy-chained pair of standard leads. Our SMJ 25m heavy-duty extension cable reel and Masterplug 50m extension cable reel are built for prolonged use and designed to handle the loads that standard leads are not.

A standard indoor extension lead must never be used outdoors. UK weather — rain, damp, condensation — creates conditions that can cause water ingress into an unprotected lead, creating a serious electrocution and fire risk.

If you need power in the garden, garage, or on a building site, always use an extension lead or reel with an IP-rated weatherproof housing. IP65 means the sockets are fully dust-tight and protected against water jets — the minimum you should look for in an outdoor lead. Check the product specification before purchasing; if an IP rating isn't stated, assume it's for indoor use only.

Keep outdoor leads away from pooled water, avoid running them under garden hoses or through wet grass, and disconnect them from the mains when not in use.

A surge-protected extension lead contains a component — usually a metal oxide varistor (MOV) — that absorbs sudden spikes in voltage before they can reach your devices. These spikes can be caused by lightning strikes, power outages, or large appliances (like a fridge compressor) switching on and off.

Surge protection matters most for sensitive electronics: computers, monitors, TVs, games consoles, audio equipment, and network hardware. A single power surge can corrupt data or permanently damage components — damage that standard home insurance may not cover if an unprotected lead was in use.

For straightforward use — lamps, phone chargers, kettles — surge protection is less critical. For a home office setup or an entertainment system, it's a worthwhile investment. Look for a lead marked with a joule rating: higher joules means greater surge capacity.

Browse our full extension lead range, including surge-protected models.

Using a multi-plug USB adaptor plugged into an extension lead socket is a common setup — but it also adds another connection point and another potential source of overheating. A cleaner, safer solution is an extension lead with USB ports built directly into the unit.

Our SMJ 4-socket extension lead with 2x USB-A ports (£10.99) and Maplin 4-socket lead with USB-A and USB-C ports (£19.99) combine mains sockets and USB charging in a single unit — no adaptor required.

If you're running a desk with multiple devices, the MOMAX OnePlug 65W GaN power strip (£44.99) offers mains sockets alongside 65W USB-C fast charging — enough to charge a laptop directly from the strip without a separate charger.

Extension leads don't last forever. Inspect yours regularly and replace it immediately if you notice any of the following:

• Discolouration or scorch marks on the plug, sockets, or cable — a sign of overheating
• A warm or hot cable during normal use — cables should not generate noticeable heat
• Cracked, frayed, or damaged insulation anywhere along the cable
• A loose or intermittent connection — devices losing power when the lead is moved
• A plug that doesn't sit firmly in the wall socket

Never attempt to repair a damaged extension lead with tape or temporary fixes. Replace the whole unit — extension leads are inexpensive, and the cost of replacement is negligible compared to the risk of a fire or electric shock.

Different situations call for different leads. Here's a quick guide:

• General home use (TV, lamp, phone charger): A standard 4-socket lead is sufficient. The Maplin 4-socket 13A extension lead (£4.99) covers everyday needs simply and reliably.
• Desk or home office setup: A lead with built-in USB-C and USB-A ports saves adaptor clutter. Try the Maplin 4-socket lead with USB-A/USB-C (£19.99) or the MOMAX 6-outlet power strip (£34.99).
• AV rack or server equipment (IEC devices): The Mercury IEC C14 4-socket extension lead (£9.99) provides 4 IEC sockets for AV amplifiers, rackmount equipment, and professional audio gear.
• Workshop, garage, or garden: Use a proper heavy-duty reel — always fully unwound. The SMJ 25m heavy-duty reel (£29.99) suits most domestic use; the Masterplug 50m reel (£76.99) for larger distances.
• Sensitive electronics (computers, TVs, audio gear): Look for a lead with surge protection — check the product specification for a stated joule rating.

• ✓ Keep total load below 13A (3,120W)
• ✓ Never daisy chain two extension leads together
• ✓ Always fully unwind cable reels before use
• ✓ Use only IP-rated leads outdoors
• ✓ Inspect leads regularly — replace if damaged
• ✗ Never plug high-draw appliances (kettles, heaters, hair dryers) together on one lead
• ✗ Never run leads under carpets or through doorframes where they can be crushed
• ✗ Never attempt to repair a damaged lead with tape

Browse all extension leads and cable reels at Maplin →