Why Flat Twin & Earth Cable Shouldn’t Be Used Outdoors

As a local electrician in Pocklington, I often come across electrical work that hasn’t stood the test of time – and in many cases, it’s down to one simple issue: the wrong cable used in the wrong place.

Take a look at the image above. This is a classic example of why flat PVC twin & earth cable should never be used outside. The cable in this photo was installed to supply outdoor lighting on a south-facing wall. Being constantly exposed to sunlight, the outer PVC insulation has badly degraded. It’s cracked, brittle, and starting to fail – all signs of prolonged UV damage.

But here’s the interesting part: where the metal clip has been prized open, you can see the cable underneath is still in good condition. Why? Because that small section was shielded from the sun. This makes it crystal clear – sunlight is the enemy of standard PVC flat cable when used externally.

This type of cable isn’t poor quality – far from it. It’s a perfectly good, safe and compliant option when used within the fabric of the building – such as inside walls, under floors or in lofts. It was never designed to be mounted externally where it’s exposed to rain, frost, and direct sunlight day after day.

Unfortunately, this kind of installation is all too common. If you take a walk down many streets, especially older housing developments or DIY projects, you’ll start to spot it yourself – discoloured, brittle, cracked cables pinned to brickwork. It’s not just unsightly – it can become unsafe.

A proper, qualified electrician will never use flat twin & earth cable outdoors. For external wiring, we always use cable specifically designed for the job, such as:

Hi-tuff or NYY-J cable, which is UV-resistant and weatherproof

Black flexible cable (black flex), suitable for short external runs to lights or accessories, often in conjunction with a suitable gland or enclosure

Steel-wire armoured (SWA) cable for tougher environments or buried runs

Conduit systems to shield standard cable when needed

If you're unsure about the condition of your outdoor wiring, or you've spotted cracking or brittle cables around your home, it's best to get it checked. What looks like a minor issue today can lead to faults, water ingress, or even safety hazards in future.

At KH Electrical, based here in Pocklington, East Yorkshire, we always ensure the correct cable and materials are used for each situation. Whether it's new outdoor lighting, garden sockets, or a full rewire, you can count on safe, compliant, and tidy installations every time.