Garden Heater Extension Lead Safety

The year 2020 will inevitably be known for three things; COVID-19, the great toilet roll shortage and the focus on improving our gardens. Outdoor electric heating provides a great opportunity to use our outdoor spaces for longer in the day, and later into the year, particularly given the unpredictability of the Great British weather! 

Electric infrared outdoor heaters can consume a relatively high current over a longer period of time, more than most other appliances that you own. It is therefore really important that they are powered safely.

Understanding the Hazards of Electricity

What is an electric shock?

During an electric shock, electricity flows through the skin and into the body. The effect of the shock depends on the amount of current and the length of time for which it flows, not merely on the voltage. Current of 1mA will create a tiny tingle, but with an increase to 20mA muscles contract and a person cannot let go of an object. Above 20mA may lead to breathing stopping.1

The main risk is electricity flowing through the heart. When current of around 50mA or greater flows through the heart, it stops beating effectively.1 The heart muscle cells start contracting in a random uncoordinated manor, stopping it from pumping. A shock from a defibrillator is required to stun the heart, in the hope that the special cells which normally cause it to beat in an organised way start to work again.

In addition to stopping the heart beating effectively, an electric shock can also cause:

  • Burns to the skin.
  • Stop breathing either through its effect on the part of the brain that controls it, or causing the diaphragm to spasm.
  • Damage to nerves and internal organs.
  • Fractures to bones caused by violent contractions.

Why does the great outdoors present more potential hazards?

Water is the simple answer! The resistance of someone’s skin is one of the most important factors affecting the impact of an electric shock. Dry skin generally has a resistance of between 40,000 -  100,000 ohms.1 This high resistance limits conduction of potentially life-threatening current to deeper, crucial organs like the heart. Skin resistance is significantly reduced to as low as only 1,000 ohms when wet. As electricity can flow much more easily through wet skin, what might otherwise be a minor tissue injury may turn into a life-threatening shock.2

Powering an Outdoor Infrared Heater

Do I need a weatherproof socket?

Where possible, outdoor heaters should be connected directly to an outside socket. If you do not already have a suitably placed outside socket, the safest approach is to ask a Registered Electrician to install one. 

Cheaper outside sockets may save £5-10 at the start, but they are a false economy. They are often prone to UV damage and less than robust (the small grey clips on one type are particularly prone to breaking). Our Hamilton IP66 outdoor single and double sockets are particularly high quality units, which we have used for many years without issue on our EV range of cables.

Why is an RCD so important?

An RCD, or residual current device, is a life-saving device which is designed to prevent you from getting a fatal electric shock if you come into contact with a live wire or current. RCDs offer a level of personal protection that ordinary fuses and circuit-breakers cannot provide.

An RCD constantly monitors the electric current flowing through the live and neutral wire. If a fault occurs and the live and neutral current become unbalanced (e.g. someone has come into contact with a live wire), the current will flow to earth and the RCD will detect this fault and cut the power immediately. The socket outdoor socket must either be wired to a circuit protected by a 30mA RCD or RCBO in the consumer unit, or have an RCD incorporated within the socket itself.

Can I use an extension lead?

It is advisable not to use a standard DIY store extension lead with outdoor heaters, for a number of reasons:

  • Most DIY store extension leads use cable which is not sufficiently large in diameter (normally 1.25mmsq) to handle the relatively high sustained current required.
  • Most are rather long. Think of a cable like a water pipe. If you want high pressure at the end of your 10m garden, you’re not going to achieve it if you use a long hosepipe the size of a drinking straw! The longer the distance, the larger diameter you need to sustain the same flow. This same principle applies to cable.
  • DIY store leads are generally made from PVC or blue ‘arctic’ flex. Despite frequent claims that artic cable is ‘heavy duty’, it is far from it. It is prone to mechanical and UV damage and is not recommended for prolonged use outdoors or below 5°C. It is also easily damaged by heat.
  • The socket may not be weatherproof, or offer only short term protection.

In contrast, the Tough Leads range of single and double outdoor extension leads are truly heavy duty:

  • Constructed from 1.5mmsq H07RN-F rubber cable, which is specifically manufactured for harsh environments and its safety and performance under extreme conditions simply cannot be beaten.
  • The weatherproof socket's IP66 rating means that it remains watertight, even when subject to powerful water jets from any direction. Unlike DIY store extension leads, it can be used for prolonged periods outside
  • The socket can be fixed shut to prevent others from plugging in anything else.

Why do I need to fully uncoil an extension lead?

Extension leads are designed for the cable to be completely unreeled before use. Using a lead which is still coiled, can lead to the build up of heat, with catastrophic results.

How many heaters can I plug into a socket?

Ensure that the total load of the heaters connected to any single socket is less than 2,990w. This limit also applies to Tough Lead extension leads. DIY store leads may have lower ratings.

The heater has a 2 pin European plug, what can I do? 

Due to the demand for outdoor heaters, some are now being supplied with a European plug. To comply with the UK Plugs and Socket Regulations, these must be supplied with an adaptor. The issue is that the adaptor then means that the plug won't allow the lid on the outside socket to close and they are prone to over heating. You can simply plug in our European socket to UK plug adaptor to resolve the issue. Ensure that the heater is rated at less than 2,990w.

How do I know the electricity supply is safe?

As outdoor heaters draw a relatively high current over a prolonged period, it is important that you consider how safe the supply may be:

  • Domestic electrical installations can deteriorate with use and age. It is therefore important that a periodic inspection is carried out every 10 years for an owner-occupied home and every five years for rented properties or HMOs.
  • As sockets age the contacts can loosen, meaning that the contact between the socket and plug pins is not as firm as it should be, which may increase the risk of over heating. We would always recommend using a relatively new branded socket.
  • Carefully check the socket for signs of damage, such as brown marks around the receptacles or cracks.

Checking the 13A plug

Over time due to the current drawn, the clips holding the fuse inside the 13A plug can become slightly loose. A loose connection may generate heat, and in extreme cases can start to melt the plug. It is worth removing the fuse cover and fuse and checking that it fits tightly on an annual basis, or if you are at all concerned about the plug. The picture below shows the classic signs of a loose fuse; the fuse holder itself is melted, and often the first thing to be noticed is a brown mark and sometimes even cracks appearing on the socket due to the heat.

What if the plug or cable become hot or damaged?

If you are at all concerned that the plug or cable are becoming warm/hot or damaged in any way, stop using the heater immediately. Ensure that the unit and electrical installation are checked by a Registered Electrician. 


This information is provided as a general guide only; if in any doubt, consult a Registered Electrician. Please note that Tough Leads cannot recommend the use of an extension lead outside of a manufacturer’s guidance. It is the responsibility of the user to consider the IET Wiring Regulations, manufacturer's guidance, the safety of the supply and any other relevant risks, before deciding whether to use an extension lead for any given application.