Garden Heater Extension Lead Safety

The year 2020 will inevitably be known for three things; COVID-19, the great toilet roll shortage and the explosion in the use of garden heating. 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 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.

Which lead do I need?

Tough Leads supply a range of extension leads for higher current applications. Use the table below to identify which lead is compatible with your plug.

Heater Plug Compatible Lead Guidance

Splash proof single socket, ideal for temporary use - we would not advise that the socket is left outside for weeks on end.

Single socket, more suited to being left outside for longer periods, or for heavy duty/commercial use.

Double socket,  more suited to being left outside for longer periods, or for heavy duty/commercial use.

An extra socket may be useful for connecting LED lights, a sound system or for charging a phone.

Splash proof single socket, suitable for extending heaters which are fitted with a European 2 pin Schuko or CEE7/7 plug.

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 garden heater 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.
  • A range of splash proof and weatherproof sockets are available, to enable safe use outdoors.

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. See our guide Do I need an RCD for further information, and a step by step guide to finding out if the socket you intend to use is RCD protected.

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. In order to comply with the UK Plugs and Socket Regulations, appliances with a European plug sold within the UK must be supplied with an adaptor. Unfortunately the size of adaptor prevents the lid from closing on outside sockets, and they are also prone to over heating.

Our European socket to UK plug adaptor simple resolves the issue. If the supplied cable is too short, then then our European socket to UK 13A plug extension lead provides an extension and adaptor in one. Ensure that the heater is rated at less than 2,900w. Travel or shaver adaptors must never be used.

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. Generally this means that only one heater should be connected to each extension lead. This limit also applies only to Tough Lead extension leads; DIY store leads may have a much lower rating. 

What if the plug or socket become hot or damaged?

If you are at all concerned that the hot tub plug or socket are becoming warm/hot or damaged in any way, stop using it immediately. 

Over time due to the current drawn, the clips holding the fuse inside the plug can become slightly loose. The loose connection generates heat, the heat increases the resistance of the connection, which in turn generates even more heat, until it rises to the point that the plug starts to melt. The picture below shows the classic signs of a loose fuse; the fuse holder itself is melted, and there is a brown mark and/or cracks appearing on the socket due to the heat, mirroring the position of the fuse in the plug.

Following the simple steps within our guide Why does my plug get warm? can help reduce the chance of an issue occurring.

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 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.

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


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.