Hot Tub Electrical Safety including Extension Leads

The year 2020 will inevitably be known for three things; COVID-19, the great toilet roll shortage and the rush to find an inflatable hot tub! With the exponential increase in hot tub ownership, it is vitally important that the electrical risks are properly understood, to ensure that they can be enjoyed safely by your family.

This advice applies only to inflatable hot tubs fitted with a 13A plug

hot tub extension lead safety

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 water make electricity much more hazardous?

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 Inflatable Hot Tub

Weatherproof Socket

Given the increased risk of mixing electricity and water, it is vital that a hot tub is supplied by a socket which has been tested to ensure that it is wired correctly and is protected by an RCD. If you do not already have a suitably placed outside socket, the safest approach is to ask a Registered Electrician to install one. How much will it cost to fit one? The cost will depend on a range of factors and the only way to determine this is to ask a Registered Electrician for a quote.

When citing a hot tub, it is important to consider the requirements of the IET Wiring Regulations, which include:

  • Even when protected by an RCD, any 13A socket must be cited at least 2m from any swimming pool, hot tub or pond/fountain (Regulation 702.32).
  • The socket must be at least 30cm from the ground (Regulation 702.53).
  • Any socket must be fit for the purpose. As a general guide, for use outside a socket should have a minimum IP rating of IP55 (defined as protected against water jets from any direction - hose pipe).

Whilst cheaper outside sockets may save £10-15 at the start, they are prone to UV damage and often less than robust (the small grey clips on one type are particularly prone to breaking). Our Hamilton IP66 outdoor socket is a particularly high quality unit, complete with 10mA socket. It is one of the few available which closes shut even with the larger 2.5mmsq flex and chunkier style 13A plug found on some hot tub 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. Within the UK, most domestic RCDs have a rating of 30mA, which may prevent a fatal shock, but also avoids constant nuisance tripping. In higher risk applications, a more sensitive 10mA RCD increases the level of protection provided, which is why many hot tubs are fitted with such a unit.

Can I use an extension lead?

Many inflatable hot tub manufacturers recommend against using an extension lead. This is likely to be for a number of reasons:

  • Most DIY store extension leads use cable which is not sufficiently large in diameter (normally 1mmsq or 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 hosepipe the size of a drinking straw! The longer the distance, the larger diameter host 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.
  • The lead may not be protected by an RCD. Even though the hot tub is fitted with an RCD, this only provides protection for the hot tub lead and unit itself – any supply socket must also be protected by an RCD.
  • The socket may not be weatherproof.

Just like the pressure is reduced at the of a long hose pipe, voltage is reduced at the end of any cable. The longer the cable, the greater the reduction in voltage at the end. The smaller the diameter of the cable, the more the voltage reduces with each metre. Using an extension lead with cable which is too small in diameter, or is too long, results in the voltage at the socket end being reduced below an acceptable limit. Known as voltage drop, this is a big issue.

Why? Because as the voltage drops, the hot tub will draw more current to compensate. If this exceeds a certain level, the 13A plug may start to overheat and in extreme cases the plug/fuse holder may start to melt. 13A fuses are unlikely to blow when the current only slightly exceeds a safe level, even over prolonged periods of time. In addition to voltage drop, citing a hot tub further away from the house installation may lead to earthing issues (which are too complicated to go into here!).

If whilst awaiting the installion of a permanent outside socket you do decide to use an extension lead, ensure that it is:

  • Constructed from 1.5mmsq or 2.5mmsq rubber cable (known as H07RN-F) for outside use.
  • Is fitted with an RCD at the plug end.
  • Has a weatherproof socket that remains weatherproof when a plug is inserted, with a minimum IP55 rating.
  • The socket can be fixed shut to prevent others from plugging in anything else (teenagers can sniff out a socket for a USB phone charger from miles away!).
  • Place the extension socket as far away as the hot tub lead allows, but in any case more than 2m.
  • Is the minimum length possible.

Tough Leads supply an extension lead specifically designed for use when there is an increased risk of electric shock e.g. due to a decrease in body resistance. Developed following customer feedback, it is the only weatherproof extension lead available within the UK with a 10mA in-line RCD. It also uses extra thick 2.5mmsq cable and has a robust IP66 rated socket. Click here to view the range.

How do I know the electricity supply is safe?

As inflatable hot tubs 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.
  • Only use either a single socket, or a double socket which has nothing else connected to it.

Checking the 13A plug

Over time due to the current drawn, the clips holding the fuse inside the hot tub cable's 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 is from a hot tub, and 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 hot tub plug or cable are becoming warm/hot or damaged in any way, stop using it immediately. Ensure that the unit and electrical installation are checked by a Registered Electrician. Replacement cables and RCDs are available if the unit isn't under warranty.

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 an inflatable hot tub 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. This is of particular importance in circumstances where there is an increased risk of electric shock.