Safely Charging your Electric Vehicle Using a Granny Charger

What are the advantages of using a professionally installed charger?

When purchasing an EV, we would always recommend that you get a professionally installed charging unit outside of your home. This ensures that the supply used has been tested to be safe and will achieve a faster charging time. When not at home, it is best to use a public charging point. Most EV manufacturers recommend that a granny charger is not used as the sole means of charging.

What is a granny charger?

Most electric vehicles (EVs) are supplied with a portable domestic charger designed to charge the vehicle when access to a charging point is not possible. Rather confusingly it is commonly referred to as a 'granny charger', as it is a lead to use when visiting relatives such as your granny!

The granny charger consists of a 13A UK plug, a box containing the charger and a socket which connects to the EV. The connector will either be type 1 or type 2 (see section below for details).

In the UK the charger is limited to draw no more than 10A (2.3kW). This is because whilst a UK 13A plug can supply 13A for short periods of time, it may overheat if that amount of current is drawn for longer periods of time. We recommend checking the tightness of the fuse clips in the plug every 6 months or if the plug appears warm using this guide, to reduce the chance of overheating occurring. 

If your car does not have a granny charger, we supply a range of great units here.

What's the difference between a type 1 and type 2 connector?

There are a number of international standards for EV charging sockets. Within the UK, connectors will be either IEC 62196 type 1 (left) or type 2 (right).

Type 1 - Designed by the Japanese manufacturer Yazaki, the connector has 5 pins. It was predominantly used on vehicles from Asia, and is mainly found on older EVs within the UK e.g. Vauxhall Ampera, Mitsubishi PHEV. It allows single phase charging at 3.7kW-7.4kW AC.  

Type 2 - Designed by the German manufacturer Mennekes, the connector has 7 pins. It was adopted as the EU standard for EVs in 2014 and is therefore the most common EV connector in the UK. It enables single and three phase charging at 3.7kW-7.4kW AC.

When ordering a granny charger it is important to correctly identify charging connector fitted to the EV using the diagram above.

Can I use an extension lead with a granny charger?

Often the lead supplied with a granny charger is not long enough to reach a socket. The question of whether an extension lead should be used, and if so which type is best, is probably one of the most hotly debated issues on on-line forums. In addition, some manufacturers recommend that extension leads are not used to charge EVs. This is likely to be because when using  domestic sockets there is no guarantee of the safety of the supply, including the appropriate RCD and PEN fault protection/earth rod protection which is required for dedicated EV sockets. Also, most extension leads available online and in DIY stores are:

  • Manufactured from cable which is not sufficiently large in diameter (normally 1mmsq or 1.25mmsq) to handle the relatively high sustained 10A 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 you need to sustain the same flow. This principle is the same for electrical cables.
  • Use PVC or blue ‘arctic’ flex, which despite frequent claims that it is ‘heavy duty’, the cable is far from it. It is prone to mechanical and UV damage and is not recommended for use outdoors or below 5°C.

There may be occasions when it is not possible to use a charging station:

  • Whilst waiting for a charging station to be installed.
  • Staying away from home.
  • On holiday in the UK or abroad.

In such situations, it is down to the EV user to consider the manufacturers guidance, the safety of the supply and any other risks, before deciding whether to use an extension lead to extend the charger. Given varying advice from manufacturers and varying risks in a whole myriad of charging scenarios, we cannot make a blanket recommendation that an extension lead should be used.

Tough Leads simply supply high quality extension leads for higher current applications; it is down to the user to determine what applications they are used for. Throughout the website, the term 'compatible' refers to the socket used being compatible with the larger 13A plugs used on EV chargers. It is does not infer compatibility with the EV charger itself. If in any doubt, consult an electrician. Tough Leads therefore cannot accept responsibility for any damage caused as a result of using an extension lead.  

How are Tough Leads different to DIY store extension leads?

All of our extension leads are carefully constructed in our UK workshop from the highest quality and most robust cable and connectors available. Most DIY extension leads either have indoor only sockets, or splashproof covers which will not close shut around the EV granny charger cable because:

  • The body of EV plugs are often larger than an average plug.
  • The thicker cable prevents the socket cover from closing.

To overcome this issue, our leads are the only available in the UK which use a socket which closes shut with all EV plugs. Unlike other extension sockets which are only splashproof (IP44 or IP54 rated) for temporary use outside, our sockets are weatherproof (IP66) for prolonged use outside in all weathers.


The H07RN-F rubber cable is specifically manufactured for harsh environments and its safety and performance under extreme conditions simply cannot be beaten. When combined with heavy duty plugs and sockets, our leads will withstand tough daily use for considerably longer than any other type. H07RN-F rubber cable is perfect for EV charging applications:

  • We only use 1.5mmsq cable, which is suitable for sustained high current applications. As the cable itself is rated at 15A, it can easily handle the max 10A load, even over longer lengths.
  • Extremely flexible, bending to 6 times its overall diameter.
  • Very good mechanical resistance to impact and abrasion, making it ideal for harsh environments on-site.
  • Resistant to accidental exposure to a wide range of chemicals, including most oils and greases.
  • Whist we would never recommend that you submerse an extension lead, it’s good to know that just in case it ends up running through a puddle, it’s actually submersible to a depth of 100m.
  • Retains its flexibility and performance over a wide temperature range from -25 to 60°C.

Does the extension lead need to have an RCD?

Whenever you mix electricity, the great British weather and a metal car, it is absolutely vital to ensure that the entire lead is protected by an RCD. A residual current device (RCD) 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. Further details are provided in this guide.

We are often asked the question of whether an extension should include an RCD and the simple answer is:

Yes if ANY of the following apply:

  • The lead if 20m or longer.
  • The socket that you will use is not RCD protected/you're not sure.
  • You may use the extension in various locations.

No if ALL of the following apply:

  • The lead is 15m or shorter.
  • It will only be used with one socket, which you are sure is RCD protected. Further advice on determining this can be found in this guide.

If an RCD is required, there are two types of unit:

RCD Plug

Instead of a normal 13A plug, the lead has a larger RCD plug, which looks similar to the RCD adaptors you can buy. Whilst being the most cost effective option, it does have a number of limitations:

  • As the unit is not weatherproof, the plug cannot be used outside.
  • The size of the plug means that it will not fit into outside sockets.
  • Due to its size, the plug cannot be used in a socket which has an obstruction above it e.g. a shelf.
  • In-line RCD

    The unit is weatherproof with an IP66 rating. As the unit has a standard 13A plug, it does not have any of the limitations of an RCD plug.

    Why do posts on many on-line forums say that only 2.5mmsq flex should be used?

    The 1.5mmsq vs 2.5mmsq flex debate seems to be the most common one with regards to EV leads on on-line forums, and sadly the most uninformed. For lengths of up to 20m, our advice is that the 1.5mmsq flex used in all of our leads is the best option for the following reasons (apologies for getting rather technical!):

    • BS 1363-1:1995 A4:2012 the British Standard for 13A plugs, specifically states that flex must not exceed 1.5mmsq with the line ‘having nominal conductor cross-sectional areas not exceeding 1.5 mmsq’. Therefore, other than manufacturer fitted moulded plugs, 2.5mmsq flex should not be terminated in a 13A plug.
    • The IET Code of Practice for portable appliance testing allows a safe max length for 1.5mmsq flex without an RCD of 15m, and 30m with an RCD. When PAT testing an extension lead you check for the resistance of the earth- a 15m 1.5mmsq lead would be within the 0.2 ohm limit. Voltage drop on the same lead would be calculated according to the wiring regulations as 5.17v, again well within the limit.
    • The data sheets for 1.5mmsq H07RN-F cable generally state a max current of 15A. If the cable is a sensible length, the manufacturers recommended max current is nowhere near exceeded.
    • 1.5mmsq H07RN-F rubber cables do not degrade over time if used up to the full 13A, as this is well within their safe load limit.
    •  In contrast, 2.5mmsq is more expensive, heavier, and more challenging to manage.

    Can I use a UK granny charger abroad?

    Yes, although standard travel adaptors must never be used with an EV granny charger. Most are only designed to power low current appliances and some often dangerously do not connect the earth pin.

    Our guide to Using UK EV granny chargers in Europe and Scandinavia will provide the support you need to select the correct adaptor from our range of heavy duty EV compatible adaptors. For ease of ordering, our range of adaptors for use in most of Europe are collated here.

    Can a European 2 pin plug granny charger be used in the UK?

    Yes, but only with the appropriate adaptor and if the charge rate can be reduced to 10A.

    How do I know the electricity supply is safe?

    Irrespective of whether an extension lead is used, it is important that you consider how safe the supply may be before plugging in your charger.

    • 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 overheating. We would always recommend charging your EV from a relatively new branded socket, such as one manufactured by MK, Crabtree, Schneider, Hamilton etc. 
    • 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.
    • We would always recommend that the supply is checked using a plug in socket tester. Whilst the unit does not provide the same level of testing or assurance provided by a periodic inspection, it does at least provide a simple check of the supply in order to identify basic problems. The unit simply plugs in, and a row of lights illuminate to confirm that the supply is safe to use e.g. there is an earth connection and the live/neutral are the correct way around.