If you have a new account but are having problems posting or verifying your account, please email us on [email protected] for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact [email protected]
Please note that it is not permitted to have referral links posted in your signature. Keep these links contained in the appropriate forum. Thank you.

20m Granny Cable

  • 07-07-2022 6:01pm
    Registered Users Posts: 13,020 ✭✭✭✭

    The longest Granny Cable I can see online is 10m. Does anything longer exist?

    Is it safe to plug a reputable 10A 10m granny cable into a heavy duty extension lead to extend the length?


  • Registered Users Posts: 514 ✭✭✭VikingG

    I presume there is no issue as long as you extension lead is rated for the current...

  • Registered Users Posts: 13,020 ✭✭✭✭josip

    Some info online about the granny cable having a temp sensor in the plug, as well as drawing not more than 10A. There are reports/stories of 13A and 16A plugs melting. I was thinking that as soon as I insert an ordinary extension cable, I negate that protection. Would an RCD extension cable compensate somewhat? If it were to go on fire, then it might detect a poor situation :)

  • Registered Users Posts: 321 ✭✭walshtipp

    You are not negating any protection by using an extension lead. But ensure that the extension lead that you use is rated the same or higher than the charger. An RCD extension would make no difference as RCDs do NOT trip on overload. They only trip if current is leaking to earth. There will be a 13A fuse in the extension lead plug which will provide overcurrent protection for the lead.

  • Registered Users Posts: 9,909 ✭✭✭the_amazing_raisin

    The danger of using an extension cable is that the current drawn by the charger will exceed the cable rating

    For example over a 10m distance there will be some losses to resistance in the wire, let's say it was 0.5A

    If the cable is rated for 10A and the charger is pulling 10A then the total current draw with losses is 10.5A. This could exceed the max current of the plug on the extension lead (or the socket) and causing damage

    Best way to avoid damage is to use an extension lead with a higher current rating than needed (13A minimum, ideally 16A) and ensuring the socket you're plugging into is capable of handling a full 13A

    Alternatively if your car has the option of reducing charge current then that's another option to protect against overloading

  • Advertisement
  • Registered Users Posts: 22,455 ✭✭✭✭ted1

    Just about to say that. Never use an extension cable without unwinding it.

  • Moderators, Sports Moderators Posts: 17,883 Mod ✭✭✭✭slave1

    Would you not just go to an electrical supply place locally and get them to spec the cable and length, then just wire it yourself to plug and socket?

  • Registered Users Posts: 11,014 ✭✭✭✭salmocab

    Only a few weeks back I said to a painter that borrowed a lead to unroll it fully so it doesn’t melt. He came back an hour later saying that lead isn’t working. I swear I nearly burst him.

  • Registered Users Posts: 12,657 ✭✭✭✭mfceiling

    I got a special ev crowd in England to make me a 25m cable. It's very heavy and has a waterproof box on the socket end. Think it was about £100.

  • Registered Users Posts: 9,909 ✭✭✭the_amazing_raisin

    Is it safe? Depends, if you want the universally safe answer, no you shouldn't do this, there's an unavoidable risk of causing a fire

    Can you do it safely? Yes in theory, lots of EV owners are doing this without issues so it's definitely possible

    So to expand a bit on what I said about the cable resistance, the granny lead will be setup to draw 10A from the socket

    Putting an extension lead in the middle is basically adding a resistor. For the granny lead to draw 10A means the extension lead is drawing slightly more than 10A from the socket

    Now in theory most sockets in Ireland can handle 13A (just a theory, more on that in a moment). So you'd need to dramatically increase the resistance to cause damage

    However using something like a 50m extension lead could put you close to the limit

    So if you want to play it safe, use the shortest lead to suit your needs and get a high rated cable. Using a higher current rating on the cable means there's less resistance so the extension lead won't increase the amount of current as much

    Using an RCD won't really help you in this respect, they're designed to stop people getting electrocuted. In theory a circuit breaker could help but they're really designed to detect a fault in the circuit so would be rated for several times the operating current

    No the really tricky thing is how much current the socket can handle.

    As I said in theory it should be able to handle 13A. But if it's an old house, or a spur circuit or is badly wired then that mightn't be the case. The socket might be barely able to handle 10A in which case your extension lead will put it over the limit

    And since the circuit breaker in the fuse box is going to be rated for several sockets in parallel, it's not going to help you either

    So you can end up with a lovely fire or melted socket in this case

    In summary, I'd say knowing the setup of the socket you're plugging into is as important as having a good extension lead.

    If in doubt, reduce your charging current of possible or use a different socket. Or charge somewhere else if that's an option

    As much as not having enough charge will ruin your day, a fire will probably ruin it more

  • Advertisement
  • Registered Users Posts: 9,909 ✭✭✭the_amazing_raisin

    List of dangerous assumptions:

    • The person you're speaking to knows what they're doing/talking about
    • The person you're talking to is capable of understanding basic instructions
    • The person is listening to you
    • The person will follow those instructions if they do understand them and did listen
    • They're insured

  • Registered Users Posts: 20,156 ✭✭✭✭ELM327

    I have a granny cable plugged in to a 15 meter extension cable. The cable is 13a rated and outside rated. This is our secondary charger behind a blue 32a CEE plug, until my wall charger gets installed.

    Once the cable is correctly rated and you dont use it when it's wrapped up etc it will be grand

  • Registered Users Posts: 21,197 ✭✭✭✭Alun

    The issues with using an extension cable are indeed partly to do with the rating of the extension cable, yes, but there's another important issue regarding thermal protection.

    The plug on portable EVSE's (granny cables) have a device built into them that measures the temperature in the plug and reduces the current if it gets too hot. The main reasons why this might happen are if the socket that it's plugged into is of poor quality or is worn causing sparking and build up of carbon deposits causing more warming etc. and/or a plug with pins in bad condition or a loose fuse holder.

    In many cases, if this happens it's not a big deal, if the damage to the plug/socket combination isn't too great and the length of time the appliance connected to it is in use is relatively short (kettle, toaster etc.) but for a device like a portable EVSE that could be running at a constant 10A for 4-5 hours it's a different matter.

    So, if you plug your portable EVSE directly into a dodgy socket, you're protected as the thermal protection will kick in and reduce the current.

    If you plug an extension lead into that same dodgy socket, then you're not.

  • Registered Users Posts: 20,156 ✭✭✭✭ELM327

    Or just don't have dodgy sockets?

    I have my two EVs charging on a pretty much standalone circuit that is only connected to 3*32a CEE plugs, a couple of lights, and some sockets, all of which are in my garage. The house is on a different circuit. It's unlikely that there is going to be an issue with temperature or sparking etc as all sockets and the cable are new and in good condition. (The electrical setup predated my purchase of the house but it's a perfect setup).

    There have been times here overnight where one of the 32A CEE plugs and one socket connected to an extension to an EVSE were both in use, drawing a combined 42 amps for 8+ hours.

    I really dislike this notion that is going around that you can't use a granny cable EVSE on a regular basis. You absolutely can. I did it for a year, where I did 60,000 km in a Leaf24 as my only method of home charging. You just have to be not a moron. Check the condition of the plug and socket regularly. I'd do this anyway even on a fitted Rolec.

  • Registered Users Posts: 21,197 ✭✭✭✭Alun

    If youi're confident about the quality of the socket then, yes, the chances of any overheating issues are greatly reduced, but the nature of such devices is that usually you're going to be using them when you're away from home, where you possibly don't have that guarantee. I'd contend that people using portable EVSE's on a more or less permanent basis such as you describe above are in a minority.

    Additionally, prolonged, constant high current draw on even a brand new 13A socket can, over time, degrade it, so if you're going to do that then regular checks are, as you point out, still necessary.

  • Registered Users Posts: 145 ✭✭prosaic

    Some people are talking nonsense.

    If you are drawing 10A at the charger, you are drawing exactly 10A at every point in the circuit (except where something else is also is also drawing current). Current is a constant, except where there is a source or sink of current.

    Adding resistance, in the form of dodgy connections and under-rated or long cables, redistributes the voltage-drop across the circuit. Bigger resistance takes more voltage and dissipates more energy (in heating for connections and cables).

    So if your charger is at the end of poor plugs and wires, you get a lower voltage there as the rest of the voltage is busy making heat and fires.

  • Registered Users Posts: 9,909 ✭✭✭the_amazing_raisin

    I guess for many people they'd be using the granny lead at somewhere like a holiday home or a friend/relatives house.

    It's harder to be certain of the quality of the circuitry there.

    But yes, as a general rule using the granny lead should be fine. There's several cars around me using granny cables exclusively

  • Registered Users Posts: 20,156 ✭✭✭✭ELM327

    I use it everywhere... but always with a note of due diligence. EG my inlaws in wexford before we moved down here, I would charge at one of their newly installed outdoor sockets. There wasnt much else on that circuit.

    However when we stayed in an airbnb that had an external socket in a garage, there was other stuff on the same circuit and the socket was cracked and old looking so I didnt use it and instead relied on public charging for the few weeks.

    Common sense is needed. But there's no inherent risk to using a granny cable. The risk lies elsewhere, eg bad wiring, bad sockets, etc.

  • Registered Users Posts: 2,726 ✭✭✭Type 17

    I've been using a (10A) granny charger with a self-made* 10m extension cable for almost a year now, with no issues whatsoever. It's often charging for 8 hours at a time, and sometimes up to 15 hours. (We're going to get a proper home charger later this year, but it's going to be part of a bigger house-update/upgrade).

    I checked the house socket faceplate that was most convenient to use when I bought the EV, and again after a few months (opened it up, checked for good, tight (but not too tight) wire-connections, checked that the contacts were gripping the plug-pins well, checked that there was no previous overheating, etc).

    I also check the socket and plug temp by touch after every use, and regularly visually check the plug-pins for signs of burning/arcing/overheating.

    There are no issues using a (good-quality, correctly-specc'ed) extension cable, once you keep an eye out for wear/overheating.

    *Here's a post about how I spec'ed it, and how relatively cheap it was -

  • Registered Users Posts: 6,019 ✭✭✭zg3409

    Buy the heaviest extension lead you can get, and ensure the socket is in a waterproof box as often the join us outdoors. Tough leads in UK specialise in this.

    Many /most non manufacturer branded granny cables don't have a temperature sensor in the plug, think eBay, Screwfix versions. Some eBay granny leads are labelled 16 amp and the draw 16 amp through the 13 amp UK plug!. They are extremely dangerous.

    When I first used a granny cable I replaced the socket on the wall with a brand new one, just to be sure. When away from home I check the plug is not warm every 30 minutes. Be sure to stop the car charging before unplugging anything as unplugging when under heavy load will cause sparks and wear the socket. If regularly granny charging at home try not to unplug and replug every day. The generally recommendation is to use cables with "2.5mm squared" wire rather than "1.5mm" wire. Use waterproof sockets in line. Try use manufacturer branded granny cables rather than other brands. If you can get a proper home charger do that. Even a dedicated outdoor waterproof socket is safer than using indoor sockets. Try not to charge when asleep on unknown sockets.

  • Advertisement