Can you ever safely plug and extension lead into an extension lead?
Posted by Kairismummy@reddit | AskUK | View on Reddit | 56 comments
Our new metal strimmer doesn’t reach the end of the garden. I’m using a 15m extension cable and recon I need about 25-30m instead.
My mum and step dad both assured me that it was safe enough to plug another extension cable into the first to reach the end. But I’m sure I’ve read that you should never chain extension cables.
Is it safe to chain them or is do I need to spend another £40 on a long enough cable? It’s the only item that would be plugged in, but it does apparently need a heavy duty cable due to high power.
DaddyJ2874@reddit
Perfectly fine to plug two together, especially for only one item for a limited time 👍
JakeRiddoch@reddit
Mostly it's safe, but depends on what you're doing. The two problems are
Too many things plugged into one socket. This was a bigger issue when most domestic appliances were high draw items - heaters, irons, kettles, toasters. I've seen extensions trip with two portable ovens plugged in; thankfully the fuses tripped/blew rather than cause a fire hazard. I will add that I wasn't the one who plugged them in... Conversely, 6 way extensions with low power items (phone charger, computer monitor, laptop etc) have been fine. You just need to keep the total ampage under 13A.
Second issue is resistance. Two long extensions daisy chained can put up a decent amount of resistance/power loss leading to either heat issues or low power at the far end.
In your specific case, Google suggests power draw under 700W (that's about 3 amps) which would be safe enough unless you have really shitty extension leads. Longer term, I'd suggest keeping an eye out for a 30m (or more) extension lead as they're handy to have around.
mechsman@reddit
You can absolutely chain for single socket use, just make sure you fully unroll/uncoil each lead, especially with a high load like a strimmer. It's to do with the probability of overload with a whole bunch of sockets hanging off one plug. As long as you are aware of the total load on the first plug it's generally fine. Stay under 10A (about 2.4kw) continuous load for a standard plug.
propostor@reddit
Yes you can.
The "multiple extensions" thing is really only a danger if you're using multiple mutlisockets to overload a single mains socket.
But to simply extend a single socket connection, no additional danger beyond the usually basic safety stuff.
Dominionix@reddit
Holy fuck this. Keep trying to explain this to my wife who loses her shit when I plug two together. “You’re not allowed to plug them together, it’s not safe!”
It doesn’t matter if I use 50 of them in a row if there’s still only one thing plugged in at the other end. It matters if I plug 3 of them together and then put a washing machine and tumble dryer into each one of them.
Essentially it comes down to power draw. It doesn’t even matter if you put three of them together and plug stuff into each one if the things you’re plugging in have a low power draw. Just need to be conscious that everything you plug in is coming through a single socket, so if their combined peak draw would be too much for a socket then don’t do it.
RecentTwo544@reddit
Yep, get fed up of explaining this too.
Five extension leads chained together with say, ten low power phone chargers, probably fine.
Two chained together with a fridge freezer, a washing machine, a dishwasher, two air fryers - call the fire brigade.
hotterthanyou2@reddit
Probably add 2/5 heaters aswell
propostor@reddit
If you extend it very very long you'll lose power due to resistance in the wire, but even then it sounds more like a nuisance than a danger.
InternationalRide5@reddit
It can be a danger as the higher resistance lowers the fault current, so the RCD may not trip within the 40 ms at 150 mA or 300 ms at 30 mA.
That's especially important for things like garden equipment if you cut through the cable and are holding the live end.
Dominionix@reddit
Agreed but that's true of any significant length of wire, even single-gang extension leads.
ARobertNotABob@reddit
It's also why when building a house extension, you ensure the extension is brought into the ring main, not "done cheap" as a spur.
zennettac@reddit
On the other hand I'd prefer an over abundance of caution rather than some of the reckless stuff you see in the wild sometimes.
Adversement@reddit
Not quite only danger.
There is another risk, for way too long chain of extension cords: For suitable failures of the load at the end of such a chain, your short circuit current might not be able to trip the circuit breaker at expected rates, or even burn the 13 A fuse in any of the extension cords.
And, then of course much more relevant risk of bringing the short interior extension cords out to the lawn, and getting them wet.
But, yes, the main risk is overloading the circuit. This is even more so a problem in almost any country not UK, where the plugs don't have a fuse, and yet they can sell extension cords with less capacity than the largest allowed mains breaker. That makes already one extension cord sketchy, and a chain a real fire risk even if you wouldn't put in any of the obvious high current devices.
kitch793@reddit
I would like to counter that I have seen this happen once, the socket wasn't overloaded but there was maybe 4-5 extension leads daisy chained to power a PPE Vending Machine ordered by H&S (yes the irony is right there). One of the extensions in the middle melted, not full fire but definitely could have been.
All this to say that yes whilst it is rare and unlikely it can happen. Plus if this is being used for outdoor use I would make sure that you are using one rated for this to prevent moisture ingress, also if you can use one with individually fused outlets and make sure they're all off other than the one in use.
Educational_You_6835@reddit
Years ago I did electrical safety at work and they wouldn’t allow it even if you were correctly calculating the load. The reason was that in an office if you are plugging an extension into an extension then it was probable you were also running it across a corridor or aisle and so creating a trip hazard. On that basis they didn’t consider it safe no matter what.
In reality it’s fine as long as you know what you are doing.
New_Line4049@reddit
Yes. But be mindful of current draw, most extension leads have multiple sockets. People see open sockets and use them, and you end up with way too much stuff drawing way too much current from one wall socket. Also note the extension leads you can coil up in a reel have a lower max current rating reeled up than unreeled, so be sure to fully unwind even if you dont need the full length, or obey the lower limit.
HirsuteHacker@reddit
Don't overload it. Be mindful of how much power everything plugged in will draw. That's the only real risk with daisychaining - you suddenly have a lot more sockets to plug more things in and draw more power.
Daisychaining just for extra wire length is fine.
Inappropriateout@reddit
You can……no problem.
But seriously- get a decent clip on battery strimmer when you replace.
I have Bosch strimmer, 2x hedge cutter ( long reach and normal ) , drills ……and they all take the same batteriies so I have a couple of 4ah battery packs I use for all
It’s so much easier that f’ing around with extensions
Dreadheaddanski@reddit
As long as your not turning a 4 plug into a 16 plug you'll be fine
Polryn@reddit
Wait.wut.... are we not supposed to do that ?
erroneousbosh@reddit
Yes, of course you can.
The problem with daisy-chaining extension leads is not that you've plugged a plug into a socket. The problem is if you plug lots of things into the other socket.
You know how we call them a "Thirteen Amp Plug"? That's because they're rated for a maximum of 13 amps. There's a fuse in the plug that will blow if that's exceeded, and the wiring and plug and socket pins are rated to carry that much current safely (actually, about twice that, giving you some headroom).
If you get a 4-way extension lead and plug it in, you can't plug four kettles into it. Each kettle would draw pretty much the full current available, and the fuse would blow. This wouldn't be safe.
If you plug ten 4-way extension leads into each other and then plug a kettle into the far end, you run a bit of a risk of one of the plugs being a bit damaged or just a bit shit, not making good contact, and overheating. This isn't safe either.
If you've got a pair of 15 metre extension leads, and you plug one into the other and then your strimmer into the far end, it's going to pull maybe 1/3 as much as the kettle - the very biggest electric strimmer I've seen is 1kW. That'll be about 4 amps, well within the rating of the cables.
One thing to watch though is that the cables might not be rated for 13A - they may have a lower rating, especially if the cable is quite thin. Pay attention to the label.
Also, if the extension leads are the ones on a little drum that coils up, don't use them coiled up with heavy loads because the wire will warm up in use and if it's coiled up the heat won't be able to dissipate.
Frankly though if your garden is 30m long you'd be better getting a petrol or battery strimmer.
konwiddak@reddit
I have a theory that this advice started in America where a plug is only good for about 1500W. Much easier to overload a socket in that scenario. A single device into the end of a chain is fine. The worst that will happen is the voltage drop will be significant and the strimmer will be a bit underpowered.
therealhairykrishna@reddit
They also don't have fuses in their plugs. There's no way to pull 20A through a UK extension for any length of time
LazyEmu5073@reddit
A 13A fuse will pass 20 amps indefinitely...
https://www.pat-testing-training.net/articles/images/bs1362-fuse-characteristics.png
GordonLivingstone@reddit
That's a good point. I hadn't realised that plug top fuses would run so long at more than 13A.
In practice, a 13A rated cable will likely carry 20A without serious overheating.
The cables are rated on the basis of a high ambient temperature and various assumptions about how they will be used. A cable stretched out in the open at a normal room temperature will carry more than its nominal rating.
It will also take time to heat up, so will need to be overloaded for a long time before damage happens. Plugging a couple of electric cars in to a four-in-line extension to charge overnight would be a bad idea.
If a long cable is coiled up and stuffed in a warm cupboard then there will be trouble.
So, without actual looking up all the specs, I would think that you are unlikely to set an extension lead on fire by overloading unless you try quite hard.
therealhairykrishna@reddit
Ok, 25 amps
yolo_snail@reddit
Chaining extension leads itself isn't bad, it's when you overload them that you have issues.
There's also the fact that shorter extensions use thinner cables, so if you plugged in 2 15m extensions, instead of it safely being able to support the full 3kW, it might only be able to do 2kW.
For a relatively low load like a strimmer, I'd have no concerns putting 2 leads together.
Greedy-Nature-826@reddit
It's also about voltage drop over the distance.
The extn should be using the correct size of cable to cover current and voltage drop over the length sold.
If two are connected together, the longer distance could have needed a larger cable.
jaa101@reddit
But voltage drop is proportional to power draw (given the fixed mains voltage). Given that a trimmer is only around 500 W, but the extension lead is probably rated to 3000 W, chaining two extension leads will be okay.
Altruistic_Cress_700@reddit
My main point was really that there's nothing unsafe about chaining a hundred extension leads to reach ten miles. So long as they have the right ratings. But the longer they are, the less you'll get out at the end.
Altruistic_Cress_700@reddit
In the OPs case, a strimmer will use a few hundred watts max.
So little danger of overheating the cable. But to be safe unwind it all.
Ultimately, thicker cable (more strands) less voltage drop per unit distance.
You could have 100m of extension leads all daisy chained. But you'll just get heat loss and the related voltage drop. So the strimmer will just turn more slowly, because it will be underpowered.
Buddy-Matt@reddit
Not shorter, cheaper and shitter.
An extension cord will fail a PAT test if it can't support 13amp (source: this happened to my department years ago). I.e. it's a basic sagety requirement that an extension cord should support 13amp.
UniquePotato@reddit
Like all extensions leads, don’t leave part coiled up when being used.
Pedantichrist@reddit
You are golden. Crack on.
Forward-Swimmer-8451@reddit
Yeah chaining is grand . The problem with extension leads is fire from overheating so if you had 8 products like electric fires plugged in all linking to one house socket...
But one strimmer to one house socket is fine
the_Athereon@reddit
Basic math problem
If the 1st extension lead is rated for 13A, then whatever you plug in always had to add up to less than that.
Even if it's 20 items, so long as the total load is less than 13A you're safe.
the_uk_hotman@reddit
You can get a really long extension reel. Its not going to do anything if its just that and both extended fully and not over lapping. Just a trip plug between extensions if anything its for you and that extension as you can't assume that they are safe. Always turn power off before removing and plug
AffectionateJump7896@reddit
There are two separate issues here
With multiple "extensions" you can overload the plug that is at the 'root' of a a tree of extensions. This is solved by being sensible and not having 10 high power devices downstream of the first plug.
Extension leads have resistance. They are often quite poor quality and therefore high resistance - good enough quality for their length, but not excessively good. The problem is that chaining them together gives on extension of more than intended resistance, and a large voltage drop. You're losing voltage in the extension cords, so not enough voltage gets to the device. Realistically the worst thing that will happen is that the lawnmower will be a bit weak, or not work, due to the reduced voltage.
You should also ensure the extension cords, if they wind up, are fully unwound as that helps dissipate the heat produced by the resistive losses.
contemplating7@reddit
Looking at the comments already, the general gist is that it's fine to do. With multiple plugs and sockets outside, if you for some reason dragged it across and the joined part fell in a pond it would obviously cause an issue.
If you have some really old thin wired extension cable, I'd consider getting something newer and thicker. All my outdoor extension leads have a 3kw so I have an idea what to expect from them (fully unwound).
I have a 45m cable which I can plug in to the socket outside the kitchen is the only way to reach my car to vacuum it.
Previously, I had a 25m, then join others on but it because such a faff, I went for a cable that would be suitable for that one job.
An alternative:
Depending on the make of your strimmer, you might also be able to buy a longer strimmer cable which may plug straight in.
AmazingRedDog@reddit
It’s really not recommended given it’s a high power tool.
Much safer to make the one off purchase of a proper heavy duty extension cord with built-in RCD protector (it cuts the power if overheats or cable gets cut).
Make sure you fully extend (esp. if it’s a reel) before using.
LazyEmu5073@reddit
It's a strimmer, not a high powered tool at all. Probably about 500 watts.
OP, it's fine to daisy chain for a strimmer.
AmazingRedDog@reddit
Thanks for the downvotes😔
I’m not deleting my original advice trying to keep OP safe.
OP said in their post that it was a metal strimmer that needs a “heavy duty cable due to high power”. Metal strimmers (vs cheap ones) are in the 800-1000W range.
Running \~1000W continuously over 25–30m. That’s exactly when cable losses and heat start to matter
Incident-Putrid@reddit
Fully extend it though anyway. They get HOT. REALLY HOT 🔥
Altruistic_Cress_700@reddit
Definitely. Strimmer is a tool used continuously for many minutes
LilacScentedStoat@reddit
Fine as a one off , but I'd get a longer reel extension anyway to save the faffing about next time.
Or a battery strimmer.
Or put a little fence in and grow a little wild garden for the bugs in the bit you can't reach.
Snoo-84389@reddit
Daisy chaining a couple of extension leads together to temporarily run a single strimmer or lawn mower is absolutely fine (I've done it my self).
What is dangerous is permanently adding multiple other appliances onto each of the plugs available on each of those extensions blocks. That is what leads to overloading them!
Fanny_Flapps@reddit
The majority of "things you shouldn't do" regarding electricity is just a more politely worded "things absolute dipshits shouldn't do"
Yes it's fine
Riquende@reddit
There's also an element of "We told you not to in the instructions so we're legally covered if you did anyway in an unsafe manner and killed yourself" with some appliances.
Colleen987@reddit
It’s fine to daisy chain them, but also B&M have 25 metre spools for £15 a the minute
kipha01@reddit
Only if you're plugging in no more than the starting extension, even then you should consider draw, just because an extension lead has 6 sockets doesn't mean you can run everything plugged in at the same time.
wimpires@reddit
Trimmers only use like a few hundreds watts, won't be used continuously and will have nothing else plugged in.
Technically, no, you shouldn't.
But realistically it's fine.
twonaq@reddit
In this case it will be fine. What wouldn’t be fine is if you had one running to the washer and dryer then one off that going to the dishwasher then one off that going to the fridge.
Koda614@reddit
This is absolutely fine.
When people say extension leads, they usuall mean the power strips where you can turn one socket into many. Daisy chaining these is bad because it's easy to overload by plugging loads of things in which can melt the cable or even start a fire.
An actual extension cable, or even these power strips are absolutely fine to daisy chain a few together to get extra length as long as they aren't overloaded.
Vladamir_pootinn@reddit
Daisy chaining is never recommended but as long as you’re with the strimmer and you don’t overload the socket then you’re fine
Proof-Order2666@reddit
As long as that’s it nothing else then yes.
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