A Blog About Those Pesky Plugs, Flexes, and Extension leads
By simon Gallaway, Feb 2025
This is a blog for trades people and householders about the ins and outs of portable electrical appliance plug and flex safety.
‘Plugs and flexes? But they’re the boring bits’, some might say.
Well ok, they’re not as exciting or as complex as the business end of a money-spinning £6000 floor sander. but their condition can cause that £6000 machine to end up toasted, and worse, the cause of fire, property damage, a damaging insurance claim or worse still – a dishonoured insurance claim, possibly even death, and a case of manslaughter. You don’t want to risk that for the sake of knowing what tell-tale signs to look out for do we?
Plugs and flexes are in many ways far more vulnerable to abuse and damage than the machine itself. I mean, how easy is it to ‘accidentally’ run over the flex with a 36 grit pad and expose the live conductor in about a second? You couldn’t accidentally run over a belt sander with another sander.
This is worth a thought. How happy are your staff members? Odd question isn’t it?
Well it’s a well-known fact that bored or frustrated staff tend to put machines in a dangerous condition by breaking them ‘accidentally on purpose’ so they don’t have to use them. But if they like the job and take pride in what they get paid to do, they will try to preserve the equipment instead of breaking it, won’t they?
Plugs and flexes are also vulnerable to bad practises, being badly repaired by people who don’t know any better, or not very practised, or impetuous to ‘get it working’ without wasting any production time. Plugs and flexes are simple enough to make many believe they can delve in, while they wouldn’t dare go inside a complex £6000 sander.
So, let’s make a start and look at some of the tell-tale signs and horrors that pass my way on the Generation Game conveyor belt that is my job machine repair schedule. (Nice to see you, to see you, nice!!!) for those ancient enough to remember Bruce Forsyth, like me.
For clarity, throughout, we refer to electrical load both in terms of current flow in Amps, and power consumption in Watts, or more conveniently in kilowatts, kW, when we’re talking about thousands of Watts. K, or kilo, just means times a thousand (but not for killer whales).
For our purposes they are interchangeable. The most you should try taking out of a 13A socket is, well, 13 Amps, or 3kW. Watts is Amps times Volts, and as household mains Volts is always 230(ish), 1Amp times 230Volts is 230Watts, so 4Amps is roughly 1000 Watts, and that’s when we start calling it 1kW and so on.
Different appliance classes and their plugs
You are likely to meet two types of appliance; Class 1 and Class 2.
Class 1 appliances must have an earth wire going from the plug into the flex, and out of the flex at the other end and onto some metallic part inside the machine.
Class 2 appliances have sufficient electrical safety features that they don’t need an earth wire, and this is indicated on the machine’s rating plate, as a ‘square inside another square’. See photos
Sometimes this sign will simply be moulded into the plastic body.
The simple rule is; if it doesn’t have this sign – it MUST have an earth wire.
Below are what good class1 and class 2 plugs should look like.
Tip 1. Make sure the earth terminal screw on a class 2 plug is tight; it might not have a wire to tighten onto, but what happens when a loose screw comes out and starts rolling around inside a live wire area? It can touch things it didn’t ought to and cause problems, can’t it!
While we’re looking inside plugs, I’ll show you some horrors that can compromise their safety and explain what’s wrong.
Tip 2 The strain relief clamp (that bit of white plastic with two screws restraining the flex) should ALWAYS clamp across the outer sheath of the flex, NEVER just across the individual wires, so that any incidental tension is taken up by the tough outer sheath and not tending to pull the wires out of their terminal posts. I see this a lot and it’s baaaad!
Tip 3 When wiring a plug, aim to make the live brown wire as short as possible, the blue wire no longer than necessary, and the earth wire plenty long.
Why? Because if the strain relief fails, the resulting tension from being pulled will tend to make the brown live wire pull out first. The brown wire gets its live voltage from the terminal post, so if they part company, the brown wire goes dead, and safe, while the green/yellow earth wire is still connected and doing its job of safety protection.
That’s why the terminal posts are arranged the way they are.
Plug and flex assembly faults
A little too much exposed live wire conductor. The insulation should ideally go right up to the terminal post.
The fuse is so far displaced in its clips that it might even start making and breaking contact, which would cause sparks, heat, and eventually meltdown
Missing terminal post screw(s). As in the last photo, if the wires aren’t solidly connected to their posts, they can arc and spark, build up heat and melt.
Tell-tale sign of this would be intermittent machine faltering, which could damage the machine as well.
The flex shows signs of being bent acutely at the point where it goes into the plug This is the early stages of a flex breakage. Why does it happen here more than anywhere else?
If you bend a piece of flex somewhere in the middle of its length, every point bends gradually to the same degree along the length over which it’s bent. But plugs don’t bend, so at that point, the flex has to accommodate all of the bend at one very concentrated point and it becomes an aggressively focussed kink. It’s enough to break it!
Melting point
Tip 4 A developing electrical fault in a plug will often make it get hot. Without so much as reaching for a screwdriver, you can run your hand across a plug while in use, to see how it feels.
If it feels warmer than the room temperature, have the cover off and check it for faults and signs of getting hot. The photos that follow, all have common signs to look out for.
Can you see the brown stain round the fuse, the melted plastic of the plug in the background, and the melted tip of the orange outer sheath?
Why did this happen? Yer, the live wire terminal lost its screw because it wasn’t fitted by a competent person, the wire kept sparking on the post, and sparking makes things hot enough to melt.
This is what happens if that ‘incompetent’ person’s work wasn’t checked. You know what the next stage is? Possibly fire.
Melting round the base of the live pin is a very common sign to look for, and this will remain even when the appliance is not in use, which means it doesn’t need to be in use for you to notice that there’s a problem inside it.
Tip 5 train your eye to look at plugs and pins whenever you see them. Training your sight, smell, and touch are the tools in your armoury for catching electrical disasters brewing. Let your senses interrupt what you’re doing when they need to warn you.
You wouldn’t believe it, but all extension reels have two rated load limits; one with it unwound, usually 3kW (or 13 Amps) and one with it wound up, 1kW (or 4 Amps). Add up the rated current (from the rating plate/label on the machines) of the things you’ve got plugged into it and don’t exceed the limit. These do melt and they can catch fire if left long enough unattended. I have seen it happen.
No extension reels were abused in the making of this blog.
(The machines plugged in were for demonstration purposes and none were switched on)
Abuse
Sometimes we abuse things without meaning to. Do you remember the point about kinking flexes where they go into a plug? The same is much more common at the other end where the machine is. When you’ve finished using it, the conscientious intention is to tie up the flex for transport, or so that it’s no longer a trip hazard, so we wind it tight around the machine so it doesn’t unravel. Good, yes? No!
Many flexes are fitted with a long rubbery strain relief gland where it goes into the machine, to prevent it from bending round a radius tight enough to damage it. Well these only work to a minor degree, and it’s still very easy to break the conductors inside before the outer sheath looks visibly damaged. Look at the flex on this Sebo vacuum cleaner.
I’ve had to repair many of these, but they are easy because the flex is connected to a common ‘chocolate block’ connector on the inside. You can make a whole new flex if needed. But still, how’s it gonna look if you rock up to a high profile client and your first machine falters and you don’t know why?
Many up-market appliances are now made with separate plug-in flexes, like these Festool ‘Plug-It’ leads. They have factory moulded plugs at both ends. There used to be a re-wireable repair plug that you could buy when the wires break because the flex has been wound too tightly, but Festool got wise to that one and stopped selling them.
Now I believe your only option is to buy a new Plug-It lead for £30 (in 2024). Best thing to do is unplug it and coil it separately like this one.
999 times out of 1000, if you see electrical tape round a flex it means someone’s damaged the flex, possibly exposing a live wire with 240 Volts on it, and taped it up either to get through the job of the day, or trusting this is to be a good enough repair anyway.
It isn’t! And 999 might be the next phone number dialled. Hideous, isn’t it? And HSE could even discredit your defence if there were a death and they found this in your equipment, even if it wasn’t actually the cause
Overloading
A plug and socket will burn out if overloaded. Like this socket that was used for the ‘granny’ charger on a small electric car, even though the charger was rated at no more than the 13A limit.
This wall socket and multiway extension that were used for two 2kW fan heaters and various computer equipment definitely was overloaded.
It doesn’t always just have to be too many ‘current-thirsty’ appliances plugged into one socket, if the plug pins or the contacts in the socket are tarnished just enough to create a poor electrical contact between the two, the problems of substantial but not excessive current and poor contact multiply each other to cause this burn-out result.
But, it’s not actually an excessive number of things plugged into one multiway socket that counts as overloading. Theoretically you could have 400 of these 5W USB adapters plugged into one multiway socket, and it still wouldn’t draw more than 8A, or 2kW through the wall socket.
You have to get into the habit of gauging the current draw of each appliance. Generally, digital appliances take very little, machines with motors take a range of currents according to the weight of the motor, and anything that heats is ravenous!
Leftovers
Finally, don’t get drawn into this juicy example.
If someone asks you for a file to file off the bobble on the yellow commando plug because “the manufacturers put it in the wrong place and it won’t fit the blue socket”, it’s coz it wasn’t meant to. (I really have been asked this)
Yellow is for 110 Volt tools, as indeed all site trades people will know without needing to read it here.
Blue, or blue and white, is for 230 Volt tools.
If someone got far enough to actually connect these two, the machine would likely race away at six times the speed it’s meant to, and burn out soon after that.