Wall plug a fire hazard

[Alex]

Quick story share. Just now I had a 3kW electric heater connected to a plug strip which is in turn connected to the wall socket.
The heater would cut out for no obvious reason and at random intervals.
Check the heater cabling, fine. Checked the plug stip cable, fine. The plug of the strip that connects to the wall was warm. Took that apart and to my surprise all 3 (!) screw terminals were loose. There was heat damage on the wiring. Fixed all that and it works fine now. This was a new strip I bought personally and the wall plug has only been connected once. I can only guess that the screws were never fixed properly at the factory and the issue manifested itself now that I used the high power heater. This is a plug with all the approvals...an excellent ignition source.

Stay safe.

[IanB]

Yikes! What bothers me is that plugs are often moulded on to the cable these days so you can't see inside them to inspect them even if you want to.

[G7PSK]

I have noticed plugs getting hot at nowhere near the rated 13 amps, always it has been on equipment which came with plugs fitted and the plugs made in China. I suspect that they do not conform to the standards that ore marked on them. I have a number of old MK plugs made in Britain that get recycled onto newer equipment when the old stuff goes, they never warm even with an overload.

[PStevenson]

I did a video for exactly the same reason (and to promote a cover of umbrella I did) but if you watch the first few seconds of the video I took a picture of a plug on something I was fixing for someone, if you think loose screws are bad you haven't seen anything yet! http://youtu.be/2-HX92KcFX0

[IanB]

I'm not so sure about tinning wires that go into screw terminals. I think the screw really needs to compress the copper strands into a tight bond. If you tin the wire the solder may slowly yield under the screw and give way over time leading to a loose connection, making the fire hazard you were trying to avoid.

[PStevenson]

I'm not so sure about tinning wires that go into screw terminals. I think the screw really needs to compress the copper strands into a tight bond. If you tin the wire the solder may slowly yield under the screw and give way over time leading to a loose connection, making the fire hazard you were trying to avoid.

the screws in UK plugs are pointed so you don't get a good enough bond unless you tin them, new appliances now come with little brass thingies over the ends of the wire.
the plug in that video was pure shit, usually there is a band over the input hole that stops the wire being pulled loose - sorry for my lack of proper words, my head is buggered from lack of sleep and I just cannot think of the right words for anything at all

[alm]

I agree with IanB, I wouldn't solder wires involved in mechanical collections (screw or crimp) or wires that have to flex (which is why soldering connectors is usually a bad idea). Solder removes the elasticity of the wires and is deformed plastically by the pressure, resulting in loose wires and fire hazards. Using a ferrule can be a good idea for stranded wire, although terminals in plugs should be designed to accept bare stranded wire. Who wires removable plugs with solid wire?

[Bored@Work]

Here local regulations prohibit tinning wires that go into screw terminals. Previously it was allowed to just screw in the bare stranded wire. These days, however, they must have ferrules.

[PStevenson]

well as I said, the screws are pointed and what happens is that when you screw them in, the strands just snap off. I do agree that tinning reduces elasticity but in this case it's the best of a bad situation.

and yes, "ferrules" thankyou, now I can buy some haha

[IanB]

Maybe the pointed screws are designed for use with ferrules? I don't remember pointed screws being that much of a problem in the past. I have the odd new and old plug at home, I'll have to take a look when I get home from work.

[pikuorguk]

My girlfriend has an electric bike, you'd love the charger that comes with it, it's finest quality Chinese with fake 'CE' sticker on it. The wires in the plug worked themselves loose so I took the plug apart to screw them back in. Someone in the factory had got the live/neutral swapped and had a nice chunky 13A fuse in there too.

The best bit though is the battery (24VDC) connects to the bike through a standard IEC C13/C14 PC-style lead. There's the same connector on the DC end of the battery charger too.

So yes, if you were stupid you could try to run your PC off the charger... or you could hook the battery directly up to the mains.

[Bored@Work]

Tinning is actually considered the worst thing to do.

First there is the process of cold flow. The tin becoming soft under pressure over time and the connection therefore becoming lose. IF you have pointy screws than it is easy to imagine that you have a rather high pressure on the tin, which should facilitate cold flow.

Then there is the issue of the tin having a much lower melting point then copper. When a connection is a little bit lose and some sparks happen the sparks do melt small points of the tin away easily and the connection becomes even more lose.

[Kibi]

I've been assigned to do some PAT testing now because the normal PAT testing guy is useless.
The PC power cords are rated at 6A (0.75mm2 cable), however, the moulded plugs are fitted with 10A fuses. This would probably never be a problem, but I still have to replace the fuses with 3A or 5A ones.
The PC's are a reputable brand, supplied by a reputable supplier.

[vk6zgo]

I would not advise using a 3kW heater via a plug strip in any case,as the current is getting a bit high (12.5 A).
I wouldn't be allowed to do so in Australia in any case,as our normal GPOs are rated at 10A max,so we would have to have a 15A outlet fitted.
Heaters with that sort of rating would probably be hardwired.
You are not supposed to use solder in Oz,either,but a sneaky trick I have seen,is to solder just the tip of the wires to help prevent unravelling.

[IanB]

Standard household outlets in the UK are rated at 13 A and many devices (electric kettles, room heaters) are designed at 3 kW to take advantage of that. I get very bored with the wimpy slow 1.5 kW electric kettles here in the US that are at the limit of what the 120 V outlets can supply. I would import a 240 V 3 kW kettle from the UK if there was some convenient way of getting a 240 V outlet in my kitchen. Unfortunately I'd have to rip the walls apart to run a new circuit and I don't fancy doing that.

You probably shouldn't run a 3 kW load on a plug strip in an ideal world, but most of them are also rated at 13 A and should be able to take it.

[westfw]

I think a lot of high-amperage appliances in the US come with warnings NOT to use any sort of extension cord.
(and 3kW@220V is the same as 1500W@110V, amps-wise.  And it's the I^2R heating in the wiring/connectors that causes problems.)

[Rerouter]

our gpo's are rated for 10A, but any good sparky would run wire rated to 13A, then again, they are hard to find today, heck its hard to even find ones with a valid or non expired one these days,

I have seen some of the dodgier ones running 7.5A rated for GPO's, so yeah, if you need 3KW, use a 15A gpo, worst case they run 13A rated wire, and that still covers 3KW

[slateraptor]

Just now I had a 3kW electric heater connected to a plug strip which is in turn connected to the wall socket.

That's a pretty good way to start an electrical fire. Was there not a clearly visible sticker on the power cord explicitly warning against the use of extensions and multi-plugs?

[Alex]

Just now I had a 3kW electric heater connected to a plug strip which is in turn connected to the wall socket.

That's a pretty good way to start an electrical fire. Was there not a clearly visible sticker on the power cord explicitly warning against the use of extensions and multi-plugs?

Is it? A plug rated at 13A should be able to take 13A at 100% duty cycle. Nothing to add to that. The strip also had a small linear psu for a cordless phone. The total current is below 13A. Yes, I will have losses with any extra extension lead, but I should not have fire hazard issues no matter how many strips I decide to connect in series, provided of course that the rating of one at the start does not exceed 13A (and even if it does, I should still not have a fire hazard because of the fuse).

This was a quality control failure at the plant which caused problems when the plug was pushed close to, but below its rated current.

[slateraptor]

Is it? A plug rated at 13A should be able to take 13A at 100% duty cycle. Nothing to add to that. The strip also had a small linear psu for a cordless phone. The total current is below 13A. Yes, I will have losses with any extra extension lead, but I should not have fire hazard issues no matter how many strips I decide to connect in series, provided of course that the rating of one at the start does not exceed 13A (and even if it does, I should still not have a fire hazard because of the fuse).

This was a quality control failure at the plant which caused problems when the plug was pushed close to, but below its rated current.

Didn't realize you're from the UK.

It's not uncommon to find plug strips without any overload protection mechanism in the US, although typical outlets are tied to 15A circuit breakers; I don't know how UK goes about their business. I've also personally seen a small electrical fire started when a friend decided to de-ice the front end of his Jeep with a 1.5kW space heater and 50-ft 13A-rated outdoor extension cord. About half of the cord was coiled in a bucket where the fire started so it was easy enough to contain, but that technically shouldn't have happened in the first place.

[amyk]

I've also personally seen a small electrical fire started when a friend decided to de-ice the front end of his Jeep with a 1.5kW space heater and 50-ft 13A-rated outdoor extension cord. About half of the cord was coiled in a bucket where the fire started so it was easy enough to contain, but that technically shouldn't have happened in the first place.

Extension cords are rated for operation in open air, not coiled up in a bucket. That decreases cooling enough to be dangerous.

[slateraptor]

Extension cords are rated for operation in open air, not coiled up in a bucket. That decreases cooling enough to be dangerous.

That's pure assumption; you'd be hard pressed to find any sort of derating specification on any commercially available extension based on physical orientation. Suppose I decided to use an outdoor extension cord fully stretched out on 125F pavement, let alone the sub-freezing ambient temperature when the electrical fire occurred.

[JuKu]

Really, don't tin wires. There is a very good reason why the practice is illegal in EU.

[grumpydoc]

That's pure assumption; you'd be hard pressed to find any sort of derating specification on any commercially available extension based on physical orientation

I don't know about the US but in the UK I would normally expect to see extension cable reels to be explicit that their rating is unwound from the reel.

Sometimes the lower rating when wound on the reel will also be specified - e.g
http://www.screwfix.com/p/masterplug-switched-4-socket-cable-reel-work-power-30m-13a/67915
Note the rating is given as "Unwound: 3120W, 13A, 240V. Wound: 720W, 3A, 240V", and there is a substantial difference (13A vs 3A).

The example where a cable overheated and caught fire mentioned that it was "wound in a bucket" - it should have been de-rated because of this, sounds like the user didn't realise.

[IanB]

Extension cords in the US come with a big warning on the packaging not to use them coiled up. Of course nobody tends to read the packaging, but they should.