UK Mains Plug - Earth Pin on IEC lead Dangerous Fault - Page 1
Forum section: electronics / general

author: bookaboo
author_rank: Frequent Contributor
timestamp: November 27, 2014, 11:55:45 am
content: Has anyone ever seen an earth pin on a plug that looks like this:I don't know where it came from but this little lead has caused me a serious amount of trouble.I had it powering a Weller PU81 soldering iron (though it probably isn't the original lead) and have just found it to be the cause of the wildest of goose chases. I was working on a colpits oscillator circuit that developed a fault, found one of the two N=Channel mosfets faulty, replaced it to no effect. Traced the circuit up and down, removed the other N-Channel, found it faulty, replaced it to no effect.... rinse and repeat this cycle several times. At this point I'm sure its something in my circuit that's popping the mosfets.... so I build another... still popping mosfets.So I start to question my components, BS170 from Farnell, test OK on the Peak Atlas component tester, no problems.I suspect static, but Ive never had a problem with that, certainly not on this scale. The mosfets are popping on power up (or so it seems)In desperation I fit then remove one before it's even powered up and find it faulty, at this point I'm sure its static but decide to test another theory..... I touch a brand new one out of the pack with my Weller and its faulty!!I get out the gas Iron and fit two new mosfets, the circuit fires up instantly!I test the continuity from the iron tip to the earth plug pin, it's around 25r Im not sure if thats normal, I always assumed a direct short to earth. Then I plug in and test to an earth point.... open circuit. I presumed a faulty socket, replaced it to no avail then noticed the insulation on the earth pin here. When I use another IEC lead the iron is earthed correctly (well 25r anyway).I have never paid much attention to mains plugs but I dont recall seeing one with any insulation on, logic says it would be better without insulation surely. This fault was a massive hassle, but could have been much much worse.The other question is whether the socket is also partly to blame, maybe a case of two substandard parts coming together to cause the fault?I'm also wondering if there's a fault in the Weller as well, obviously it needs an earth for safety but in a non-fault condition shouldn't the tip just float? Note that the circuit I was working on was battery powered the entire time, totally isolated.Edit -I've done a little googling and it looks like this certainly is a fault.... probably a case of "sort by price" importing again.http://www.bs1363.org.uk/I don't recall specifically buying IEC leads, I have loads lying around from various equipment so unfortunately I can't identify the source. Another one to be aware of

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 27, 2014, 12:21:29 pm
content: Certainly shouldn't be insulation on the earth pin - actively dangerous

author: Monkeh
author_rank: Super Contributor
timestamp: November 27, 2014, 12:31:16 pm
content: That is very much a non-compliant plug. The earth pin should either be solid brass (usually nickel plated) or entirely plastic (for double-insulated devices only).These crop up all the time on cheap imported stuff. Twist all the pins off with a pair of pliers and dispose of it.

author: bookaboo
author_rank: Frequent Contributor
timestamp: November 27, 2014, 12:36:33 pm
content: Yeah thanks guys, I'm going to have a little therapy with this plug, a block hammer and a concrete floor.

author: Towger
author_rank: Super Contributor
timestamp: November 27, 2014, 01:16:18 pm
content: Quote from: bookaboo on November 27, 2014, 11:55:45 amThat's a Chinese BS1363 plug. I bet if you cut the wire open it just has few strands of copper plated steel wire rather than the .75mm (or what ever is) stamped on the cable side. Send it to the bin...

author: bookaboo
author_rank: Frequent Contributor
timestamp: November 27, 2014, 01:25:05 pm
content: Indeed "0.75mm"

author: Towger
author_rank: Super Contributor
timestamp: November 27, 2014, 01:31:06 pm
content: Think of the fun you could have by plugging it into a 3kw electric kettle, no need for Photonicinduction's 'Big Boy' power supply.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: November 27, 2014, 01:46:37 pm
content: Quote from: mikeselectricstuff on November 27, 2014, 12:21:29 pmIt's not by code, but how is it actively dangerous? I would presume that it is sufficient that the earth pin makes first/breaks last and keeps contact when plugged in. (Ignoring the rest of the poor construction of this plug and cable.) Or does the socket only mate with the earth pin near the socket?

author: wraper
author_rank: Unknown
timestamp: November 27, 2014, 02:14:28 pm
content: Quote from: nitro2k01 on November 27, 2014, 01:46:37 pmYes it does.

author: bookaboo
author_rank: Frequent Contributor
timestamp: November 27, 2014, 02:49:23 pm
content: http://www.bs1363.org.uk/assets/images/Sleeve_detail.jpgNot the clearest of images but you can see here what would of been happening.

author: SeanB
author_rank: Super Contributor
timestamp: November 27, 2014, 04:06:27 pm
content: Typically the plane of contact for all 3 pins would be similar, the earth pin only being longer so as to actuate the socket shutter and guide the other pins during insertion, as well making contact first and breaking last during insertion and removal. This last will mean that the contact has to be right behind the shutter, and with the insulated plug this places it in the region were the plastic sleeve is, so it effectively floats.As well with the shoddy casting ( you can see the porosity in the brass bar used as surface cracks, probably it was the cheapest most impure recycled dross they could get that had some copper in it, and probably lead, tin and all other contaminants as well to boot) and poor machining and workmanship it probably also had intermittent contact to the earth lead as well.

author: Zero999
author_rank: Super Contributor
timestamp: November 27, 2014, 04:21:52 pm
content: Quote from: nitro2k01 on November 27, 2014, 01:46:37 pmIt's dangerous because the connector always makes contact with the part of the pin nearest the plug, so if there's an insulated sleeve at the top of the plug it won't make contact with the socked when it's fully inserted and therefore won't be earthed.

author: electr_peter
author_rank: Unknown
timestamp: November 27, 2014, 07:45:24 pm
content: Plug in the picture is clearly fake and illegal due to plastic shroud on ground pin. I have recently seen several items on ads showing very similar UK style plug - I would look very carefully at those item in terms of safety/quality.UK has a strict (and very visual) standard for plugs - one look at picture and it is clear that something is not right.

author: Dave Turner
author_rank: Frequent Contributor
timestamp: November 27, 2014, 07:58:08 pm
content: To complete the picture a for fully compliant plug AND socket the shrouds on the live and neutral pins are designed such that connection to the supply is only achieved after the shrouds are within the faceplate of the socket.

author: amyk
author_rank: Super Contributor
timestamp: November 27, 2014, 09:52:39 pm
content: Does it cost all that much more tonothave the plastic around the earth pin? It doesn't seem so difficult to copy that aspect of the design, especially when it's standardised and you can find copies of the standards on Chinese sites...

author: SeanB
author_rank: Super Contributor
timestamp: November 28, 2014, 05:19:26 pm
content: The extra brass costs 5c, and the plastic is 1c, so guess which one wins.