Loosely Comnnected

This is quite a wierd one: some time ago at a company I work for sometimes, a colleague tried to replace some old 15″ LCD monitors with shiny new 19″ ones, to be confronted by extereme flickering. I had a look, tried the monitors with my laptop, and got a flicker-free picture. I made sure the leads weren’t too close to mains cable, but no change.

We assumed some incompatibility with the (elderly) PCs, and another colleague changed the PCs recently. In the course of doing so, he discovered the real cause. A power lead- just a normal BS1363IEC C13 (colloquially known as a kettle lead), but, tellingly, with a rewireable BS1363 plug, not a moulded one. Remove the lead, problem stops. This lead was connecting one of the PCs that was working perfectly well, and flicker-free with the 15″ monitor.

I looked at the lead the next day:

The culprit: a badly fitted plug.

The culprit: a badly fitted plug.

and it seemed kind of OK at a glance, though that neutral lead should have been cut shorter.

What did turn out to be wrong was every terminal was loose: loose enough to turn by hand, so I presume that the intermittent connection caused enough noise to upset the new monitor, but not the old one. Disturbingly, this lead had passed a current PAT test, when potentially it’s a fire hazard: loose connections can overheat.

I don’t know if the connections had worked loose (which is one reason why connections in screw terminals should not be tinned with solder) or just sloppily fitted in the first case. The plug did rattle when shaken, but it would do that even with tight terminals, as the pins have a bit of play in the housing. Full marks to my colleague for spotting an obscure fault.

2 Responses to “Loosely Comnnected”

  1. Species5618 Says:

    being on a computer did it get a proper PAT test, or a visual inspection.
    in a visual inspection case, I rushed tester may have not look properly and assumed it was a moulded plug…

    PAT testing is a great idea, but like many other things we have to do these days falls into my “you can legislate against stupidity” box

    I recently has a similar surprise. my air bed pump, fitted with a non moulded plug from new, pulled the brass insert from the lid, leaving an exposed and potentially shocking set of wires

    and one of my sewing machines, (yes I have more then one), is an old 70 machine and still HAD a plug with non insulated L & N pins on it !

  2. stymaster Says:

    I think this just got a visual. You have to remember too that PAT testing is boring as fuck. so the tester gets bored.

    I think I can beat your sewing machine: the one slide projector had an unsleeved plug, and the easily-removeable cover over the lamp exposed a frightening array of hefty HV components.