Bodges

[PsychMan]

Funny you mention Arcs, Craig.

My late father was an industrial electrician for many years, and regularly worked on high voltage infrastructure. He was a very sensible man, and always took H&S very seriously. He did have one mishap however, which was caused by a combo of incorrect information being provided by a colleague, and as he did in those days, working very long hours.

He went into a high voltage substation or switching room to investigate a fault at night, possibly a tap change problem, I cant recall the technical detail now.

It wasn't supposed to be live, but it was. The arc and flash that occurred before him was enough to cause severe pain in his eyes, and temporary sight problems. He was VERY lucky, but still ended up in hospital all night, and it took some time for his eyes to return to normal after that incident.

The funny part of this is when it happened, he immediately took off his hard hat and threw it down in anger. A colleague came in quickly after and said:

"Thank God! You're Alive!! I saw a huge flash, heard a big bang, and then I see your hard hat rolling out the door!"

[emeritus]

At Plessey's the labs had wall sockets for a 400Hz 120V 3 phase supply for powering avionics equipment. The supply was obtained from a motor-generator set in an outbuilding, and was only run up when needed, which was not very often at the time I was working there. On one occasion it seems that the circuit breaker kept tripping when the engineer attempted to start it. Rather than investigate the reason, he wired it closed, resulting in smoke issuing from behind the metal partion in the lab where the short circuit was located!

[Dave Moll]

Originally Posted by PsychMan

A colleague came in quickly after and said:

"Thank God! You're Alive!! I saw a huge flash, heard a big bang, and then I see your hard hat rolling out the door!"

No doubt, the colleague was mightily relieved that said hard hat didn't roll out with a head still inside it.

[Andy Doz]

Originally Posted by emeritus

At Plessey's the labs had wall sockets for a 400Hz 120V 3 phase supply for powering avionics equipment. The supply was obtained from a motor-generator set in an outbuilding, and was only run up when needed, which was not very often at the time I was working there. On one occasion it seems that the circuit breaker kept tripping when the engineer attempted to start it. Rather than investigate the reason, he wired it closed, resulting in smoke issuing from behind the metal partion in the lab where the short circuit was located!

This brought back some memories. I was an apprentice at Smiths Industries in the 80's. There was a 400Hz, 120V supply there, which, at our end of the factory was a damn sight more reliable than the 240V mains! ... You'd come in in the morning, and find the kettle connected to it... "No mains again!", and the kettle gently humming at 400Hz... took a while to boil though ...

[Hartley118]

Originally Posted by Craig Sawyers

.............
........at University I was building a pulsed carbon dioxide laser. ........

What an exciting University course!

Did the CO2 laser work?

Martin

[Maarten]

Originally Posted by PsychMan

The building company, in the end reluctantly replaced the failed devices, but no PAT testing was done.

I didn't work there for much longer, but I wonder how many devices would have failed the PAT tests when they eventually got round to them..

I don't think PAT testing would have revealed much. The allowed withstand voltage for insulation and Y capacitors is a few kV. Mostly tested during a number of seconds, but a few minutes at 400VAC would usually be okay. Maybe one or two RIFA's that were on their way out anyway.

Probably the best inspection on devices that haven't fully failed, is to look for bulged electrolytics. The primary electrolytics in switching power supplies, the secundary electrolytics in conventional supplies.

[HamishBoxer]

Too true Maarten,sometimes the eyes are the best test equipment.

[Beobloke]

It's taken me a while to find the picture but the talk further back in the thread about badly wired mains plugs reminded me of the best one I've found on something I bought.

And, yes, obviously the item in question should also have had a 3A fuse fitted!

[Refugee]

Bodgers normally fit 13 amp fuses in order to be sure of a good audio output when it goes bang.

[G6Tanuki]

Crossing-over blue-and-brown doesn't really matter that much to me in the case of 2-core flex, specially when the 'thing' at the other end probably has a polarity-agnostic figure-of-8 2-pin 'cassette-lead' input anyway.

I grew up dealing with loads of things like table-lamps that had 2-core single-insulated twisted-pair power leads and single-pole switches in the lamp-fitting. Most-of-the-world doesn't fret about reversibility/polarity of 2-core power-leads and they don't seem to be getting-electrocuted at a spectacular rate.

[Beobloke]

Originally Posted by G6Tanuki

Crossing-over blue-and-brown doesn't really matter that much to me in the case of 2-core flex, specially when the 'thing' at the other end probably has a polarity-agnostic figure-of-8 2-pin 'cassette-lead' input anyway.

It didn’t. It had a hardwired mains lead and only a single pole power switch on the Live conductor, so definitely a bad idea.

[SiriusHardware]

Originally Posted by Dave Moll

Surely, anyone working on power cables worth his/her salt would check that power were absent rather than simply relying on being told so.

I remember seeing a documentary about the small army of workers who worked in the tunnels of the London underground overnight. One of them had a wooden board with a whole row of light bulbs on it in batten holders, something like 11 or 12 of them. This was his device for checking whether the line was live or not.

He was asked why so many bulbs and his answer was because it was very unlikely that all of them would be blown at the same time. Pretty sensible, I thought.

[Craig Sawyers]

Originally Posted by Hartley118

What an exciting University course!

Did the CO2 laser work?

Martin

Ah - it was during my Phd work. I was doing four-wave nonlinear mixing in liquid oxygen. The two waves were at 10.6um from the CO2 laser and at 1.06um from a Nd:YAG laser. We had the YAG, but not a CO2, and couldn't afford a commercial one. So I designed and knocked one up from bits around the labs, and from the university workshop.

And yes it worked.

If you want a little light (!) bedtime reading https://eprints.soton.ac.uk/393635/1/82032212.pdf

I'd ditched the CO2 idea by that time though.

Craog

[Michael Maurice]

Originally Posted by SiriusHardware

I remember seeing a documentary about the small army of workers who worked in the tunnels of the London underground overnight. One of them had a wooden board with a whole row of light bulbs on it in batten holders, something like 11 or 12 of them. This was his device for checking whether the line was live or not.

He was asked why so many bulbs and his answer was because it was very unlikely that all of them would be blown at the same time. Pretty sensible, I thought.

They would have to be connected in series though, for those who don't know, London underground operate a four rail system. The outer one is 440V DC, the inner one (in the centre) is at -220V.

[Dave Moll]

Presumably, they would have been a combination of series and parallel.

If they used, say, six in parallel - in series with a second six - that would serve for the +440V to earth. The -220V could then be checked across one set by having a centre tap. The parallel subsets would still provide that protection against a failed bulb.

[Brigham]

There was an old adage concerning the wiring of 15-amp mains plugs, which broadly said that, as long as the green wire went to Earth, the red and black could go either way.
Every time I mention this today, I get howls of disbelief; yet it is exactly the principle of the much-vaunted Shuko plug!

[duncanlowe]

Originally Posted by Brigham

There was an old adage concerning the wiring of 15-amp mains plugs, which broadly said that, as long as the green wire went to Earth, the red and black could go either way.
Every time I mention this today, I get howls of disbelief; yet it is exactly the principle of the much-vaunted Shuko plug!

Yet the Shuko is designed for use where Neutral isn't tied to Earth as far as I understand (but quite prepared to be told otherwise as my real experience is in automotive).

[eddie_ce]

Yet the Shuko is designed for use where Neutral isn't tied to Earth as far as I understand (but quite prepared to be told otherwise as my real experience is in automotive).

Not quite sure what you mean by this. Here in Germany, in older installations (TN-C system) Schuko sockets were fed by two conductors, the earth contact being bridged to the neutral in each socket. Thankfully this is no longer permitted.

With the TN-C-S and TN-S systems in use nowadays, Schuko sockets are fed by three conductors, in a TN-C-S sytem the earth (CPC) is often connected to the incoming neutral at the consumer unit, not necessarily at the DNO's service head as in the UK.

There is however no steadfast rule on the polarity of Schuko sockets.

[Refugee]

This old plug looks like it has been wired up by a vegetable.

[stacman]

Perhaps somebody read the instructions where it said, This appliance must be earthed.....