Belter from HT

An occupational hazard, isn't it?

Yes, but with proper care it can, and should, be avoided. Lamp posts are a hazard but I don't go merrily riding into them.

[Sideband]

Really curious to see what the induced voltage actually was!

Pretty high...especially when I broke down one evening (the car that is...not me) on the way home and in semi-darkness was trying to find where my sparks had gone.....! It was 1979, a Wolsely 1800 automatic, only a basic tool kit and an uninsulated screwdriver. Poking about around the points, one hand on the front grille and the other holding the uninsulated screwdriver while opening the points......It's amazing how far one can throw a scewdriver under those conditions!

[HamishBoxer]

And words that would get us all banned from the forum!

[KeithsTV]

Back in the late 60s I'd been given the chassis of a Bush radio gram. This had a single pole switch and a non isolated chassis so could be wired such that the chassis was either live when the set was on or when it was off. The screw for one of the knobs had been lost so I'd fitted a 4BA screw and the knob was fitted to the control with the on/off switch. I was experimenting with a simple circuit that lit a bulb when it detected RF using the LO from the Bush set as my RF source. I then discovered that this circuit worked much better when earthed. So there was I with the probe in one hand poking it into the LO and watching the lamp light. With my other hand I turned the set off touching the exposed screw which sent the full 240V through me to ground as the set switched off. On hearing the yell my mother came rushing up the stairs to see what had happened. Fortunately the shock must have caused me to drop the earthed RF probe and pull away from the chassis.

Several years later I was building a mains power supply for my transistor radio and had it all running quite nicely so decided to put it in its box. Using my un-insulated metal BIB wire cutters I cut through the neutral wire, fortunately leaving a single strand of copper uncut, then proceeded to cut through the live wire. Again fortune was on my side as the wire cutters were touching the single strand of the neutral wire. The resulting bang as the cutters touched the live wire blew not only the fuse but took a chunk out of the cutters and the radio went off. I should have realised that as the radio was being powered by the PSU the mains cable was live. I always check the mains is off and disconnected now!

Keith

[ionburn]

Most (amusing as it turned out) shock I have had was an RF burn from the top cap of PL504 in BRC 1500. I was working on the set and felt an itch in my nuckle. When I looked I noticed the familiar blue arc from the top cap to nuckle. As it was RF I didn't feel a shock as such but on retrieving my hand I noticed a white spot like soldering iron burn.

It did heal like any soldering iron burn with no after effects.

Shocks were not uncommon in those days but I realised at an early stage that more injuries were obtained from gashed hands when recoiling from a shock than the shock itself so (although many do not believe it) I trained myself to stop the instant I moved to avoid that likelihood.

[Peter.N.]

The shocks you got from the old deep cabinet TVs were not so much carelessness as awkwardness, you had to get practically your whole arm in the cabinet to reach anything at the front so there were many things that you could and often did come in contact with, the pain came not so much from the shock as the hasty withdrawal of your arm, the backs were often secured with screws that went into right angled brackets that nearly always had sharp corners... I will leave the rest to your imagination.

Peter

[Phil G4SPZ]

As a boy, my skin was sensitive enough to feel a tingle when I put my hand across the rails of my Tri-ang train set. Yes, just half-wave rectified DC at 12 volts. I've been pretty careful and (mostly) shock free since, but the most painful shock I remember vividly was from the spark plug of a motor mower. Crikey, that hurt.

[Hartley118]

Originally Posted by Phil G4SPZ

As a boy, my skin was sensitive enough to feel a tingle when I put my hand across the rails of my Tri-ang train set. Yes, just half-wave rectified DC at 12 volts. I've been pretty careful and (mostly) shock free since, but the most painful shock I remember vividly was from the spark plug of a motor mower. Crikey, that hurt.

How nostalgic I remember those model train shocks. In my case, it was another example of inductive surges. I had (and still have somewhere in the loft!) a Trix Twin railway which runs on 20V AC using series wound motors.

In order to select reverse, the engines incorporate a substantial stepping relay to reverse the field winding, the relay coil being operated by interrupting the 20V supply. This sequences through forward-stop-reverse-stop-forward.

The back EMF from the relay coil inductance certainly delivered a fair old belt if your hand happened to be on the track at the time of operation! The major design snag is that the relay also operates if there's any loss of contact due to dirty track etc, so best to keep the hand clear of the track anyway because you never knew when the back EMF might happen.

Martin

[wireless_john]

OK, here's my first serious belt. It was in 1973, I was on HMS Eskimo and I managed to touch 7kV on a JDA radar display. Working on it in the dim light of the ops room. My arm hurt for ages after that but it was a lesson I never forgot!

[Biggles]

Brings back a few memories, scratching around in darkened control rooms, by the light of a pencil torch held in your mouth (nobody seemed to have heard of head torches then), keeping quiet as a mouse, and trying to read the cable harness number which was always at the back of the cabinet with the label half way through a hole in the metalwork. On the subject of drawing arcs, the most spectacular one I remember was while working with a colleague on a 300 Watt AM Pye transmitter, sometime in the Eighties. You had to balance "the flags" which really meant adjusting two pieces of metal (capacitors) with a long screwdriver to balance the two 4CX250B output bottles. You had to be careful the adjustments didn't get out of sync with you keying the transmitter, otherwise as my mate found out you draw an RF arc out of the PA compartment which in his case extended to about a foot as he recoiled from the beast at a good rate of knots. Another time while working on the same type of equipment at a main site a colleague of mine managed to trip the ELCB by getting himself across some live equipment. That's why we always used to leave the door open to the hut so if the power tripped you could still have some light to find your way out.
Alan.

[Oldcodger]

Originally Posted by ionburn

Most (amusing as it turned out) shock I have had was an RF burn from the top cap of PL504 in BRC 1500. I was working on the set and felt an itch in my nuckle. When I looked I noticed the familiar blue arc from the top cap to nuckle. As it was RF I didn't feel a shock as such but on retrieving my hand I noticed a white spot like soldering iron burn.

RF burns- I don't know if there's any others posting that worked on the Clansman 353 on the bench, but I don't know anyone who hasn't had a 50w VHF burn whilst tuning a transmitter. The smell hits first, and then you realise that the point of you finger has burnt.
But ,how many of us are ex GPO/PO(T), who remember jumping on a UAX MDF, without some protection on the back of a hand. 50 V might not seem much, till you hand slips and it's sweaty and the 50v or ringer burns.

[Biggles]

Yes, getting bitten from telephone lines is a bit of an accepted thing. In my present job I work on telephone equipment a lot and most of this is outside. Kneeling on damp grass in front of a cabinet or post joint (when the old landrover seat cushion "insulated kneeler" is out of reach in the back of the vehicle) it's surprising how nasty a 50 volt shock can be. It definitely makes you recoil and as said before it's worse if the line is ringing at the time. There is even more of a risk of a tingle while fumbling with jelly crimps on U/G joints on a soaking wet day while halfway down a hole.
Alan.

[Oldcodger]

Biggles- now think back a lot of years, to days when we climbed poles with a few layers of wires. Run the dropwire to the house and fix it on pole.To connect to DP, and then your ears contacted with an open copper wire. I've done both -up the pole and down the hole.

[julie_m]

I supplemented my university grant by repairing appliances, though I refused to touch televisions -- I was afraid of live chassis and EHT, and I'd heard horror stories from my Dad and Grandad (but see later).

Then I got a "proper" job in electronics, as a technician in a development lab -- and ended up working with gas ignition controllers.

Don't try this yourself, but when you get 25 kV up your arm, you know about it, for the rest of the day. I've also had a few doses of mains.

And now I'm working with computers, and TVs don't have such nasty voltages inside them anymore; just proprietary parts that are too expensive, if obtainable at all, for it to be worth repairing a set as opposed to just buying a new one.

And I still cry when I think of the potential money I turned down out of such a stupid fear ..... After all, most people don't die. And the poor unfortunate victims in the horror stories that shaped my opinion, who were killed or maimed while experimenting with old TV sets, probably were working with really old sets with mains-derived, essentially non-energy-limited EHT as opposed to intrinsically energy-limited flyback EHT.

[beery]

I had a really nasty shock when I was a technician in the education sector.
I was trying to diagnose a fault on a Hameg scope (it turned out to be a dead CRT).
Knowing the danger of poking around the CRT with a meter, I had plugged it into our portable isolation transformer (this was used specifically for these kind of repairs) which had been put together in house. I also had one arm in my pocket.
Anyway, somehow I managed to slip with the meter probe and received about 2KV which through me off my stool and made me feel exhausted for the rest of the day.

I was left wondering how I got a shock with one arm. I went back and checked the isolation transformer and found that it had a direct connection to earth on the earth pin of the socket. I checked with the senior technician in the department who said he had added the earth connection to enable the transformer to pass the PAT test!
I never used that isolation transformer again...

I myself am much, much more careful around EHT. I think I was very lucky.


Cheers
Andy

[MotorBikeLes]

Like most, I have had my share of big shocks. My most stupid one (discounting the big one off the back of a Wylex cooker plug aged about 12) was while I did a spell testing colour tubes. I had modified a series of chassis, where I hung the CRT on hooks thro top mounting holes. I had a sprung length of "dag wire" to ensure dag contact, and a pointed probe to discharge the cavity after testing.
But of course one day I left the set switched on, and just pulled off the EHT connector. Not sure why I did not switch on, or poke the probe under the cap first as usual, but it was a belter.
However, regarding FATAL shocks, there was a technician around that time who was repairing a microwave. His shock was fatal. I did not know the guy, but the other engineer I worked with did, and he said he was good at his job, until that day.
Les.
Les.

[Peter.N.]

A microwave supply is on a par with the mains EHT on early TV's, I really was wary of that, flyback EHT just bites.

Peter

[hannahs radios]

One thing I'm guessing that the new generation of phone engineers won't have the shock risk for many more years the only place where there's a y voltage is in the new little green cabinets that are everywhere the rest is all fibre

[Lloyd 1985]

Forgot to mention my other 'stupid boy' moment, trying to draw a spark from the anode of an EHT rectifier in 9" 405 line telly, with what looked like a well insulated pair of pliers, I thought 'they'll do the job' as they had nice thick rubber handles, well, they certainly drew a spark!! And I felt it! turned out the nice thick rubber handles are 'anti-static', or static safe, whichever you prefer... Not insulated at all!

[Oldcodger]

Originally Posted by hannahs radios

One thing I'm guessing that the new generation of phone engineers won't have the shock risk for many more years the only place where there's a y voltage is in the new little green cabinets that are everywhere the rest is all fibre

From what i've seen in cabinets, connections are IDC on what is commonly called KRONE strips, and I'd imagine that MDFs are now likewise, so they will never know the joy of jumpering on an MDF, with sweaty hands meeting only 50v ( occasionally ringing voltage about 90 on adjacent circuits), and getting a belt. Hand jumped off tag for back of hand to get stabbed by tags on next block and back to live tags.
Not to mention the joy of working on an open wire DP in damp weather. 90V ringing is not high, till your ear contacts it