On 18 Apr 2023 at 20:21:42 BST, "Stephen Packer" <stephen.packer@gmail.com>
wrote:

> On Tuesday, 18 April 2023 at 19:48:11 UTC+1, GeoffC wrote:
>
>> Maybe worth bearing in mind that it is usually a nice thick cable
>> connected more or less directly to the +ve battery terminal. If it's an
>> isolated terminal block OK but a bare terminal will, if it touches
>> anything metal, light up like an electric fire element for a few
>> seconds before it melts completely. Likewise, rings, watches, bracelets
>> etc are a no no during this sort of experimentation.
>> I once knew a mechanic with 9 fingers after an engine
>> block/spanner/ring/starter motor power terminal circuit completion
>> incident.
>
> Years ago I had to install a two way radio into a fuck-off big 'loader'
> in a quarry. It would just about fill a lorry with a couple of bucket's full.
>
> I'd just started working for the company and it was a difficult installation
> (the whole quarry was moving from FM to AM so all the radios needed to
> be replaced in a short period of time); I was working over the weekend to
> achieve this.
>
> The loader was the last vehicle to be done on a Sunday afternoon. I
> started working on it and... it was 48v electrics (which I hadn't seen
> before). The radio was 12v. I only had one 24v-12v 'voltage dropper'
> and I couldn't go without having a working radio in the loader so I
> wired it across the bottom battery (earth, +12v).
>
> The radio also had an antenna attached to the roof of the vehicle, which
> was grounded so the radio unit had two connections to earth (screen of
> coax, power supply earth).
>
> All well and good... except the vehicle was turned off by pulling an earth
> isolator.
>
> Now, I should have wired the earth of the radio to the output of the earth
> isolator, but I didn't. I wired it to the battery. Result was that the dash
> lights
> were lit.
>
> I spoke to the bloke who'd let me into the quarry explaining what I'd done
> and saying I'd be back on Monday to make a permanent fix and left a
> note in the cab: 'IGNORE THE DASH LIGHTS, MAKE SURE ISOLATOR IS
> CLOSED BEFORE STARTING'
>
> Of course, 5AM Monday morning, when the quarry started work, the
> shovel operator ignored the note, saw the lights on the dash were lit
> and turned the key to start... without closing the earth isolator.
>
> The coax running from the radio around the cab to the antenna apparently
> lit up 'like a christmas tree' shortly before turning to ash (as I assume did
> the
> power supply earth). Anyway it all evaporated leaving smoke in its place.
>
> I turned up with a suitable 48v 'dropper' at 8AM only to be confronted by a
> furious
> quarry manager (pre mobile phones so turned up 'blind') who accused me of
> sabotaging his quarry and stopping operations for three hours...
>
> They later sent a bill for 20k to my employer... which was more than I was paid
> for a year (it was 1985 I think).
>
> Whoops.

Great story. Did your career advance any further with that particular
employer..?

--
jeremy

On Wednesday, 17 May 2023 at 14:26:04 UTC+1, jeremy wrote:
> On 18 Apr 2023 at 20:21:42 BST, "Stephen Packer" <stephen...@gmail.com>
> wrote:
<snip>

> > Whoops.
> Great story. Did your career advance any further with that particular
> employer..?

Well enough. I think I spent another four or five years with them (and they
sponsored me through an HNC) before I moved onto someone that
would sponsor me through a degree.

Frankly I was fucked by the salesman's promises and a poor pre-installation
survey. The sales director was an ex-radio fitter so had some sympathy
with my predicament (so didn't hang all the blame on me but instead
blamed whoever did the pre-installation survey and that wasn't me).