PME Riser

[Dave Plowman (News)]

How do you remove a fuse from one of these that is well and truly stuck? Possibly welded in place? I'm a bit worried about levering with a screwdriver in case a) I break it b) hit a live terminal...

[Lurch]

On Tue, 01 May 2007 23:00:46 +0100, "Dave Plowman (News)" mused:

Ring the REC wotsit. If it comes off in several pieces I would imagine you'll have a job explaining that it 'just fell off'.

[Dave Plowman (News)]

That's what I did first thing - and they said they'd be round in a couple of hours. I left after 6 having run out of things to do - and they arrived

15 minutes later. The owner said it only took them 10 minutes to fix - although they did end up moving it to a fresh part of the wood board to get a better fixing. But he didn't see how they got it out.

[Andrew Gabriel]

c) slip and short out the supply.

When I was doing one of the C&G courses, there was a picture of an accident involving a switchfuse. A pair of electricians were to do some work on the circuit (IIRC, it was 3-phase

200A). They moved the lever down to switch off, but the lever had become disengaged from the switch mechanism and it didn't switch off. Electrician immedately realised and opened the switchfuse and levered the mechanism off with the screwdriver. He'd flicked such mechamisms many times before when assembling the switchfuses and did it without thinking, in this case without thinking it was live. The screwdriver shorted a phase to the case, resulting in an arc which almost instantly spread between the 3 phases, until the upstream protection tripped out. Both electricians were very seriouesly burned by the arc, which would have had a power in the megawatt range.

I must admit that in the head-ends I've seen, there isn't much possibility of shorting the supply from the fuse bay, but there maybe some where this is possible.

[Andy Wade]

You really don't want to do that:

[Tim Downie]

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[Clive Mitchell]

The guy who was on fire in the first clip had to be put into a controlled coma due to the severity of the burns.

I had some work colleagues badly burned when a large bit of industrial switchgear blew up. All it took was a bit of loose metal falling across busbars internally, and the resultant arc caused a total failure. The apprentice was blown clean out of the switchroom, while the spark somehow managed to get his hands over his face before being engulfed in flames.

Worse still. On one of my jobs I deal with an 800A per phase supply that is situated right through the wall from the substation that provides it. Very high prospective short circuit current. The room it's in used to be used as a canteen by the guys, but it's now classified as a substation itself for safety reasons.