Tonights DIY

[Dave Liquorice]

What's wrong in these pictures?

There had been a funny smell for the last few days, very similar to a dead animal (damn cat...) so not that much attention paid. Tonight noticed that the off-peak load was 3 kW down on the power consumption plot, storage heater connected via this switched fused connection unit was not powered up for some odd reason.

Looks like one end of the fuse carrier has overheated a little. New SFCU installed and all back working, checking it an hour or so later the new one is warm... I did check fuse carrier spring tensions. I guess this is just the dissipation in the fuse, it is after all carrying 13 A or as near as damn it.

The burnt out one has only been in use about 2 years as the old one was full of brick/plaster dust and the switch was dodgy. The old one was a SFCU but thinking about it now a plain SCU should be fine as each storage heater has its own 2.5 mm fixed wiring spur, 2.5 mm flex and B16 MCB in the CU. Am I correct in thinking that fuse is more of a liability than anything else?

[tony sayer]

In article , Dave Liquorice scribeth thus

That's just a fuse thats had a bit of a duff high contact resistance than it ought be, the sustained current has caused a bit of heating which made it worse and then a bit worse and then that mess;!.

It should be capable of handling its rated power continuously.. .

[Andrew Gabriel]

They're normally individually connected back to MCBs, and don't have a fused connection unit. A fuse at max load dissipates 1W which it should survive, but yours probably got some contact resistance added somehow. Anyway, the fuse isn't required with the B16 MCB.

[Brian_Gaff]

I've often taken plugs apart and found that a bad joint or whatever at one end of a fuse has caused enough heat to deform the plastic. Maybe they go kind of dry with age? Brian

[Fredxxx]

In theory there should be a gas tight contact area.

Copper doesn't creep, though I do wonder if there is a differential thermal expansion of a terminal and wire that could amount to some movement and hence loosening?

Fuses do seem to oxidise and I have no idea what they are generally coated with, or their expected contact resistance?

[Dave Liquorice]

Thanks, 1 W is enough to make things warm, which then oxidise, which increases the contact resistance, so more disipation...

Handful of 20A DP switched outlets on order.