Strange looking fuse!

[securespark]

Did a replacement CU in block of flats today.

When I took out the cut-out fuse, there was no cartridge fuse in there, just a thick metal plate, bridging the contacts.

Reckoned the place would toast before that ever ruptured, so I called out the REC, who replaced it with a 100A fuse.

But when I said, the other flats may be the same, he shrugged and said "Doubt it".

If that were me, I'd have checked the lot, wouldn't you?

 

[ban-all-sheds]

But you don't work for a REC...

 

[kai]

Perhaps someone tried bridging a persistently blowing mains fuse with a metal plate?

 

[Lectrician]

I imaginge there is a ryfield sevice fuse box at the origin (belonging to the REC), with 60 or 100amp fuses with in(these have several fuses within), with all the seperate flats concentrics terminated back to here. This is where the protection is, and the link you have seen is merely the connection from concentric to tails, used when the meter requires replacement etc.

I have seen this vastly in our area.

 

[securespark]

Fair point, Lect.

But why did the Norweb geezer replace it with a fuse, then?

If your scenario is correct, will there be discrimination now there is a 100A fuse in the cutout?

 

[Lectrician]

No, there would be no discrimination

I guess the REC bloke wasn.t fully up on his facts of that install. I can't imagine any REC leaving a solid link in a carrier without realising. Very often if you call out a REC as an emergency, you get who ever is available, this could be a jointer, linesman etc, and they will only have the basic knowledge of the network, not all the ins and outs.

I have had to show a linesman how to test for a blown fuse in a substation on a sub fed site.

 

[securespark]

Guess what I can do is look at the Landlord's supply main fuse to see if it is the same..................

If it is, shall I call the REC to re-fit the link?

 

[plugwash]

nah i wouldn't worry about it

he changed a link to a fuse

there isn't really any way that can make an install less safe

 

[kai]

It's a bit like my 8 metres long 3000 watt immersion heater circuit being fed from a B16 MCB, with 2.5.sq.mm. cable to a 13amp FCU, and 1.5.sq.mm. heat proof silicone rubber flex to the immersion heater itself - No discrimination. but perfectly safe and this method of installation is allowable by BS7671:2001.

 

[ryanj]

You really like that immersion heater of yours, don't ya?

And there is discrimination, the 13amp fuse would blow way before the 16amp MCB on an overload.

 

[plugwash]

yes but on a short the 13A fuse would probablly be left untouched as the mcb fast tripped

 

[Lectrician]

Not this old line again!! - We never fit FCU's to immersions - 20amp plate switches are the way

 

[kai]

Why not? Surely an MK-K330-WHI fuse-connection unit, will enable lighter flex to be used from FCU to immersion, 1.5. instad of 2.5. sq.mm.

(Screwfix sell 2.5. flex at significantly more than 1.5. heatproof flex.).

 

[Lectrician]

If you use a 16amp breaker, and no FCU, you can still use 1.5mm flex.

The element cant overload the flex can it? It is a fixed drawn current.

 

[Damocles]

What happens when the element casing ruptures and the water shorts the element?