Spooky DII (yes DII)

[Jeff Gaines]

It has RCDs on the 2 x ring main circuits and fuse cartridges on the rest. I may look at changing the fuses for RCDs at some stage.

[John Rumm]

You say RCD - but unless it is a very modern CU it is unusual to find a RCD per circuit[1]. You would typically have one RCD covering a number of circuits, with each circuit having a MCB.

Compare:

[1] You can get devices that combine a RCD and a MCB - these are called RCBO (Residual Current circuit breaker with Overload protection).

Sometimes cartridge fuses were preferred for lighting circuits since the cartridge fuse is typically less likely to trip on the current surge that can occur when a filament lamp fails. Modern lamps don't have the problem. (and you could mitigate it by using type C[2] MCBs rather than normal type B devices)

[2] Type C have the same thermal trip mechanism as B, but a higher instantaneous "magnetic" trip response. They are used for applications where you might expect higher inrush current.

[The Natural Philosopher]

[Jeff Gaines]

I guess it's one of the other. When I replaced the hall stat the neutral touched the earth and the ring tripped even though the stat was on the boiler circuit so whatever it is it's sensitive!

[The Natural Philosopher]

A neutral earth short can trip an RCD/RCBO anywhere in the system. Unlikely to trip an MCB tho

[Jeff Layman]

I had a Memera 2000 replaced by a modern CU 10 years ago. I still have a boxful of mixed MCBs (and a couple of RCDs) for it if you ever need any.

[Andrew]

The upstairs 1.0 T&E wiring in my 1976 semi was exuding green goo about 10 years ago ago I replaced it. The ground floor lighting cable seems ok. All the power circuit cable has been replaced when I changed the single ring main to

2 circuits supplying *front* of house, up and down and rear bedrooms plus kitchen and top landing.

Is there anything in the regs that says I cannot do this ?

[Andrew]

My upstairs lighting cable developed green goo exudation in 2009 when it was 34 years old.

[Animal]

the 20 year claim was way off.

that means there are problems, it does not mean the cable is failing, and it is unlikely to be failing cable at fault.

in some cases yes, in some no.

[Animal]

You have officially time travelled Green goo is usually the result of an unsatisfactory corrosive environment, not something to blame on the cable.

[John Walliker]

My experience suggests the opposite. Two cables under the upstairs landing floor at home, probably of similar vintage in roughly the same location . One developed green goo while the other is perfect.

John

[John Rumm]

There were some known batches of cable of a certain vintage that were particularly prone to it - regardless of atmosphere.