Why did my lighting circuit trip?

[John Rumm]

+1

[Dave Plowman (News)]

I've seen lots of such installations in broadcasting facilities. BBC, for example. Non of them use final circuit rings.

[The Natural Philosopher]

oh no. we simply put in a 100mA trip and rcbos on the rest.

Then we blew the 60A main wire link fuse..

So we upped that to 100A, and that took us to the next building. Still was a bit crazy with all those CRTS coming on at once after a power fail, so we had a guy on the board bringing them up in rings at a time.

[The Natural Philosopher]

I wouldn't hold the BBC up as an exemplar of anything these days.

Did they wire it with all male sockets?

[John Rumm]

Well quite possibly, but so what?

Ring circuits are less commonly used in commercial installations which tend toward using lots of much smaller radials to allow for better fault discrimination and fewer side effects on a trip.

However to infer from this that the circuit topology itself is in some way inherently less likely to suffer a RCD trip due to high earth leakage would not follow.

As pointed out elsewhere, circuits that are designed for high earth leakage situations (where "high" means >= 10mA) - need as a minimum the CPC connected as a ring, even if the rest of the circuit is a radial.

[Andy Champ]

We have a test lab with some hundreds of consumer devices (mainly DVD players) in it.

We had to get a board built with timers to bring them up a batch at a time after a power fail.

Andy

[The Natural Philosopher]

serendipitously, my RCD tripped when SWMBO was fiddling around with an extension lead.

And wouldn't come back.. so I did a phased restart of the house.

Then I went upstairs and shook the extension lead (6 way adapter) and heard a suspicious rattling.

So I took a screwdriver to it.

It was the screw that was supposed to hold the earth lead in. That was waving free and had suspicious arc burns on it where it was lying across the live..

I thought about it, and realised it had the cable it came with. Must have been like that for years...with no earth at all..