How To Identify Wires?

[Uncle Vernon]

I just assumed MEN systems just connected neutral to earth at the street transformer level, but doing so just before the meter box makes sense. The earth and neutral wires inside your home are separated though so the RCD systems can work.

It's not something everyone Will encounter day to day more one for the electricians. But an understanding of what is going on never hurts.

Speaking of which, don't always assume they will save you especially if they haven't been checked in a while. We had some work done on our house recently and the electrician found one of our RCDs was taking 3 times longer to trip than the minimum standard. When he replaced it, it kept tripping as we had a small neutral to earth current leak on a lighting circuit...

too true and it's not just faulty RCDs, any RCD is only as good as it's points of reference, soggy earths and neutrals place havoc with their effective trip points. While I'm a real fan of RCDs (legislated or optional) I'll be the first recommend they not be assumed to provide absolute safety.
In our crazy over legislated "protect us from thy selves" environment RCDs are mandatory for all GPOs in new works. At the same time, type approval is being given to no name 3KA rated devices of  dubious origin which may or may not have undergone any form of compliance testing our side of the pond. You can guess what is being used in many shiny fronted developer build structures so I'll always be sure to not put too much reliance on being saved by protective devices.

[vk6zgo]

An AVO Model 8 on the 1000volt ac range connected between Active & Earth is a good tester for RCDs.

Many moons ago,the Sparkies came in & installed an RCD on the workbench while I wasn't around.

I had been working on a bit of  faulty tube equipment.
My usual habit was to check the incoming mains by hanging the AVO between Active & Earth,& Neutral & Earth in turn,rather than test across Active & Neutral,as it was more convenient to just poke around with one probe,with the other lead securely clipped to Earth.

Imagine my surprise,when the whole bench turned off!
There I was,scratching my head trying to figure out what could be wrong with the AVO to make what I thought was a new Circuit Breaker drop out.
All was revealed when I took a closer look at the "Circuit Breaker"!

That was my introduction to the wonderful world of RCDs!

VK6ZGO