What rcd box for old wiring 30ma or 100ma asnd wherefrom?

Question

In my house there's an old grey RCD box with no writing on it which I cannot identify which has been inserted before the old fuseboard many years ago.

The test switch doesnt work but it does trip on faults. It's very dusty from the old lime plaster above it.

So What to replace it with?

I guess a 100amp RCD box with 100ma trip current.. Or should I try a 30ma trip current one, and be prepared for more trips?

I have a second 2007 consumer unit which powers a few sockets which power my computers and electric heaters etc so a trip on the old wiring circuit isnt that catastrophic..

(I've also bought a Wylex REC2S 100A 2 pole isolator (from Gil-lec). as recomended here which will go after or before the meter and before the old and new circuits)

meow2222 · Accepted Answer

Why do you want to replace one that works?NT

John Rumm · Answer

What are you seeking to protect? If you want adequate protection from electrocution then you need a 30mA device. A 100mA device is only really designed to protect the installation ins situations where the earth loop impedance is too high to reliable trip MCBs etc.

You could also say, if the old wiring is leaky enough to trip a RCD then it needs fixing anyway.

dicegeorge · Answer

ok, thanks, so i get a 30ma RCD boxand put it before all the old fuse boxesand if one of them trips often I pull out it's fuse andinvestigate,further.Perhaps this:Wylex Garage Board 2 Way 63a 30mA RCD Metal the plastic version, for a tenner more)and in it two these:Wylex MCB SP 1 Module 40A 6kA =A0 =A0 =A0 =A0|=A0 =A0 =A0 =A0|=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D==3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D/

meow2222 · Answer

fraid that wont work. Pull the fuse and N&E are still connected.NT

George (dicegeorge) · Answer

I will turn off the new isolator as well so I should be out of danger,

Bu yes, if there is a leakage from N to E even pulling out the live of that circuit would mean the RCD will still trip out, if i understand it correctly.

With lots of things (computers etc) leaking a few m.amp each the cumulative leakage can trip the RCD: I havent yet got a way of measuring each circuits leakage.

[g]

John Rumm · Answer

Depending on the actual nature of the fault that may or may not clear the trip.

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on whether you want one RCD protecting all the circuits. (given this is a second CU that may be less of a problem)

Not required unless you are TT

What rcd box for old wiring 30ma or 100ma asnd wherefrom?

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