Another RCD puzzler

[ARWadsworth]

I was trying to keep it simple. But you are correct a privately owned water supply can be used as an earth rod.

[John Rumm]

Its worth keeping in mind that the only earthing you have is that from the water pipe (if one treats this as the main equipotential bond to the incoming water service - its what is called "fortuitous earthing" - i.e. its a bonus, but not what the connection is there for!). Also worrying is that you don't yet know what resistance the water pipe connection is giving you.

This means you have a potentially very serious hazard until you fix it.

Any circuit on the non RCD protected side of the CU, could develop an fault to earth, and its entirely possible that all the earthed metalwork in your house will then become live at close to mains voltage, and the power will stay on! (if the water pipe is giving 25 ohms or more, then there will never be enough fault current to open any MCB on an earth fault)

Yup, you need a time delayed type for this application (usually with a S suffix in the number) - this stops the whole house getting tripped off when a fault can be cleared by the downstream RCD.

Yup. The existing earth wire can stay as a main equipotential bonding conductor. If you have gas, then you need another connection to that pipe as well on your side of the meter.

Installing an earth rod is not difficult, but you need to be able to test it after you have done so, to make sure you have an adequate installation. There are a couple of ways discussed in the following article - including one that does not require elaborate test gear:

[Dave Osborne]

[Luke]

Hi, I removed the cover from the old fuse box and found that the 10mm earth wire from the CU directly above it simply connects to the earth wire that used to feed the old electric boiler, i.e. there is no internal link between Neutral and Earth as per the photo on the Wiki. The "dark streak" up the wall is historical and predates the installation of the electric boiler, (probably pre-1997) as the cable to the electric boiler is still in place and runs in surface mounted trunking vertically up the wall to the first floor.

Definitely looks like it's a TT installation then, which ties in with what Western Power Distribution told me, that they do not supply an earth to this property.

Luke

[ARWadsworth]

> or if the above wraps.