Electrical Earthing arrangements in older properties

[mac]

What is the legal position regarding earthing arrangements for a (domestic) property that has as its main earth, a connection to the income cold *water* pipe. I know that this is not allowed by the regs (although I think it used to be?). There are several houses I know of in this suburb area that have this as the only earth. Does the use of an RCB on the CU make this acceptable or *must* it be changed?. If it has to be changed, what to? I don't know if PME is available here - if not how about earthing rods per propery? Although safety comes first of course I guess this could start to get expensive especially in that each such arrangement has to be retested/certfied by some organisation?

[Andy Wade]

AFAIK there is no legal requirement to rectify things like this. Such installations would fail a periodic electrical inspection & test though, with the need to provide a proper means of earthing flagged as urgent.

Are you sure that you are not confusing a main bonding connection to the water pipe (which is required) with the actual means of earthing - which would usually be to the lead sheath of the supply cable (TN-S system) on an old installation with underground cable feed.

PME (TN-C-S system) may be available (ask the local distribution network operator), but would require new service cables to be installed.

If the supply is overhead then it's much more likely that there is no earth. In that case the options are to add an earth electrode (TT system) and RCDs or to upgrade to PME, if available. A single RCD is no longer acceptable - there should be a 30 mA one protecting the socket circuits and a 100 mA one for everything else - see the IEE On-Site Guide for details.

[meow2222]

there are proably milions of propertes like this. As long a your water supply remains metal, its normally a non issue. Metal water pipes make excellant earths. However if the pipe upto the house is ever replaced with plastic, you've got a real problem, and the installation could become dangerous in some cases.

Simplest solution if youve got plastic water pipe is to add an earth rod and connect it to the existing earth - dont undo whats there.

NT

[meow2222]

there are proably milions of propertes like this. As long a your water supply remains metal, its normally a non issue. Metal water pipes make excellant earths. However if the pipe upto the house is ever replaced with plastic, you've got a real problem, and the installation could become dangerous in some cases.

Simplest solution if youve got plastic water pipe is to add an earth rod and connect it to the existing earth - dont undo whats there. Note that if relying on an earth rod, RCD or ELCB protection will be needed.

NT

[Fred]

The argument against relying upon a service for an earth is that the material used can be changed on a whim by the service company at any time and is not under your control.

[mac]

No the supply is overhead - looped from house to house.

At cost to consumer I presume? Fair enough, but just wondered.

Ah yes, that is the case.

One place I know the layout of :-) has split load CU with 30mA RCD of the socket rings, no RCD on the lighting circuits and appropriately rated MCB's for all circuits. Installing an earth electrode is on the cards here then - althought taking a look at the On-site guide, testing the loop impedance is fun!

thanks

[mac]

As a followup to my followup, what does the earth cable from an earth electrode normally/prefferably terminate in? Is there a large block of copper called ? - or does it usually go straight into the cu earth connector?

[Bob Mannix]

AFAICR it *has* to go straight to the CU connector without intervening connections that might work loose and be hidden. Not sure if this is a strong recommendation or law though. (I had to run a long one out of sight a while ago).

[Andy Wade]

Well it goes to the "main earth terminal" - usually one of these

but it can also be the earth bar inside the consumer unit. The main bonding conductors to water and gas etc. must go to the same terminal.