I have recently moved into a house and need to cross bond all the pipes etc. the guy who lived here before was a bit of a bodge up artist and there seems to be no effective earth near the consumer unit. an electrician has advised me that by clamping the main supply cable, a good earth can be acheived.has anybody else done this or something similar? any advice gratefully received.
The outer armoured casing of you're mains supply is a good earth don't forget to crossbond with water and gas incoming pipes.Make sure armour is clean remove rust etc.
The 'electricity' company should provide the earth connection, connected to the main earth terminal in the consumer unit or maybe to an external earthing block.
If there isn't an obvious earth connection from the supply side then it *might* indicate that you have a TT system where it is your responsibility to provide an earth in the form of an earth rod or similar. In this case you should have a 'whole system' RCD (for current regulations this would be a 100mA time delayed on but older installations might have a 30mA one). A TT installation is likely only in rural locations.
If you have the commoner TN-S (older property, separate earth from supplier) or TN-C-S (newer property usually, earth is the supply neutral, also called PME) then your supplier really should be providing the earth connection. Give them a call and ask about it. (Note; a TN-S or TN-C-S system might still have a 'whole installation' RCD, that isn't necessarily indicative of the type of earthing)
thanks for the advice. i actually contacted london electricity yesterday who then redirected me to n power(my supplier) who then redirected me to another company who then redirected me back to.......london electricity! about 10 phone calls later after speaking to a manager i was told than earthing provision was definitely my responsibility and that was that. i will therefore clamp the sheath of the main supply and cross bond with the water and gas pipes using 16mm, but,I will get an electician to fit an rcd next to the consumer unit as this is probably beyond my scope.does anybody have any idea how much this should cost? and any drawbacks?
I'm surprised that it *isn't* the responsibility of the 'electricity company', I suspect they may be just avoiding cost but anyway that's up to you (and avoidance of hassle etc.).
You do really need to know what sort of system you are going to end up with as the earthing and RCD requirements are different. I'm sure there is a requirement on the supply company to tell you what sort of suppy you have as otherwise it would be impossible to wire correctly to regulations. They must also tell you what the maximum possible fault current is and other things like that.
If you use the sheath of the main suppy as your earth and it's separate from the incoming neutral (i.e. the incomer is two core inside the sheath) then you have a TN-S supply. First you need to make *very* sure that the sheath is actually a proper earth and connected back to the local transformer or whatever. It *could* just be a protective sheath. If it checks out OK then you don't need a 'whole installation' RCD and, in fact, it introduces some disadvantages. Only socket circuits, outside circuits and some others need RCD (fast, 30mA) protection (see other threads).
If the sheath of the incomer is also your neutral connection then you have a TN-C-S (or PME) supply. In the same way as for TN-C-S you don't need a whole installation RCD. The only real difference from TN-S is that the earth bonding requirements are somewhat more stringent.
The only case that requires a whole installation RCD is where you have a TT system, that is one where you provide your own earth rod. In this case you have a 100mA time delayed RCD protecting the whole system (this is for cable protection) and 30mA 'fast' RCD protection for socket and other circuits (to give personal shock preotection).
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