I have recently moved into a house and need to cross bond all the
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 '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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