RobertL wrote:

I have two related questions about the earth conductor in household
wiring.

1) in my 1960s house, most of the ring main has multistrand earth
conductor; it looks as if it has the same x-sectional area as the L
and N. However, one part (added later) uses cable with only a single
strand earth. the L and N seem to be the same area (2.5 sqmm).

If a house uses a mixtrure of earth sizes does this not mess up a ring
conductivity test? The expected earth resistance cannot be calculated
properly so how can it be checked?

You can do simple checks for continuity, and also check that it is not
unexpectedly high, but that is about the limit for simple end to end
tests on the ring.

For serious testing, an earth loop tester is required. This plugs into a
socket position and tests the complete loop impedance including all the
wiring involved upto to that point. It will also let you assess the
maximum prospective fault current at each socket. Once you have results
from those tests, you can calculate the minimum size of earth wire
required to cope with the prospective fault currents - and check that
you do in fact have that in place for the circuit (otherwise you run the
risk of having the circuit fuse being protected by the wiring and not
the other way round!)

2) The cooker to wall outlet uses a 6 sqmm cable. the L and N are
multistrand but the earth is a single strand. The cable came from
Homebase and was sold for the purpose. Surely in an appliance cable
should have multistrand earth to avoid fractures due to repeated
flexing. the cooker is regularly pulled out for cleaning etc.

It sounds like you have flat twin and earth cable rather than flex. If
this is the case then even the stranded bit will only have relatively
few strands, and it is not intended to be as flexible as a "flex" - but
just easier to route and bend than if it had solid conductors of that size.

Have a look at the sizes chart he

http://wiki.diyfaq.org.uk/index.php?...es#Cable_Sizes

see if that matches your cable.

Nobody seems to sell 6sqmm cable designed for flexing (currys comet
homebase bnQ). is it really normal to use "single strand earth" cable
for a cooker?

It can be difficult to find large CSA flex, and hence it is quite
"normal" (although not ideal) to find cookers connected with T&E. Unless
you are pulling it in and out weekly then it is unlikely to be a problem.



--
Cheers,

John.

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