[RobertL]

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?

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.

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?

thanks for any comments anyone cares to make.

Robert

[John Rumm]

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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[Lurch]

On Thu, 21 Jun 2007 01:31:00 -0700, RobertL
mused:


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?

The resistance is the restistance, no matter what the cable is.

It's either good enough or it isn't, whether it's multistrand or not.

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.

Twin and earth is designed to be used as fixed wiring cable, it is not
designed for flexible final connections technically. You want 6mm 3
core flex.

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?

No, the normal method is to use 6mm twin and earth. You won't find 6mm
3 core flex in any DIY stores.

How many times is it removed this cooker? Unless you're removing daily
I can't see you're going to hit a problem.
--
Regards,
Stuart.

[RobertL]

On Jun 21, 11:14 am, Lurch wrote:
On Thu, 21 Jun 2007 01:31:00 -0700, RobertL
mused:



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?

The resistance is the restistance, no matter what the cable is.

It's either good enough or it isn't, whether it's multistrand or not.

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.

Twin and earth is designed to be used as fixed wiring cable, it is not
designed for flexible final connections technically. You want 6mm 3
core flex.

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?

No, the normal method is to use 6mm twin and earth. You won't find 6mm
3 core flex in any DIY stores.

How many times is it removed this cooker? Unless you're removing daily
I can't see you're going to hit a problem.
--
Regards,
Stuart.


thank you for your comments gents. the cooker will come out once a
month I guess so maybe the existing cable is OK.

Also thanks for comments on earth resistence. I will get the rings
checked when I have the CU changed for one with RCDs. that will eb a
pro job not DIY of course.

Robert

[Dave Plowman (News)]

In article . com,
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.

It will likely be 7/0.29" strands for the line and neutral, and 3/0.29"
strands for the earth.

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).

Yup. That's the modern metric equivalent.

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?

The ECC size did also change with 2.5 TW&E some years ago. But only really
made a difference on very long runs unlikely to be found in most houses.
The correct way to check is with an Earth Loop tester - this basically
puts a brief pulsed short to earth and measures the current drawn. This
measures the earth as installed and checks also for poor connections.

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.

If it is a reasonable loop it will stand many removals of the cooker for
cleaning as this is the common way of attaching a cooker - although you
can buy flex from a specialist.

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?

thanks for any comments anyone cares to make.

Robert

--
*Many people quit looking for work when they find a job *

Dave Plowman London SW
To e-mail, change noise into sound.

[Alfie]

Originally Posted by RobertL

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?

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.

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?

thanks for any comments anyone cares to make.

Robert

Yes Thats normal these days.