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Topic Title: Earthing
Topic Summary: Earthing an old lighting circuit
Created On: 25 September 2012 01:51 PM
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 25 September 2012 01:51 PM
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ebanner

Posts: 48
Joined: 18 January 2003

Can anyone help me.
I want to put a new light+fan in my bedroom. The existing wiring has no earth but light+fan needs earth. I was considering running an earth wire and attaching it to the cold water tank copper pipes. Or I thought I could run an earth wire to the consumer unit. The wire I was going to use was 1.5mm^2 green/yellow and it would be out on its own running beside the existing wiring as much as possible.
The existing wiring is from 1964 when the house was built. I don't want to rewire the whole circuit and I've been told PVC wiring goes on forever so no need to replace,

Edward
 25 September 2012 03:48 PM
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daveparry1

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Don't earth it to the water pipes! Use the other method you mentioned, earth cable back to the consumer unit, this should be 4.00mm if not mechanically protected,

Dave.
 25 September 2012 04:30 PM
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Legh

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It would be cheaper and less messy if you used a class II fan.

Legh

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 26 September 2012 09:59 AM
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ebanner

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Thanks Dave

Is this 4mm dia cable. This won't screw into the light+fan so I would have to use a terminal block to change over to a smaller wire. Would that be ok.

Edward
 26 September 2012 10:13 AM
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daveparry1

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No it's not 4mm diameter Ed, it's 4mm csa (cross sectional area) which is much smaller then 4mm diameter, just ask for 4mm earth cable at your wholesalers/suppliers,

Dave.
 26 September 2012 10:44 AM
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jsa986

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Originally posted by: ebanner

I've been told PVC wiring goes on forever so no need to replace,



Edward


Not sure why you have been told that and I would not agree with that sweeping statement. If your wiring a 4mm earth back to the board anyway, why not just replace the lighting circuit cable for twin and earth and do it properly. Your already re wiring it with a 4mm earth, just re wire it with a twin and earth.

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 26 September 2012 12:49 PM
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spinlondon

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PVC wiring has a life expectancy of about 25 years.
 26 September 2012 01:08 PM
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ebanner

Posts: 48
Joined: 18 January 2003

Having discussed with a building services manager and few other people, the main reason for rewiring if you are using the old vitrol wire. This was used before PVC came in I think probably upto the late 50s early 60s. This type of insulation really does decay but PVC I am told would last at least 100 years

Edward
 26 September 2012 02:12 PM
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daveparry1

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Agreed Ed, although I wouldn't go as far as 100 years i'd certainly say 50 years for pvc providing the cables haven't been run continuously way above their rating or in places where they've been damaged by heat or other external influences, eg chemical attack etc.
25 years would be more applicable to the old rubber insulated cables although I have seen many of those that are in excellent condition at well over 50 years old,

Dave.
 26 September 2012 02:16 PM
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rutts

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As said, bit of sweeping statement, 100yrs!! To confirm the condition it'd have to be tested. Cable of that age will probably be ok. as mentioned though if you're running the 4mm why not just re-wire with T+E? going forward you couldn't fit class one (metal) switches either.
 26 September 2012 02:37 PM
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Legh

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Originally posted by: spinlondon

PVC wiring has a life expectancy of about 25 years.


One of the authorizing bodies, NICEIC, ECA or the like, has a property they have monitored since the late 1940's that has shown that the PVC insulation which has not been unduly stressed is not showing signs of deterioration. That would be 60+ years !

The jury is still out on the life expectancy of PVC used for electrical wiring.

Legh

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Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 27 September 2012 03:24 PM
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ebanner

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The light I am wiring to is not the first one on the circuit so would have to wire more than one light. I am just trying to avoid work basically. I rewired another house before and no the amount of work involved pulling up floor boards etc.

The light+fan I got is a cheap one from Homebase for £15!

Some of the light switches have worn out so I have replaced them. I have observed when unscrewing the old light switches the standards that were in use around 1964. They didn't use metal boxes behind the switch, just a small wooden batten frame. The mounting screws go into the battens so this is how they are insulated which is probably why they didn't earth lights then.
 27 September 2012 03:46 PM
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ebee

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And later on they also used metal boxes with insulating lugs so the screws holding the switchplate in place were insulated from the metal back boxes and hence would not become live even if the backbox had .
Providing the back box was surrounded by plaster etc then you`d probably never know so long as the plaster was bone dry, if it became damp you might suffer from "Lektrik Wall Syndrome" (it tingles when you touch it!)

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 27 September 2012 09:01 PM
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antric2

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The light I am wiring to is not the first one on the circuit so would have to wire more than one light. I am just trying to avoid work basically. I rewired another house before and no the amount of work involved pulling up floor boards etc.


Evening all,
As has been suggested,if you are running a cpc cable back to the board then you might as well run a T&E 1,5mm up to the loft.
But,as you say it isnt the first light in the loop so,
run the 1.5mm into a wpbox and use wago connections or get a 60A Junction box and feed off this (60A seems like overkill but the terminals are big and can take about 7 cables and have 3 terminal securing screws each terminal).

Because the j boxes are the supply feed you then run a cable from this box to your light point.You then isolate and make redundant the old light point and use the new live supply with the old switch cable.
You then renew each light pendant point in turn without disrupting your lighting.
You are creating a ' star ' feed system and not a traditional loop.
Regards
Antric
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