Electrical Earth

[Matheous]

I recently moved house and have came across some dodgy wiring in the garage eg. live & neutral to a one-way light switch with the earth cut back......Can I correct this as a DIY exercise -I am connecting a metal halogen light fitting which MUST be earthed???

[coffeeboy]

By law a qualified electrician must do the work

[buildersmate]

Not true.
Part P of the Building Regs requires that certain electrical work is either done by an electrician who can self-certify the quality of what has been done or a Building Regs application is made by the DIYer, and it is then inspected.
But modification of a single circuit in this location would not normally fall within Part P anyway.
Where a light has just a hanging pendent, the earth wire should have been terminated at the ceiling rose and there is a terminal for this purpose. The cable that runs down and back from the ceiling rose to the light switch should extend the earth connection into the light switch housing but again the earth connection itself is not used.
As you appreciate, M, a metal-clad light fitting must have the external case linked to the earthing terminal in the ceiling rose.
The requirement is that the work is done by a competent person. You will have to adjudge this, M.

[Matheous]

Thanks buildersmate- but can you explain how to 'create' an earth when there isn't one??......

[terence7556]

is there any spare on the cable (i am assuming it is inside the ceiling), pull it down if poss, and cut back the grey outer insulation enough to connect the earth conductor to a connector block. buy a metre of cable and cut off enough to run an earth connection to the new fitting.fit yellow/green sleeving over any exposed earth conductor

[buildersmate]

Yup, as T say. We are assuming you have twin + earth cable here - as fitted since about the 1960s.

[Matheous]

I DO have an earth connected to the new appliance -but there's b****r all at the other end which has been cut back at the light switch I want to connect it to....

[buildersmate]

We are both assuming that you can get access to the end of the cable that feeds this light. If it has conventional grey cable it will be twin core plus earth. We understand that the outer sheath has been cut back somewhat and the earth sliced away. But if you can access the cable itself the cheapest and safest way to reconnect it would be to mount a little circular 10A junction box somewhere close to the end of the old cable, connect up a short length of new cable to bridge the gap to the ceiling fitting.
Looking at the wording of your post again, you refer to the light switch. The light switch, if it mounted half-way down the wall has no bearing on the earthing system for the light at all. Look at the image on this web link (down the page). Does that help explain where the earth connection goes? - and that it is not connected through the switch
http://www.diydoctor.org.uk/projects/lights_an d_switches.htm

[Matheous]

buildersmate -The sw I want a feed from has T & E live & neutral connected to it with the earth cut back. There is a ring of strip lights around the garage rroof which seems to terminate at the switch in question. My problem is that I don't trust the previous owners wiring and need to be able to test for an earth everywhere- including the garage which is fed from a 13a CB in the house consumer unit.
Thanking you for your extensive replies buildersmate....Your help is greatly appreciated.