by ericmark »
Sat Aug 02, 2008 9:21 pm
There has been many posts about earthing of back boxes and it is considered by many not to be required as if metal they would be earthed by the 3.5 mm fixing screws. So in your case so long as the earths are connected to the socket there should be no problems.
As how to ensure earthed correctly we use a meter called an earth loop impedance tester which draws heavy current Live to earth for few milliseconds and calculates with the volt drop what the total resistance of cable from supply transformer to socket and back is and is referred to as Zs.
Because these meters are expensive and can cause danger when used they are normally only used by electricians.
Assuming on a ring main measuring between both earth wires is normally a good indication. 1.4 ohm is the maximum Zs reading considering the supply to house can be 0.35 I would consider 1 ohm between both earth wires as max.
Does this answer your question?
