[quote="ANDREW KNOX"]I have plastic patress boxes in stud wall; can I change the sockets with metal ones.??
If the existing r cavity dry lining boxes , then metal
can be used , with noggins of wood for support.
If metal face plate sockets r used then it is vital
that they r properly earthed to the c.p,c of the ring main circuit
Perhaps my question should have been: How do I ensure that metal socket plates are earthed correctly. Yes, they are dry lining plastic boxes set in the plasterboard so there's no earthing point in the corner like with metal boxes.
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.
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