Do I need to Earth a metalclad back box?

[ebee]

Personally I don`t like relying on screw to fixed lug ensuring earth continuity (they can be loose or even replaced with nylon screws would you believe)
An earthing tail should be at least the same size as cpc which on a radilal 2.5/1.5 wopuld make 1.5 tail OK but on a ring would require 4.0 or two 1.5 as cpc is now 1.5 x 2.
Actually if you connect one cpc to socket, the other one to the box and link between this solves the problem and (if screw is tight) gives a little extra protection as if two seperate earth terminals as yo do if using IT equipment

 

[plugwash]

i don't see how using a 1.5mm link to connect to the socket is any worse than putting in a spur using T&E with a 1.5mm earth.

 

[ebee]

Neither do I , it`s just those "in the know" go on about reducing cpc`s

 

[PompeySparks]

I see where you are coming from ebee but I have always used a 1.5mm cpc to earth metal backboxes. The fault current you are talking about would only occur if both live phase legs of the ring touched the backbox simultaneously!