1970s bonding requirements ?

Question

Hi guys, just after a little information for myself really. 
 I changed a consumer unit today on what is almost certainly an early 1970s install. Current set up is PME, I have no reason to doubt it was always the same. 
 16mm tails with a 10mm earth. Main fuse has been down rated to 80amps at some point. 
 Wylex wooden fusebox with no back on a block wall in the garage. No sign of there ever been any sort of RCD or voltage operated device fitted as tails are straight into the back of the fusebox. No tell tail holes. 
 The wiring is original, all copper with an earth in the lighting. 
 My question relates to the bonding. It looks like a 2.5mm was used, it is certainly only a single strand. Was this ever acceptable ? It surprised me as the way the consumer unit was wired out and the standard of the wiring behind many of the original accessories looks very good so I think done by a decent sparky. 
 I don't believe this was ever a TT installation due to the lack of any type of trip. 
 Gary

mapj1 · Accepted Answer

well how far back to go.. Bare wire suggests pre 1970, or at least an electrician following rules from pre 1970 - by 1970 earth would be solid green. 
 Realise that back then, with no internet and so on, not everyone wiring houses would have been aware of changes of rules with any particular urgency, so may well have been a few years "behind the curve" to use the modern phrase and may not have had the latest version of anything in particular to hand.. 
 Even so the metric issue of the 14th edition (1970) permits 2,5mm bonding as follows

regards Mike

mapj1 · Answer

And the table referred to note that really it relates to the phase conductor size, with a 1mm minimum. 
 for 16mm supply, 2.5mm looks about right for bonding, but not for the main earth where a little over twice that would be expected, 
 it may be finger trouble, 
 Mike

mapj1 · Answer

the previous 13th edition (1955 and 1958 updates ) 
 do not have the bonding and earthing separated out in the same way, and are given in imperial units.

0.0045 inch square is a touch under 3mm2 - and in general got metricated down to 2,5mm2 0.1 inch square is almost 65mm2, and tends to be metricated to 50mm2

1970s bonding requirements ?

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