So what would happen if you did not have continuity back to the CU but did have an earth/CPC link between light fitting and switch?
Provided that the earth connection is sound, the lamp will light between earth and live - but not between earth and neutral. Lucia.
As a matter of interest, what's the difference with double insulated light fittings, is it simply that the cable has extra insulation.
Double Insulated
Double insulated or class 2 electrical appliances are products that have been designed in a way so as not to require a safety connection to electrical earth (These products must NOT have a safety connection to Earth).
These products are required to prevent any failure from resulting in dangerous voltage levels becoming exposed causing a shock etc. This must be done without the aid of an earthed metal casing. Ways of achieving this include double layers of insulating material or reinforced insulation protecting any live parts of the fitting.
There are also strict requirements relating to the maximum insulation resistance and leakage to any functional earth or signal connections of such appliances. Products of this type are required to be labelled "Class II", "double insulated" or bear the double insulation symbol (the symbol displayed above)
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