Aesthetically, the light switch has clearly evolved since the advent of the quick break switch, but the principles behind its operation have remained fundamentally the same. Proof, perhaps, that John Henry Holmes was an engineer of some repute, despite being less of a household name than Thomas Edison, Joseph Swan et al.
If the mechanics of the light switch haven’t changed much per se, the methods and materials employed when wiring to it certainly have. No longer will VIR and waxed cotton covered conductors protected by nothing more than a bit of fuse wire in porcelain carrier suffice as would have been the case when the light switch was in its infancy, oh no. If you want to comply with current wiring regs, which I’m guessing everyone reading this does, then there’s a good chance that today’s switch drop will require not only earthed mechanical protection, but RCD protection as well, depending on the particular characteristics of the installation. Section 522.6 of BS 7671 details these requirements in full and compliance will almost certainly result in the need for additional materials, labour and, inevitably, the costs associated with purchasing and installing them.
Having said all that, if you’d rather avoid installing earthed metallic and/or RCD protection to literally every switch drop, yet still comply with BS 7671, the afore mentioned Section 522.6 obligingly provides a means of doing so in the form of regulation 522.6.204, indent (v), which reads: