Is Zs relevant for lights

I've just installed some lights in my bedroom.  They are LEDs with no earth connection and yet the installation certificate requires me to fill in Zs.   There can be no LE shot without and earth.  Is this a relevant parameter?

  • Yes, if the cables are damaged or cut, the CPC would allow ADS to work. So irrespective of whether the CPC is used at the fittings it still needs to be continuous electrically to protect the cables. 

  • Unless the cable fitted to the light at manufacture is 2 core - as you may find on a table lamp. Even then from the point it joins the main fixed wiring, be that a plug and socket, a ceiling rose, or a joint box or other connector, there should  be a CPC, at least in UK wiring regs.

    It is only there for faults or if the device gets changed for an earthed one at a later date.
    Mike.