Add light to fused spur

[mr rob]

would there be a voltage on the earth normally?
so wire from FCU to a normal switch, wire to light outside. done

 

[ban-all-sheds]

would there be a voltage on the earth normally?

There can be a voltage between your installation earth and local true earth, but nobody has suggested you measure that.

check the voltage of all terminals to earth is zero

You do have a multimeter or other 2-pole voltage tester?

 

[John D v2.0]

would there be a voltage on the earth normally?
so wire from FCU to a normal switch, wire to light outside. done

The earth is at a given voltage, we reference other potentials against that. Your supply neutral is connected to earth somewhere, so it's a good reference point to test against.
Not really a "wire" unless you're using it as a verb.
You need two wires from the fcu to the switch, ie live and earth. You need one from the switch to the light,ie switched live. You need a neutral from the fcu to the light, and you need an earth to the light from either the fcu or the switch.

 

[securespark]

It might be useful to fit a DP switch (with or without indicator) so it can be fully isolated in the event of a fault.

 

[winston1]

It might be useful to fit a DP switch (with or without indicator) so it can be fully isolated in the event of a fault.

Would you apply this logic to every light in the house?

 

[bernardgreen]

Would you apply this logic to every light in the house?

The logic applies to lamps which have a higher than acceptable risk of being affected by damp or other forms of damage. Isolation is necessary to allow other lights on the circuit to be used while waiting until the damp / damaged lamp is dried out / repaired.

 

[securespark]

No. Only lights outside.

In the event of water damage, a DP switch allows the user to isolate the faulty part of the circuit quickly and easily, allowing the rest of the circuit to be re-energised.