Replacement Dimmer Switch - wiring question

[Iggifer]

Luckily it was an MCB installation, that tripped fast enough to save the dimmer circuitry. If you had a Rewireable fuse instead, the dimmer circuitry may have been wrecked by the sudden current surge.

Have you looked at the trip curves for a 60898 vs a 3036 recently?

 

[ban-all-sheds]

Chances are if the rose is ok, the earth is ok,

Chances are?

If the cpc in that cable is connected to anything, that thing could be live when the switch is off.

but I wouldn't want to risk it

Unquestionably not.

The person who fitted that was a dangerous idiot. You should probably assume that they have done other equally dangerous things elsewhere in your house. Get the whole place checked by a competent electrician ASAP.