Nathan said:
What causes a dimmer switch to make the lights flicker? Every time I install one this happens.
(I'm sure this question makes it very clear that I am NOT an electrician

)
-Nathan
Seveal reasons could be considered.
1. Ripple frequency injection. Used by electrical councils to control the time of use of "off Peak" devices like hot water services, floor heating etc.
2. The type of dimmer could be leading or lagging edge and not suit the lamp type installed.
3. Poor termination of conductors.
4. Dimmer is "on the way out".
5. Poor voltage supplied to your installation.
One of the above is most likely.
Cheers
Ross.