When is it time to call an electrician?

Resetting circuit breakers or changing fuses too often: could indicate that your circuits are drawing more current then they can safely provide.  It could also indicate a more dangerous fault in one or more circuits that needs immediate attention.

Turning on your air conditioner and the lights dim in the room: Motor driven appliances generally draw more current and should be wired on dedicated circuits.  This could also indicate that the amp of the line needs to be updated. 

When there is an audible buzzing or humming sounds: When the integrity of your electrical system becomes compromised, gaps appear in the system.  As the electricity fills the gaps its jumps across the gap which creates an electrical noise in the form of humming or buzzing.  Schedule an inspection as soon as possible.

When outlets, switches or other electrical- system surfaces warm to the touch: If your home was built of wired between 1965 - 1975 it may have aluminium wiring which need to be serviced regularly.  Many warning signs can also indication that smalls amounts of electricity is escaping,  which could create a serious fire hazard and burn risk or it could simply be to much demand on the circuit or something far more complicated and dangerous.