Download Digital Timers and Dimmer Switches

Digital Timers and Dimmer Switches
Fire Safety Precautions
Digital Timers may cause problems when used with a low energy lamp. This
depends on how the timer switches its load on and off. If it uses a relay
(electromagnetic switch) it should be fine. Problems may arise, however, if it uses a
triode alternating current switch (triac) or a power transistor (A heavy-duty transistor
designed for power-amplifier and power-control service).
The solution is to use a mechanical timer; these are still available and inexpensive.
People need to be careful when using plug-in timers with regard to the size of the
load they are switching. For example a fridge; the load may be high at start up due
to a compressor kicking in, then when running the load is low. Manufacturers
suggest that you minimise the load using a correction factor. For example, if the
switch is rated at 10 amps, then you may only be able to connect a motor load of 5
amps to allow for the extra load at start up. There is positive evidence that fires
originate as a result of arcing at the switching contacts within the timer.
Similarly, presently you cannot use a dimmer switch with most low energy lamps.
Older style dimmer switches used a rheostat (variable resistor) to alter current. This
generated a lot of heat (was warm to the touch) but was relatively simple in design
and safe. Modern dimmer switches use electronics to change the AC sine wave to
change the voltage. In effect the light bulb switches off around 120 times per
second, when voltage climbs to a certain level it turns the bulb back on. The
Alternating current (AC) sine wave is chopped up, but so fast that it is
indistinguishable to the observer and the light appears dim. The setting on the
dimmer depends on where, on the sine wave, the switching effect operates. In short,
the circuitry in the dimmer limits the current of the low energy lamp.
In summary; any internal electronics will generate heat. A switch will be rated and
simply connects or doesn’t, but clever internal sine wave clipping is, of course, a little
more sophisticated. A basic radio or lamp should be fine; however, fridges,
compressors (varying load items) etc could be a problem. For lighting, providing the
lighting circuit (the secondary circuit – from the fuse board to the load) does not
exceed 1200W and 6A there should be no problem. Of course, if you are in any
doubts with any electrical matters you must contact a qualified electrician.