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Electrical safety

An important not for all who are toying with heating wires. A ground
fault interrupter is an excellent idea, and I wouldn't have a fish tank
without one. A GFI, however, cannot protect you from doing something
stupid like putting your water soaked hands directly across the
secondary of the transformer. In this case there is no ground fault. A
current is flowing in the secondary of the transformer and in you. The
primary  winding current is balanced and there is no fault detected.
I have been shocked by as little as 12 V and while it is usually only an
annoyance, it is potentially dangerous. It only takes 0.035 Amps to kill
a person and recent evidence is that it can happen with a far smaller
current than that.
Play safely! Turn off the power to your heating wire when you are making
or adjusting the electrical connections. Keep the wires out of harms
way. Do not pinch the wires with the hood, cover glass, canopy or
lighting fixture. If the wire becomes damaged outside the tank seal the
repair in silicon rubber. If the wire becomes damaged inside the tank,
discontinue its use or replace it.
I don't mean to be an alarmist. With a little bit of thought you can
easily put together an inexpensive and functional heater. Electricity
and water are just a dangerous combination, and a false sense of
security make them ten times more dangerous.
Harvey Schneider
<harvsch at earthlink_net>