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Re: under gravel heating

Charles Chua aksed about using a new heating cable:

> Hello all, I have recently bought an under gravel heating
> cable. but the
> instruction box don't say anything about using a
> transformer at all.
> Just a plug at the end of the heating cable . Does that
> mean I just plug
> it in to the wall outlet?  Do I leave it on all the time?

The answer is, it depends.  Some cables are made to run on
a low voltage, so a transformer is used to step the
household voltage at your wall outlet down to the lower
voltage the cable requires.  Some cables run on household

Assuming your cable came from a reputable manufacturer, the
voltage requirements and watts or amperage used by the unit
should be printed on the box and on the device itself.  If
not, you shoul dhave some doubts about the worth of the
manufacturer, imo.  If it isn't printed on the wrapper,
box, or device, contact the manufacturer or at least the
vendor and find out -- in fact, get it in writing if you
can.  (Short of that you can use a multimeter to measure
the resistance of the cable and calculate the intended
voltage -- but you probably shouldn't bother with that if
you aren't used to that sort of measuring device.)  If the
device has standard plug that fits the wall socket, it
probably was intended to be plugged into household voltage.

If you plug it directly into the wall socket it will run as
long as the socket has power.  If your tank needs to have
heat added constantly, and the heater gives off just the
amount of heat your tank needs, then that will work out
fine.  But if your tank does not need to have heat
constantly added then you have two choices.

One is to plug the unit into a timer that only allows the
heater to run for a limited amount of time.  How much time?
 Depends on how much heat your tank needs and how much heat
the cables give off.  And you have tw3o choices about
timing-- one is to run the heater for so many hours
straight each day -- the number of hours on vs off depend
on what it takes to maintain your desired aquarim
temperature.  The second timing choice is to run the heater
in short on/off cycles of roughly 15 minutes, with the
length of either cycle determined by what it takes to get
your aquarium to reach and hold a desired temperature.

Alternatively, you can plug the unit into a
thermostatically controlled switch such manufactured by
Ranco, Oto, Ultralife, Jalli, and others.  These vary
widely in price and quality, with the Ranco being the best
of the lot.  The Ranco, fully wired, is also sold, by
Aqualogic and a number of other companies under their own
name.  You would set the thermostat to the desired tank
temperature, place the sensor probe into the aquarium, plug
the heater into the controller and plug the controller into
the wall socket.  Now the heater will run only when the
tank temperature is below the desired temperature.  Note
that some thermostatic controls require different steps for
set up.

With all electrical devices, be sure to read the warnings,
instructions, and safety tips that come with the unit. 
Remember that water will conduct electricity to you if
there are any leaks -- to reduce the possibility of shock,
plug your heater, or it's timer or thermostatic controller
into a GFCI wall socket.  If you do not know if you have a
GFCI wall socket, contact an electrician to find out.

GFCIs can be installed easily, but if you are at all not
comfortable doing electricalwork or have no training do
such work, you should probably leave it to an electrician. 
Your house, your life, and that of your family is worth
more than what even the best electrician charges.

Hope that helps,
Scott H.

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