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Re: Heating Cables

Colin Gorton asked about heating cables for 1,000 gallon tank  -- 1,000
gallons, just think of the flourite bill in a wading size tank:

Substrate cables are surely the practical energy efficient way to go. 
You don't need to go to higher than standard house voltage (110-120) to
use multiple cables if they are powered in parallel.  110-120 volts
ables are probably no more dangerous than using an electric heater
housed in a glass tube.  Low voltage (6-24 volts) is much less likely
to shock you if an electrical leak occurs under water but the
likelihood is already pretty low if you use a GFCI.  IF you go low volt
route, plan on having thermal protection against a step-down
transformer overheating (it really could start a fire) -- internal
transformer shorts create heat which melt insultaion and create more
internal shorts, etc.

A variety of cabling patterns could get you several commercial cables
in one tank, powered in parallel, without having the powercord leads be
too obtrusive.  If you make your own, you can make one cable for
whatever volts and watts you want.  You want a UL listed GFCI on the
line no matter what, anyhow.

A big (er, I meant HUGE) tank with lots of lights will get a lot of
heat from the lights and water pump(s).  You have thick glass to help
retain heat, and a large tank has a lower ratio of surface area to mass
than a smaller tank -- so that helps hold in heat more also, relatively
speaking -- you won't need 3 - 5 watts per gal -- more like 1 (or 2

All of the devices I have seen or read about for keeping pipes from
freezing were not intended to be submersed -- especially not
indefinitely.  Most of them have warnings that tell you not to submerse
them.  Will they work?  Some will.  Will they retain their watertight
integrity?  You'll have to call a bookie -- even the manufacturers
won't put odds on that bet.  

The insulation has to be able to retain it's pliability, puncture
resitance, and impermeability to water even after prolonged soaking --
lots of wire insulation won't do that.  Vinyl, for example gets a
little goofy from sitting in water -- just look at an airline that's
been submerged a while; it discolors and swells slightly.  So silicone
insulation is what is usually recommended.

Scott H.

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