FYI

If the heat tape you describe is like all the rest of standard heat tapes,
the knob on the end is not a resistor. It is simply a plastic cap filled
with silicone to keep out moisture and to prevent grounding of the two
conductive wires. Most commercial heat tapes use about 3 watts per linear
foot. The material between the two conductive wires is a resistive material
which heats up as current passes between the hot and neutral. If a heat tape
is cut too long, the resistance becomes too great for the current to
overcome it and the heat tape won't heat. The better tape kits have either a
little glass fuse in the plug or it will have a reset button.

Good Luck

Dan
"T-n-T" wrote in message
...
I was wondering if anyone could help me with a design of a heat cable
for my new terrarium. I have on fairly expensive cable and would like
to duplicate it. It has a 110v plug at one end and is about 8 feet
long. The end has a small knob which I assume is a resistor of some
sort. The actual heating part of the cable is about four feet long, the
rest is just to get to the outlet. Oh yeah it is 15 watts. I think for
someone who knows how this works should be a no brainer. I recently saw
an article somewhere that suggested using a toaster or aquarium heater
element, halved , coiled around a small wire and threaded into a
silicone tube. Any advice would be excellent, thank you.

BTW, i have seen some online for planted aquariums that use a long
length of wire, which is exactly what I need but seems to be really
long.
http://www.thekrib.com/Plants/Tech/