# Deicing cables

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#### KevinW

##### Member
I have a 100ft. deicing cable and would like to cut it in half.
Are these cables different gauges for different resistance?
Can I use a resistor to substitute for a shorter length of cable?

#### ronsimpson

##### Well-Known Member
I have not tried this. Wire for heating (stove heating elements) is different and you can not solder to it for several reasons.

You need to know the resistance and watts to find a resistor.
Wire is 1 ohm/foot. 100 feet=100 ohms.
Voltage is 110VAC.
Power is 100 watts.
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50 feet of wire = 50 ohms So to 1/2 the project you need to add 50 ohms using a resistor that can handle 50 watts. (so pick a 75 to 100 watt resistor)
Remember 1/2 of the total power is spread out over 50 feet and 1/2 is in a small spot (resistor).
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If you only need 50 feet, run the wire down and back. Using up all 100 feet and saving all this trouble.
RonS,

#### KevinW

##### Member
Thanks Ron;
At 50ft. I will be doubling the length of cable.
Manufacturer states the 50 and 100 foot cables "Roof & Gutter Deicing" 8 Watts per Foot at 32F, 300 watts for a fifty footer."

#### dknguyen

##### Well-Known Member
Thanks Ron;
At 50ft. I will be doubling the length of cable.
Manufacturer states the 50 and 100 foot cables "Roof & Gutter Deicing" 8 Watts per Foot at 32F, 300 watts for a fifty footer."
Is that actually a problem though? Don't you just run it for less time? Or does it just always stay on? Or is the issue you don't have a strong enough source?

#### crutschow

##### Well-Known Member
If it's 8W/ft then cutting the cable in half to 50' will double the power to 16W/ft or 800W.
(Don't know how they got 300W for a 50' cable @ 8W/ft. I calculate 400W.)

#### rjenkinsgb

##### Well-Known Member
Trace heating cable I've seen can be cut to length.
It's usually got two conventional copper conductors plus either a resistance wire that connects between the two alternately or a high resistance "membrane" element bridging the two conductors.

eg.
https://encrypted-tbn0.gstatic.com/...4d4KNzG7Dj7idQiVzYYbOSWdPBW6n0__DeyNdP4SMI78R
http://www.calorique.info/images/selfreg/Selfreg_en.jpg

If your cable has two conductors through it, cutting it will not affect the operating voltage, each section can be used independently.
At worst you get a short "dead zone" at the cut, if it's the wire element type.

If it's only a single conductor then the operating voltage is proportional to the length, for a given output-per-foot.

#### KevinW

##### Member
Is that actually a problem though? Don't you just run it for less time? Or does it just always stay on? Or is the issue you don't have a strong enough source?
It's just too long for the area I have to deice.
At fifty feet I'm already doubling the cable in the same area.
It only gets turned on when the ice starts melting and dripping for a duration of 2-3 hours at a time.
The source is 110 volts AC, no problem there.

I calculate 400W
Me too!
The 100 footer is 600 watts.
If it's only a single conductor then the operating voltage is proportional to the length, for a given output-per-foot.
How would it heat with a single conductor and no neutral?

#### ronsimpson

##### Well-Known Member
http://www.delta-therm.com/assets/in-series-roof-deicing-datasheet.pdf
I was wrong again. The wire does not heat. There is a "PTC (positive temperature coefficient) conductive polymer" that is connected between the conductors. The conductive polymer does not conduct on hot days and draws current on cold says. It tries to keep the cable at some temperature that is above freezing.

It is safe to cut the cable. (insulate the wires on the end) I now see how they get X watts/foot. Cut to any length you want.

#### dknguyen

##### Well-Known Member
How would it heat with a single conductor and no neutral?
You run it both ways away the hot back to the neutral.

#### dr pepper

##### Well-Known Member
I've just been working with some trace heating - winter checks found some bad stuff on a pipe installation.
I believe there are different kinds, some have sections, you can shorten the run but there are only certain points where you can cut the cable, the neutral must link to sections along the run, other stuff as already implied is just resistance wire, with this stuff you have to be carefull not to make the run too short or you'll overload it.
I've never heard of the stuff ron just mentioned thats interesting, I've probably only ever come across ancient installs.

#### KevinW

##### Member
Thanks for the responses, after discussing the topic I believe the wire to be resistive like nichrome.
I can cut it and test for 3 amps.
I'm trying to sell the 100 footer and put the money towards a shorter cable but if I can't sell it I won't have a use for it so I'll cut it.
Thanks again.

#### KevinW

##### Member
When you cut these cables to thirty feet you have an open condition and when shorted you get 9 ohms.
The only two options I see would be a 200 watt resistor on the end or reduced power supply to 30 volts.

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