Heat Tape + Foil Tape = Dangerous Inductance

[adamfritzsche]

So I have built several racks and have built several for others and this is the first time I have noticed this. I, like most use foil tape to hold the heat tape in place. I was finishing one of my racks today and had it all plugged in. I had to reach to the back of it and in the mean time shocked the crap out of myself.

At first I thought, great I have a short somewhere, but then I realized that all of the heat tape with foil on them do this.

With the herpstat on full blast, and putting a multimeter across the two pieces of tape, this is what I get.



I thought I would put that out there to serve as warning, and to ask what other tapes that people out there may use as alternatives. As clearly, conductive tape is probably not a good choice and is most likely a disaster waiting to happen.

[kylearmbar]

Don't you cover the exposed part of the wire with electrical tape? The rest is covered in plastic so I don't know how that is happenening. I right now am using heat cable, though I'll be going to flexwatt shortly.

[adamfritzsche]

Yeah, the exposed ends are all sealed off. Well, in short, this happens because AC has a magnetic field. When you interrupt this magnetic field with a conductive material, such as aluminum tape, you create inductance.

So the easiest way to remove the problem is to remove the tape and use a non-conductive one, which sounds easy, but I think if you use something like duct tape, the tubs will not slide very well. Not to mention, the duct tape will never come off the heat tape, if you ever have a reason to. So just trying to find out what else is out there that people are using.

[OsirisRa32]

how about that black electrical/electricians tape?!

[sho220]

I've used foil tape and flexwatt on a few different racks and an incubator and have never been shocked...

[adamfritzsche]

Yeah, i thought about using that, but I was unsure how well it would stick, and if they made it in anything wider than the 3/4"

[creatism]

I use clear packing tape and have never had this issue! I've never actually used the aluminum foil tape.


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[adamfritzsche]

I've used foil tape and flexwatt on a few different racks and an incubator and have never been shocked...

I originally thought about this myself, being this is the first time I have any problems. The only thing that I can think of is that the thermostat was on full power at the time, since the heat tape was at ambient temps.

I measured the voltages of my other racks and most of them are showing about 20V across the foil tape, and according to the herpstat are only putting out 30%ish power, so I am guessing that because the heat tape rarely has full power to it, this is why I have never noticed it.

[OhhWatALoser]

100 volts seems a little high, im around plenty of 480v circuits twirling next to each other almost daily, sometimes for hundreds of feet. Which yes they create enough inductance to set a tick tracer off, but 3 volts is the most I have measured. getting 100 volts induced in a couple feet, running in a straight line? I can buy some foil tape tomorrow and do my own test, but I find it extremely hard to believe it is inducing that much. A bad connection to the heat tape would easily do that though.

With that said I did always think foil tape was a ridiculous thing to use, but it seems to be very well established in the rack making world. I use duct tape myself, never had an issue.

*edit*

I'll try to remember to buy some tape tomorrow, after reading your last comment, interesting you are even getting 20v. I'll report what I get.

[dillan2020]

I noticed a few times while soldering up some heat tape the rosin core boiled out of the solder and spit around. where it landed it left tiny little burns in the heat tape. and when I put that piece in like usual thinking the tiny little pin hole would be fine it shocked me. if you soldered your tape I would bet money that is where your short is coming from and the reason your getting shocked by it.