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I couldn't find anything searching on the internet, I suspect it's either because the question is so stupid it doesn't warrant an answer... But I don't know whether it's obviously not a problem or obviously crazy dangerous and you would never attempt it... But I thought I would ask the world and hoped I could get a gracious answer.

I work on a remote site with untrained technicians. As such I come across things that are clearly not to code but a lot of times we don't really have a choice and need a result with limited resources. and there is no code here ;-) I just want to keep everyone safe and breathing.

Today my electrician was wiring current transformers using CAT5 cable. And it occurred to me that that cable is not intended for 240 volt mains power, but it also occurred to me that for CT application the fact that they are twisted would be good. So it seems like a reasonable impulse on his part. I also considered the three phases interfering with each other within the same bundle of cables. But this is proper electrical engineering business and I'm just a sparky. Any advice greatly appreciated.

In general as well is it okay to use CAT5 for low current mains voltage loads. it is common here to see led household lights, and other low current devices powered by using CAT5 cables. My gut says it is just copper so as long as the current is low enough there is no harm.

Tim Williams
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chris alyui
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  • To be clear, are they connecting mains voltage directly to CAT5? Are the branches fused, and if so, to what amperage? Or only CTs? And on the CTs, what are they connected to, what voltage, or burden resistance, etc.? – Tim Williams Jun 30 '22 at 01:46

4 Answers4

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I read the title and yelled aloud "WHAT? NOOOOOO!". However it's not as bad as it appears:

According to wikipedia, cat 5 is rated for a max DC voltage of 125V DC.

https://en.wikipedia.org/wiki/Category_5_cable#Characteristics

And your application of connecting current transformers is a) isolated from the line and b) somewhat lower than line voltage. I wouldn't outright approve, but I think with careful analysis in situ you could get away with it.

And code? Probably not.

Bryan
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A current transformer provides isolation between the circuit you are measuring and the output of the current transformer, so you should not have line voltage on the cat 5 cable if it is used between the current transformers and the measuring equipment.

Peter Bennett
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CAT 5 cable is normally CL2 listed for fire and 150Vac rating.

The only problems that I've had with 50 mV current shunts and 10 kA arc welding (Zirc-Stl) using STP cable were noise glitches. These were resolved with cable orientation at right angles from the power path.

Tony Stewart EE75
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CTs installed around inslated conductors and not inside the enclosure there the conductors are terminated should qualify as SELV, and CAT5 is fine for that.

Cross-talk between CAT5 pairs at 50Hz or even 50kHz will be minimal.

Jasen Слава Україні
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