RTD Signal interference?

[Dgonza9]

I posted yesterday about my plans to mount a control panel on an arm in the ceiling. Like this:

I was looking at running wires in the mounting "conduit" and was worried about signal interference. I was told it was a code violation to put power wires and signal wires in the same conduit. I was also told running wires in Black Iron Pipe was a "severe" code violation.

I'm changing my plans, but I'd still like to understand why it's a problem to run wires in the iron pipe and why signal and power wires can't be in the same conduit.

Is the iron pipe going to prevent heat dissipation? Why does having signal wires and power wires in the same conduit lead to a hazardous condition?

Also, what happened to my post? Was it deleted for some reason?

Cheers.

 

[audger]

im not exactly sure why running power cables thru black pipe would be against code, could have something to do with the wires possibly rubbing on the sharp threaded edges...? or maybe two threaded black pipe connections arent a sufficient ground junction.

having signal wires (especially analog) next to power wires is never a good idea. i know some people who have destroyed some expensive network gear by running unshielded Cat5 cable right along side household electrical wiring. the inductive energy in the electrical cable can create a considerable amount of stray voltage in the signal wire. its best practice to always cross an electrical cable with a signal cable at 90* angles to avoid such induction.

the hazardous condition comes in when you think your >5v signal wire is carrying low voltage, but it could actually be 10 or 20 or 50+ volts depending on how well its coupled to a nearby power cable (and how much current is traveling down that power cable). not only could it destroy whatever its plugged into, but it could zap you as well.

 

[passedpawn]

At some point one poster told another poster FU. I think that was the beginning of the end. I guess a mod just razed the thing. Your thread was collateral damage.

 

[Yuri_Rage]

At some point one poster told another poster FU. I think that was the beginning of the end. I guess a mod just razed the thing. Your thread was collateral damage.

Exactly. Sorry that had to happen. If there's a particular post you want to reference, let me know, and I'll copy the content to this thread.

 

[DaleHair]

I often have to run control cabling inside 208v and 480v gear, and even with shielded cables with only one end of the shield grounded, I still get noise and have to loop the cable through a ferrite core to reduce the noise to an acceptable level. I have also seen cat 6 wires run in a pit next to 480v wiring with no problem. It is best to just keep them seperate.

 

[Hermit]

Black pipe may be a no-no since it is specified to carry gas and that is what people EXPECT it to do. Could be something simply to avoid confusion. For example, you have an emergency that requires safety personnel to respond. I once went on a refrigeration recall where a home owner terminated a 250VAC outlet with a 125VAC receptacle. I guess the good news is that only the refrigerator died.

 

[DumpsterDave]

If you look at any conduit that is designed to cary wire, you will notice that it is all either plastic (i.e. non-conductive), or a corrosion resistant metal such as galvanized. I am not sure, but part of it may have to do with rust, weight, or as audger said, because it typically carries gas.

The reason why you typically can not run signal wires with high voltage wires is becuase "signal" wires are considered low voltage and not prone to arcing if two wires cross or short. High voltage on the other hand would arc, spark, or create a fire or other damage. Now, if you were to run those same low voltage signal wires with high voltage wires, and the short happened between the two, you could have those low voltage wires shorting or sparking (especially if the LV wire was not rated for the HV wires voltage or current). If you keep the two seperate, this doesn't ever really become a concern. Signal wires also don't have to be grounded or isolated to the degree of voltage carrying wires, so you could pose an electrocution risk depending on the implementation.

 

[Dgonza9]

Thanks for the advice, guys. Hoping to get this panel up and running soon. I'll be running a separate conduit line for the signal wires.

Cheers!