Cable Tray/Conduit Spacing 1

[lilbobo]

I have a standard from a particlar company on cable tray and conduit spacing based on the particular types of signals, voltage levels, etc. carried by the cables in the said cable trays/conduits. The lineal distance of the said cables also plays a factor in the recommended spacing of cable trays and conduits. For example, a cable tray carrying RTD and low level DC signals running in parallel beside a cable tray carrying 120VAC must be spaced at least 6 inches for every 100 lineal feet that the cable trays are running in parallel. The goal of this standard is to seperate high noise producing cables from sensitive cables.

What I am trying to find is where this standard came from? Or if there are similar, perhaps updated, standards written on the subject? I've looked through the NEC and CEC thoroughly but have limited access to ISA and IEEE standards.

 

[dpc]

I don't think you're going to find anything related to this in any standards. These are engineering judgements based on experience, historical practice, scar tissue, and other intangibles.

There may be corporate standards but I don't believe there are any consensus standards or codes that will address this in detail.

A lot of people would run everything in the same conduit, if not the same cable and often get away it. I'd be more concerned about the type of cable I was using than the conduit spacing - at least until I got up to the 480V level.

You'll definitely want to make sure your standard includes keeping VFD output wiring (to the motor) in its own steel conduit.

 

[SpecialSystems]

Standards will be in the NEC for wiring in Cable trays. There maay also be something under EIA/TIA standards regarding the cable tray requirements in regard to telecomm wiring. But no standard that I know of for conduit to conduit other than what the above gentleman stated. Conduit to conduit will depend on the power being run in the conduit versus the type signal on the cables in the other conduit. As a General rule when running High level power or signal adjacent to Low level power or Signal, it is a good idea to try to seperate them.That may be from 2 inches to 1 foot depending on the signal levels (example: you may have a high voltage or high energy signal running next to a video cable. Video is one volt peak to peak, high level could bleed over and cause issues).
As far as spacing into the tray, unlees its a manufacturers requirement to meet some UL standard, I do not know of anything..

 

[rbalex]

There are references in the NEC that specify certain separations in Chapter 7, Articles 725, 760, 770 and 780 and Chapter 8.

Theoretically these are safety rather than performance related.

At one time, "noise susceptibility" was the topic for IEEE-518, but I am not sure if the Standard is still active. ISA (

http://www.isa.org)

now has recently assumed jurisdiction on the issue but I'm not sure which Document covers it.

 

[itsmoked]

I once went to do a complete an installation on an ETO sterilizer chamber system. The whole thing was dripping with intrinsic safety stuff. I had pre-built all the enclosures and controls and sent them ahead to be plumbed and wired before I appeared and commissioned the beast.

When I got there I found that they had followed all my instructions about wire type separations within my enclosures as I make them with the hazardous (barriered area) wires allowed only in high contrast brightly colored reflector tape areas. Unfortunately they ran these hazardous wire out into a wiring duct that was 50% filled with 480V stuff...

The general logic is to keep the hazardous signals at least far enough away from non-protected wires that a long drill bit run in any direction cannot connect the two types. This means definitely not in the same wire run space. Noise concerns like VFD / small signal may require additional spacing.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com