AC conductors perpendicular to DC conductors

[ByDesign]

All,

Good engineering practices for routing AC and DC conductors in seperate raceways and where they cross they should cross at 90 degrees to each other.

I've been doing this for years and now I have to provide either code or good engineering practices guide that "Proves" that AC and DC conductors crossing at 90 degrees is OK.

Any ideas where I can find the code/text to clarify this?

Thnks for your time!

Scott

Have a great day!

Scott

 

[itsmoked]

This is only the case when you have small "signals" running next to power. Signals like pressure sensors or thermocouples, or very high power. It certainly isn't a NEC/fire/electrocution subject!

I don't think the NEC or any other regulatory body will care about it. I don't think you will find it.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[IRstuff]

The counterargument is to simply point out that anything other that a 90º crossing will introduce more inductive and capacitive coupling.

TTFN

 

[Skogsgurra]

Are you talking heavy currents in AC and DC? Or weak signals in DC? Or weak signals in both?

In the first case, there are no reasons to fear any bad effects. It is just a lot of extra cost to arrange those 90 degree crossings - if they don't come naturally.

In the second case, there is a very real risk of inducing interfering signals in the DC signal cable. No proof should be needed. It is obvious to anyone that knows about magnetics and electricity. But problems very seldom manifest themselves.

In the third case, there is not much magnetic coupling. The problem is more the capacitive coupling. Screened cables solve that problem.

I have had this discussion so many times. And many people have a strong conviction that it is a catastrophy if the crossing isn't under 90 degrees. I often bring those guys with me for a tour in the plant. There are sooo many non-90 crossings (or rather parallel runs) to be seen. And no problems with the plant.

All these "dos and don'ts" stem from a time when equipment were built to handle lab environment - but seldom real-world interference. Many manufacturers put warnings up front in their manuals to the effect that the installation was wrong - not the equipment. Often in bold, black letters.

Since this was what most people remembered (saw) from the manuals, it stuck in their minds. The situation is somewhat different now. But a good scapegoat shouldn't be killed just like that. So the 90 degrees are still live and kicking.

Gunnar Englund

http://www.gke.org