Cable management systems for Electromagnetic emission control

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Cable trays, conduit, ladders – all examples of cable management systems (CMSs) designed to hold cables in place. Only they can do much more than that. 

For the last few years, some of us in the electrics industry have been seeking to raise awareness of the crucial role CMSs play in shielding the electromagnetic emissions from cables.
Far too few users across industry think of them in those terms. Sure, they know that CMSs can mitigate electromagnetic radiation. But it’s not enough merely to mount cables on, say, a tray and presume that will do the job. Different CMSs afford different degrees of protection.

It is critical to design the right CMS – the one that meets your needs – into your installation from the outset.

What are consequences of the wrong CMS?

The consequences can be dire. Safety compromised, production affected, crippling costs. Why? Because by the time you realise it, it’s too late to change your CMS. It’s difficult and very costly to remove and replace cable trays. Sometimes it’s plain impossible. You may just have to live with it.

So, stop and think what your needs are. Then factor them into your choice of CMS. And start with right metal.
What kind of metal should you use?

That depends on the nature of the field and the frequency spectrum. A rule of thumb is to use iron or steel if the field is mainly magnetic. For high frequency electric fields, go for conductive metals like copper or aluminium.
But what if you have 50 or 60Hz cables carrying high currents. They will radiate magnetic fields in the main. But if you disregard the strength of the magnetic field, it will be determined by current, so your CMS should made of high-permeability metal. It will absorb the magnetic field efficiently – if it’s thick enough. I mention these parameters just to stress that the only effective CMS is the one that meets your needs.

What kind of CMS arrangement affords the best protection?

Let’s take trays. They fall into three broad categories according to their apertures, as the illustration shows.

Meshed basket trays have attenuation capacities of between 12 and 24dBs depending on whether or not they are covered. Perforated ones afford better protection – up to 30 dB if covered. The less apertures there are, the more comprehensive the protection. But one that is fully enclosed – Faraday cage-like – doesn’t allow heat to dissipate, although it boasts an attenuation capacity of 50dB. Something to bear in mind, if that’s your choice.

How can I determine which tray best meets my needs?

I’ve come across instances of meshed trays with wide apertures being used in data centres where the magnetic fields are tremendous. Not an example to emulate.
If you know your installation and it complies with electromagnetic emission standards. And if your power cables and those carrying sensitive signals – from sensors, for example – are screened and well separated you can use a mesh basket tray.
If you’re not sure about your electromagnetic environment, but know that you’ve got to keep the emissions down, then a covered perforated tray might well be the right choice. Especially if different signal-carrying cables aren’t segregated.
A plain tray with no vents is the wisest solution if the electromagnetic environment is harsh and shielding has to be effective.

What of CMSs in the future?

There’ll be more and more need for them as installations grow more complex and sensitive and electromagnetic effects increase. Let’s open our minds to the properties and possibilities of CMS. Then carefully choose the right one. And choose it early.
Have you chosen the wrong CMS? Want to know more?