An introduction to Shielding

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Written by Scott Mulholland, Product Manager- Industrial Components

To be clear, this blog is not about the shielding you now have to do when you return from a foreign country due to the COVID-19 threat. We are going to look into the other type of shielding.

So, what is shielding?

When electrical/electronic devices are powered up, they create electromagnetic fields around them. These fields can have an influence on other machinery/devices/equipment surrounding them. This potentially can:

  • Affect equipment performance
  • Generate ‘ghost’ switching
  • Stop the equipment performing all together
  • Affect equipment outside of your cabinet

There are different types of interference:

  • Electromagnetic interference (EMI)
  • Radio frequency interference (RFI)

Because of this interference, we need some assurance that our equipment/machine will function as expected. We need to be sure that our equipment meets or achieves EMC.

‘Electromagnetic compatibility (EMC) is the ability of electrical equipment or systems to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment’

Source: IEC 61000-2-1 (Definition EMC)

So, in short, we want to be sure that our equipment is immune from fields created by other equipment/machines, but, equally as important, we need to be sure that our equipment is not emitting troublesome fields.

The IEC is very clear about the levels that need to be attained to classify equipment as EMC. It also makes the distinction between residential/commercial and industrial.

A person sitting in a dark room

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So how do we make our equipment EMC? Well, we utilise the Faraday principle. Faraday being Michael Faraday (1791-1867). That’s this handsome chap on the right.

Faraday is best known for his studies and experiments on charge, magnetism and their interaction. He observed that charge on a conductor only resided on the outer surface. He also noted that nothing inside that conductor was affected by any change in electrical charge on the outside.

Field theory was based on Faraday’s work (which built on the work of Benjamin Franklyn). His work led to the understanding that electrostatic repulsion of like charges causes a redistribution of charge to the outside of a conductor resulting in a net electrostatic field within the conductor of zero. (“Within the conductor” means any space enclosed by a continuously conducting layer. ) An example of this can be seen in this video.

When we shield our equipment, machine or panel we typically mechanically ground the equipment directly (with shield clamps) and/or make use of the shield foil/braid in a shielded cable:

Image result for shielding foil in cable

We do this with a view to negating the effects of coupling. Here we can see how our equipment can become coupled (or adversely influenced by) other nearby equipment.

In everyday terms, this is how the different types of coupling affect our equipment.

Apologies if I’ve painted a bleak picture regarding how vulnerable your equipment may be, but I do believe it is important to be aware of the potential pitfalls. Do not fear though, help is at hand. Phoenix Contact has a comprehensive portfolio of products to help you make your equipment EMC. On our UK website, all of this portfolio is grouped here.

And we also have most of our SAC sensor actuator cable offer with shielded options. Further to this in our SAC range, we have introduced our AST (advanced shielding technology) cable range. The only sensor cabling on the market to offer what can truly be demonstrated as full 360 degree shielding around the cable cores.

We have also turned our innovative eye towards bringing the humble cable shielding clamp up to date. Our new SCC shield clamps are spring actuated rather than screw. This makes them very quick to install, gives them a uniform pressure for retaining/securing the cable and makes them impervious to the effects of vibration.

We have focused brochures to help you select the right shielding solutions for your application.

Download SCC-Shielding Clamps brochure
Download Sheilding brochure

As the number of pieces of ‘intelligent’ equipment rise, as the “internet of things” becomes more and more prevalent in our lives, shielding will become increasingly important to protect the integrity of your equipment. Phoenix Contact can support you in protecting your applications.

For more information contact Scott on 07908 583375 or email



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