As the demand for electricity continues to rise, the installation of larger and more powerful transformers, along with their associated cabling, has become more prevalent. As a result of this, there has been an increase in the levels of power frequency electromagnetic interference (EMI) emitted from these equipment rooms and devices.

All high current sources in a building, such as transformers, bus bars, switchgear and power distribution cables, produce magnetic fields. These fields can pass through standard building construction materials and induce currents in the human body or electronic devices.

If intense enough, the radiated magnetic field can affect electronic equipment and the health and wellbeing of the building's occupants. The guideline reference limits applicable in the UK are those published by the International Commission on Non-Ionising Radiation Protection (ICNIRP).

For public exposure, the ICNIRP states that for power frequency (50Hz), magnetic field limits are to be no greater than 100μT. These public exposure reference limits are outlined as UK government policy but are similar across Europe. In addition to this, epidemiological studies have indicated that prolonged exposure to power-frequency magnetic fields above 0.4μT is associated with a small absolute raised risk of leukaemia in children. Although this level is not currently law, it is prudent to consider this finding when designing or specifying a residential building electrical systems.

In Europe and the UK, electronic devices are tested to operate in magnetic fields set out in BS EN 61000-4-8.
Depending upon the environment, an equipment class and test level is given.

Class 1 – 1A/m (1.26μT)
Class 2 – 3A/m (3.78μT)
Class 3 – 10A/m (12.6μT)

This is the maximum level at which the electronic device has been tested and is designed to operate. Higher field levels could affect the electronic equipment and prevent it from operating correctly.

To protect people or electronic devices from the effects of high levels of magnetic fields, shielding is required.

Mag-stop shielding provides an effective solution to reduce power frequency (50/60Hz) magnetic fields to levels less than 0.4μT.

Each project is individually designed and areas of concern are identified. Shielding thickness and required attenuation levels are calculated and all penetrations of the shield are designed and manufactured. Full support through the consultation phases and design stages can be provided by Global EMC.

Mag-stop is available in fully seam welded sheet format to line the surface of the room or as a “pan” type modular system that requires no hot works on-site. Mag-stop is also complemented by Armadillo shielded containment for electrical cable tray or trunking shielding throughout the building.