EMF Shielding

Magnetic shielding is a process that limits the coupling of a magnetic field between two locations.

Unlike electricity, magnetic fields cannot be blocked or insulated, which makes magnetic shielding necessary.

This is explained in one of Maxwell’s Equations, del dot B = 0, which means that there are no magnetic monopoles. Therefore, magnetic field lines must terminate on the opposite pole.

There is no way to block these field lines; nature will find a path to return the magnetic field lines back to an opposite pole. This means that even if a nonmagnetic object — for example, glass — is placed between the poles of a horseshoe magnet, the magnetic field will not change.

Instead of attempting to stop these magnetic field lines, magnetic shielding re-routes them around an object. This is done by surrounding the device to be shielded with a magnetic material. Magnetic permeability describes the ability of a material to be magnetized. If the material used has a greater permeability than the object inside, the magnetic field will tend to flow along this material, avoiding the objects inside. Thus, the magnetic field lines are allowed to terminate on opposite poles, but are merely redirected.

Requirement for EMF Shielding

EMF shielding is required where there are occupied areas (apartments, offices or retail spaces) located next to or above substations, switch rooms or high current power cabling, to reduce occupants exposure to 50 Hz EMF fields associated with the high current carrying cables and transformers.

Areas outside external building walls, parking garages and walkways or thoroughfares are not normally considered to be occupied areas as they are only used for transitory purposes (i.e. no long term occupation)

As a general rule 4 layers of “M36 shield” EMF shielding material is applied to these installations. The sheets should be applied to all surfaces between the substations and/or switch rooms and occupied areas and should extend a further 1 m around the adjacent wall.

EMF Shielding material

“M36 Shield” is ideal for EMF shielding of 50 Hz power frequency magnetic fields from substations, switchboards and associated electrical cabling.

When magnetic fields encounter “M36 Shield”, the magnetic forces are both absorbed by and redirected away from the area of concern.

“M36 Shield” is supplied in individual sheets measuring 1 m x 2.4 m x 0.5 mm. Typically 4 or more layers are required with the butt joints of each layer staggered away from the butt joint of the layer below.