Seals for electromagnetic shielding

Sources and receptors of electromagnetic disturbance 

Remember that all electrical and electronic equipment are sources of electromagnetic disturbance, which means they have the potential for causing problems in other devices. They can also be affected by electrical interference, which means they are receptors as well.

Common sources

• Radio, TV and radar equipment
• Electric power lines
• Electronic circuits
• Light dimmers
• Arc welders
• Electric motors
• Electric storms and large solar flames
• Electromagnetic pulse weapons

Receptors (potential victims)

• Radio and TV receivers
• Appliances
• Computers
• Electronics 

Eliminate the coupling paths

Sources and receptors are no problem as long as they are not connected. You can achieve protection against electromagnetic threats through elimination of the coupling path, which is the connection that transfers the disturbance from the source to the receptor/victim. 

The Roxtec ES system provides an effective protection when used in shielded environments. The system both diverts conducted disturbances and shields against radiated disturbances.

Conducted coupling path – the electromagnetic disturbance travels via cables and pipes. The coupling path could be either inductive magnetic coupling or capacitive electrical coupling.

Radiated coupling path – the electromagnetic disturbance travels via air as a wave. Its energy is absorbed and generates a current flow in the receiving cable/pipe or directly in the electronics.

The Roxtec ES system

The purpose of Roxtec ES transits is to improve the electromagnetic compatibility between different electric and electronic devices through electromagnetic shielding. The system is a modular-based cable and pipe transit for electromagnetic shielding applications as well as a mechanical penetration seal. It has a dual function – preventing electromagnetic fields and providing environmental protection against risks such as fire, gas, water, dust, dirt and rodents.

System components

The system consists of an electrically conductive steel frame, Roxtec ES modules, stayplates and a compression unit plus lubricant for use during installation. The frames come in different shapes and sizes. You can incorporate them into the construction, either during the building process or after, to make openings for cables and pipes passing through walls and partitions. 

A continuous electrical connection to the shielded structure is vital. You insert Roxtec ES sealing modules into the frame to seal around the cables and pipes. Then you enter the compression unit, the Roxtec Wedge ES, and tighten it to add compression and complete the seal.

Tested for electromagnetic shielding

Once complete, the Roxtec ES seal protects the penetration and any attached equipment from induced electromagnetic disturbances. The seals have undergone numerous types of tests performed by different authorities, for example shielded attenuation tests according to standard IEEE 299 and transfer impedance tests according to standard VG 95373-15. 

Roxtec ES (Electromagnetic Shielding) modules

Roxtec ES sealing modules, marked with white stripes, have two components, each taking care of its own particular type of electromagnetic disturbance. The modules protect against unwanted electromagnetic energy carried by currents in the cable shield and divert them to ground. They further protect against unwanted radiated electromagnetic energy, thanks to an electrically conductive rubber material inside the modules.

The Roxtec ES module consists of two identical halves, which form a single unit when installed. Cylindrical, concentric layers of rubber make up the center of it and are removable to allow a tight fit to the cable. The rubber layers enable you to adapt it to both the diameter of the cable jacket for environmental protection and to the cable shield for electromagnetic protection.

• Conductive rubber – through the center of the module, perpendicular to the cylindrical rubber layers, runs a layer of conductive rubber. It acts as a barrier for radiated electromagnetic disturbances.
• Conductive foil – a conductive, low impedance foil is wrapped around the module and extended to cover 360 degrees of the cable shield. The foil is in continuous contact with the conductive rubber and the cable shield and connects all the modules in the metal frame. The foil diverts disturbances absorbed by the conductive rubber barrier and the cable shield or pipe through the frame to the shielded structure. 

Ensure 360-degree continuous connection

Roxtec ES transits are vital components when you want to maintain a high level of shielding performance for electronic and electrical equipment housed in a shielded volume. It may be in the shape of an equipment enclosure, room, building structure, platform or vessel.

The Roxtec ES cable and pipe seal acts as an integrated part of the shield surrounding the equipment. The shield is a barrier for the electromagnetic energy, whether it is in the form of radiated or conducted electromagnetic fields.

In the Roxtec ES system, the conducted disturbances are diverted to the shielded structure via conductive foil. They are thereby removed from the coupling path and shielded cable or pipe. The radiated disturbances are reflected and absorbed by the conductive rubber layer. The layer covers the cross-section of the modules, and it is perpendicular to the individual cable inlets.

How to measure shielding effectiveness

A common method is according to the IEEE 299 standard with a self-generated RF signal. The test setup is calibrated by placing a transmitting and a receiving antenna with no barrier in between, and by measuring the received signal level. Then the receiving antenna is placed at the same distance, but inside a shielded enclosure. The signal level is measured again, and the difference in received signal level is the shielding effectiveness, normally expressed in dB.

Illustration of measuring test system – transmitting and receiving antenna placed on separate sides of the electromagnetic barrier.

Typical electrical characteristics, Roxtec RM ES systems.

Roxtec seals are tested according to standards for shielded enclosures, such as IEEE 299. They are fitted into the wall structure before measuring the shielding effectiveness of the complete enclosure.

The Roxtec ES sealing system is available in versions approved for use in hazardous locations. Explore Roxtec ES Ex transits.