Certain environments are notoriously harsh on electrical equipment, creating unique challenges for product engineers, particularly when it comes to selecting cable and connector assemblies. Design teams are quick to consider elements such as resistance to extreme temperatures, dust and water ingress, chemicals, and mechanical stress, but one menacing factor often gets overlooked — electromagnetic interference (EMI).
Any device that contains electronic circuitry is susceptible to EMI, which is a phenomenon that occurs when conducted and radiated electrical signals from one device or system cross paths with another. For example, early cellphone users occasionally picked up a stranger’s signal while on a call, resulting in what we refer to as “crosstalk”. In such cases, one or both parties could randomly hear bits of the other’s conversation. Today, younger generations probably haven’t experienced crosstalk because modern circuit boards utilize shielded wires to deflect EMI interference and prevent devices from emitting EMI.
Mission-Critical Applications
If EMI occurs in industrial, medical, security monitoring, public safety, marine, transportation, and other important applications, the consequences can be far worse than a little crosstalk, ranging from a dropped data, GPS, or power signal to total cable failure and life-threatening repercussions. The greatest offenders of EMI are equipment and processes that involve:
- Drives
- Solenoids
- Motors
- Generators
- Transformers
- Electrolytic processes
- Power lines
- Telecommunications
How Do Shielded Cables Work?
Shielding uses a metallic material (typically copper or aluminum) to encapsulate wires and deflect EMI. While variations do exist, design teams generally choose between three basic types of shielding:
- Foil shielding
Uses a thin layer of aluminum, which covers the entire conductor at 100%. Foil shielding typically utilizes a drain wire in order to terminate and ground the shield and is relatively inexpensive. However, this type of shielding can be more difficult to work with due to the thinness of the foil material, which is prone to tearing (especially when affixing a connector). - Braided Shielding
Uses thin strands of copper or tinned wire to form a tubular lattice “wrap” around conductors. Due to its woven design, braided shielding only offers about 70% to 95% coverage. However, because copper has higher conductivity compared to aluminum, and the woven design adds bulk for conducting EMI-related noise, braided shielding is considered the more effective option. - Hybrid Shielding
For extremely noisy environments, both foil and braided shielding can be layered over one another to cancel out the vulnerabilities in each, thus providing optimal coverage. Both shielding options can also be used on different parts of a cable. For example, in multiconductor cables, individual pairs can be shielded with foil to prevent crosstalk while the cable itself is protected by a layer of braided shielding or multiple layers of foil and braided shielding.
Selecting The Right Shielded Cable and Connector
Here are some guidelines to help you select the right shielded cable and connector:
- In fairly noisy environments, foil alone can provide adequate protection.
- In noisy environments, stick to braided shielding.
- If the environment is extremely noisy, use a hybrid shielding solution.
- If searching for a flex cable, steer clear of both foil and braided designs and opt for a spiral shielding instead.
Lastly, because eliminating noise will depend on having a low resistance path to ground, be sure to ground shielded cables at one end using an earth ground whenever possible. For more information on the best way to shield cables and connectors, download our whitepaper.
