Shielding and Why it’s Important. [Cable 101]

Whether designing a disposable medical device, mass-producing a consumer charging cable or developing a wire harness for a piece of capital equipment, careful detail must be paid to connect the different components. This coming-together is most typically accomplished using some version of wire. Unbeknownst to the majority of the general public, this much design and engineering go into each type of wire. We discussed the conductor and insulation for both carrying the charge and not losing the electrical charge, but now the question is—how do we keep outside influences from interfering with our wire’s signal?

Before we discuss what the “shield” is, let’s review the very basic anatomy of a wire. Within a “simple” wire you have, moving from inside to outside;

1. Conductor
2. Insulation
3. Shield
4. Jacket

What is “shielding”?

A shield is most commonly constructed of either foil or a woven mesh braid.

Foil Shielding is a layer of aluminum that is attached to the carrier. The foil layer method is the only shielding option that provides total coverage of the conductors—particularly important with data cables. Foil shielding is thin which can increase the complexity of the production of the wire.

Braid Shielding, also referred to Mesh Shielding is produced using thin wires. This method of shielding provides low resistance path to ground, it is a less complex medium in production but does not provide the total coverage that the foil shielding provides, due to the small gaps resulting from the braiding manufacturing process. Expected coverage for a braided shield is 70%-95%—70% coverage is sufficient for most applications.

When to use Foil over Braid or vice versa?

• Positives of Foil:
  • Thinner, allowing for a smaller diameter wire
  • Less expensive
  • Complete coverage—therefore better protection from electrostatic interference
• Positives of Braid:
  • A more effective shield than foil
  • Additional strength, harder to penetrate and flexible
• Negatives of Foil:
  • Not as effective shield as braid
  • More easily penetrated
• Negatives of Braid:
  • Limited coverage
  • More expensive than foil
  • Adds size to the diameter of the wire

Do you ever use both Foil and Braid together? Yes

In “noisy” environments, it is common to use a combination shield—foil layer followed by a braided layer. In multi-conductor applications, it is not uncommon to shield the individual pairs with foil and then shield to complete wire with a braided shield. This provides “cross-talk” protection.

As we’re beginning to see, so much goes into just the cabling of a connector and we haven’t even started in on the connection portion of the interconnect.

Next blog post in the series: Jacket

Previous blog post in the series: Insulation