Should a shielded cable ground both ends?

June 21, 2023

How to ground the shielded cable is a common problem when people do electrical work. Many people ask us: Should a shielding cable ground both ends or one end? This answer is not very definite. Different situations need different analyses. This article will show some knowledge you should know about PVC shielded wire.

This article mainly includes three parts:

  • What is a shielded cable
  • The shielded cable ground method
  • Should a shielded cable ground both ends

First of all, we should know what is a shield wire.

What is a shielded cable

A shielded electrical wire structure includes not only a copper conductor, PVC insulation, and PVC outer sheath, different from other electric power cables, but also a shielding layer. This shielding layer makes it has an important shielding function. Shielded copper wire also includes double-shielded cable and single-shielded wire. Double shielding wire has two layers of shielding, single shielding wire has only one layer of shielding. The shielding layer can well protect the signal transmission from interference and safety. Below is a picture of shielded copper wire.

shielded cable

Next, we will introduce the shielding cable wire ground method.

The shielded cable ground method

Usually, there are three methods when grounding: single ground, double ends ground, and shield suspension.

Single grounding method

Imagine the signal current i1 enters into the shielding wire from the conductor, after flowing through the load resistor RL, it will return to the signal source through the shielding layer. Since i1 and i2 are equal in size and opposite in direction, the magnetic interference they generate cancels each other out. This is a good measure to suppress magnetic field interference. At the same time, it is also a good measure to resist magnetic field coupling interference.

Double ends grounding method

Since the current flowing on the shielding layer is the superposition of i2 and the ground ring current iG, it cannot completely cancel the magnetic field interference generated by the signal current. Therefore, its ability to suppress magnetic field coupling interference is also worse than that of single-ended grounding. Both the single-end grounding mode and the two-end grounding mode have the effect of shielding electric field coupling interference.

Shield suspension

Only can shield electric field coupling interference, but not the ability to suppress magnetic field coupling interference.

Now, we will discuss should a shielded instrument wire ground both ends.

Should a shielded cable ground both ends

Whether a shield wire should ground one end or both ends, is not an absolute question. Under some circumstances, one end grounding is OK, but under other circumstances, both end grounding is OK. Here are some introductions about it.

  • The shielding layer of the analog signal circuit control cable of the computer monitoring system shall not form a two-point or multi-point grounding and a centralizing one-point grounding should be using.
  • When the interference of electromagnetic induction is large, it is advisable to use two-point grounding; If the interference of electrostatic induction is large, it can be grounding at one point. For double shielding or composite overall shielding, one point should be using for the inner and outer shielding, and two points should be grounding.
  • The choice of two-point grounding should also consider that the shielding layer will not be melting under the action of the transient current. When a shielding cable is using, the shielding layer should equipotentially connects at least at both ends. When the system requires only one end to be equipotentially connected, two layers of shielding should be using, and the outer shielding should be treated according to the aforementioned requirements.
  • The transmitting end is grounding, and the receiving end is grounding through a capacitor.

At this point, the outer shield induces a current due to the potential difference, thereby generating a magnetic flux that reduces the strength of the source magnetic field, thereby essentially canceling the voltage induced without the outer shield. If it is to prevent electrostatic interference, it must be grounding at a single point, whether it is a layer or a second layer of shielding. Because the electrostatic discharge speed of single-point grounding is the fastest. However, there are two exceptions:

  • There is strong external current interference, and single-point grounding cannot satisfy the fastest discharge of static electricity. If the cross-sectional area of the grounding wire is large to ensure the fastest discharge of static electricity, it must also be grounding at a single point. For example, the cable tray in the enterprise is the outer shielding layer, which must be grounding at multiple points, the first line of defense, and reduce the strength of the interference source.
  • Safety requirements such as external electric shock and lightning protection. In this case, we require two layers of protection. The outer layer is not using to eliminate interference but for safety reasons. To ensure the safety of people and equipment, multiple points must be grounding. The inner layer is to prevent interference, so it must be grounding at a single point.

Now, you must understand the usage of shielded cable, if you still don’t know how to ground the shielding wire, you can enter Henan Shenbei Industrial Co. Ltd., which sells all kinds of control cable, house wiring cable, communication cable, and instrument cable. 24-hour customer services are also waiting for solving all of your questions.

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