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How is the shielded wire grounded?

Date: 2019-11-12   Source: Weiqi

Shield line grounding method: short-circuit the shield line and the circuit ground potential, and the other end is suspended.


One end of the shielded wire is grounded and the other end is suspended. When the signal line transmission distance is relatively long, the grounding resistance of the two ends is different or the PEN line has a current, which may cause the two grounding points to have different potentials. If the two ends are grounded, the shielding layer has a current, but the signal is Interference is formed, so in this case, one grounding is generally used, and the other end is suspended to avoid such interference. The grounding shielding at both ends is better, but the signal distortion will increase.


"GB 50217-1994 Power Engineering Cable Design Specification" - 3.6.8 The grounding method of the control cable metal shield shall comply with the following provisions:

(1) The analog signal loop control cable shielding layer of the computer monitoring system shall not constitute two or more points of grounding, and it is recommended to use a centralized one-point grounding.

(2) In addition to the (1) item and other control cable shields that require a little grounding, when the electromagnetic induction interference is large, two points of grounding should be used; the electrostatic induction interference is large, and one point can be grounded. For double shield or composite total shield, it is better to use one point for the inner and outer shields and two points for grounding.

(3) The choice of two-point grounding should also consider that the shielding layer will not be melted under the action of transient current. "GB50057-2000 Building Lightning Protection Design Code" - Article 6.3.1 stipulates: ... When shielded cable is used, its shielding layer should be equipotentially connected at least at both ends. When the system requires only equipotential bonding at one end Two layers of shielding shall be used, and the outer shielding shall be treated as described above.