Direct Answer

After adding bonding per the specification, some LV devices now show unexplained interference — was it wired wrong? The answer: bonding itself does not introduce interference; the problem lies in the practice — making a signal loop that should be single-point grounded into a multi-point ground forms a ground loop, or mixing the LV reference ground with the lightning-protection ground introduces power-frequency/stray circulating current. The diagnosis should check whether an extra ground loop has formed, not remove the bonding.

At a monitoring room, after adding bonding per the specification, some devices showed unexplained interference and false operation. Instead of removing the bonding, the practice was checked first: the signal loop was multi-point grounded, forming a ground loop with a power-frequency stray circulating current interfering with the signals. After changing to single-point grounding and clarifying the grounding diagram, the interference disappeared. The key distinction: the interference comes from the ground loop, not the bonding itself — check whether multi-point grounding formed a loop and whether the reference ground was mixed; do not remove the protection measure.

Why:

  • The nature of bonding: pulling all metal bodies to the same potential does not introduce interference;
  • The ground-loop cause: multi-point grounding of the signal loop forms a ring, with circulating current pouring in;
  • The mixing risk: mixing the LV reference ground with the lightning-protection ground brings in power-frequency/stray circulating current;
  • The rectification: single-point grounding, isolation, and a clarified grounding diagram.

Key insight: "The interference comes from the ground loop, not the bonding — check the multi-point loop and the reference mixing; rectify with single-point grounding and a clarified diagram; do not remove the bonding."

At a park, LV false operations appeared after bonding; the cause was a signal loop grounded at both ends forming a ring with stray circulating interference. After single-point grounding, it recovered. Lesson: the protection measure is right, the practice is wrong — the ground loop is the interference source.

1. Why Bonding Itself Does Not Produce Interference

Step one: understand the principle of bonding first.

The nature of bonding:

  • Pulling all metal/shielding bodies to the same potential;
  • Eliminating the potential difference between devices;
  • One potential → no difference-driven current;
  • It itself does not produce interference.

The difference from earthing:

  • Bonding is "connecting";
  • Earthing is "connecting to the earth";
  • Bonding does not change the discharge path;
  • Do not mix the two.

The judgment points:

  • Interference after bonding;
  • It is not that bonding is "harmful";
  • But that the practice introduced a new circuit;
  • Check the practice, not remove the measure.

Key insight: "Bonding pulls all metal bodies to the same potential and eliminates the difference — it itself does not produce interference; the interference comes from the practice, not the measure."

2. The Cause of the Ground Loop Formed by Multi-Point Grounding

Step two: check whether a loop formed.

How the ground loop forms:

  • The signal loop grounded at both ends;
  • The ground wire + signal wire form a closed ring;
  • Power-frequency/stray current flows in the ring;
  • The interference follows.

Typical scenes:

  • A sensor grounded at both ends;
  • The shielding grounded at both ends;
  • The device and the cabinet grounded separately;
  • Multi-point grounding forms a ring.

How to judge:

  • Draw the signal-loop grounding diagram;
  • Find the closed ring;
  • Measure the circulating current in the ring;
  • A ring exists → the interference source.

Key insight: "A ground loop = a signal loop grounded at both ends forming a closed ring — power-frequency/stray current flows in it; draw the diagram, find the ring, and there is the source."

3. The Risk of Mixing the LV Reference Ground with the Lightning-Protection Ground

Step three: check whether the reference ground is mixed.

The mixing risk:

  • Mixing the LV reference ground (signal ground) with the lightning-protection ground;
  • Lightning/power-frequency current enters the reference ground;
  • The reference potential is raised/polluted;
  • Interference and false operation.

Typical problems:

  • The signal ground directly connected to the structural ground;
  • The shielding connected to the lightning-protection ground;
  • The reference ground mixed with the earthing busbar;
  • Circulating current enters the signal circuit.

How to judge:

  • Check the signal-ground routing;
  • Whether it shares a point with the lightning-protection ground;
  • Measure the reference-ground current;
  • Mixed → isolate and rectify.

Key insight: "Mixing the LV reference ground with the lightning-protection ground lets lightning/power-frequency enter and pollute the reference potential — check the signal-ground routing; mixed, isolate."

4. The Typical Phenomena of the Ground-Loop Interference

Step four: recognize the interference features.

Typical phenomena:

  • Signal fluctuation/drift;
  • Intermittent false operation;
  • Communication bit errors/packet loss;
  • Power-frequency ripple superimposed.

The difference from strikes:

  • Strike interference is instantaneous;
  • Ground-loop interference is persistent;
  • The power-frequency circulating current exists continuously;
  • The features are distinguishable.

The check points:

  • Whether the interference persists;
  • Whether it relates to the load changes;
  • Look at the circulating waveform with an oscilloscope;
  • Phenomenon → loop → rectification.

Key insight: "Ground-loop interference is persistent (signal fluctuation/bit errors/false operation), while strike interference is instantaneous — the persistence distinguishes them; confirm the waveform with an oscilloscope."

5. Rectification: Single-Point Grounding, Isolation, and a Clarified Diagram

Step five: how to change it.

The rectification principles:

  • Single-point grounding of the signal loop;
  • Isolate the reference ground from the lightning-protection ground (or follow the specification);
  • Single-end grounding of the shielding;
  • Clarify the grounding diagram.

The concrete measures:

  • Single-point grounding of the sensors/devices;
  • Single-end grounding of the shielding (at the signal end);
  • Isolate the reference ground from the structural ground;
  • Draw and execute a clear diagram.

Practice verification:

  • Whether the interference disappears after the change;
  • See the earthing state with the FR monitor;
  • The diagram matches the reality;
  • A data loop; the measure retained.

Key insight: "Rectify in three steps: single-point grounding, reference isolation, clarified diagram — verify the interference disappears; keep the protection measure and do not remove the bonding."

6. Product Implementation: Monitoring and Troubleshooting as One

WeiWuLian products manage bonding troubleshooting:

  • FR Earth-Resistance Monitor: online earthing state/resistance;
  • Grounding-diagram management: clear circuit routing;
  • Loop check: multi-point-loop data;
  • Closed-loop verification: interference data comparison after the change.

The design principle in one sentence: "Bonding is right, the practice needs a check — single-point grounding + isolation + a clarified diagram; the FR sees the state online; the interference gone means it is right."

7. Common Misjudgments

  1. "Bonding is harmful, remove it": confusing the measure with the practice. Result: losing protection. Correct: check the ground loop.
  2. "Multi-point grounding is more reliable": ignoring the loop. Result: circulating interference. Correct: single-point grounding of the signal loop.
  3. "The reference ground can go anywhere": ignoring the mixing. Result: potential pollution. Correct: isolate the reference ground.
  4. "Ground the shielding at both ends": ignoring the single-end principle. Result: the shielding forms a ring. Correct: single-end grounding.
  5. "No verification after the change": ignoring the loop. Result: the problem remains. Correct: verify and compare the data.

Scope and Limitations

This article explains the troubleshooting of device interference/false operation after adding bonding (the bonding principle, the ground-loop cause, the reference-mixing risk, the typical phenomena and the rectification direction), applicable to troubleshooting interference caused by improper bonding practice. The exact requirements follow GB 50343-2012 and the manufacturers' data; this article explains only the diagnostic logic and rectification points. All cases are anonymized (a monitoring room, a park) and do not refer to any specific customer.