Diagnosing “Ghost Faults”

Diagnosing "Ghost Faults"

Key Takeaways

“Ghost faults” are intermittent electrical disturbances that defy easy reproduction or continuous observation.
A systematic diagnostic approach—starting with inspection and proceeding through power-quality and grounding checks—greatly improves chances of root-cause resolution.
Common underlying causes include intermittent arcing, moisture-induced ground leakage, and switching transients.
Corrective actions often involve tightening or reworking connections, improving insulation integrity, hardening systems to modern equipment requirements, or repairing grounding systems.

Introduction

Ghost faults—also sometimes called phantom or elusive faults—are intermittent electrical anomalies that cause unexpected and unwanted behavior in equipment (e.g. nuisance trips, resets, flickers). Because they tend to appear and vanish unpredictably, they resist simple measurement and can lead to wasted time chasing phantom issues, or prematurely replacing functional components.

Here outlines a structured path to diagnosing ghost faults, with emphasis on observation, measurement, and elimination of likely suspects.

Recognizing the Telltale Signs of Ghost Faults

Ghost faults typically present in the following ways:

Nuisance tripping or resets: Circuit breakers, residual-current devices (RCDs), or protective relays may trip for no apparent cause.
Equipment reboots / lockups: Controllers or PLCs may reset or lock up.
Flicker, dimming, or voltage dips: Lights may dim briefly or flicker, particularly when other loads switch on or off.
Intermittent error codes: Equipment may report errors that do not persist or are costly to diagnose.

“Nothing found” during inspections: Because the fault is intermittent, casual inspection often results in “everything looks fine.”

Because of the nature of transient overvoltage, capturing this particularly challenging anomaly often requires expensive logging tools, event records, and correlating occurrences with external events (e.g. motor starts, switching operations, rainfall) to reveal patterns. This is a resource intensive and often costly endeavor.

Visual & Physical Inspection

A careful visual and hands-on inspection is the foundation of diagnosing phantom faults. Focus your attention as follows:

Panels, junction boxes, and terminal blocks

Look for signs of overheating: discoloration, charring, melted insulation, or scorch marks.
Check for loose or corroded terminals, damaged connections, or vibration-loosened screws.
Inspect conductor insulation for cracks, cuts, abrasions, or embrittlement.
Examine cable bending points for mechanical stress.

Moisture ingress or contamination

Look for signs of moisture, condensation, rust, or salt deposits, especially in outdoor or unsealed enclosures.
Check gasket seals, conduit seals, and junction box covers for integrity.

Vibration and mechanical stress

In high-vibration environments, connections may loosen over time; consider retorquing per spec.
Ensure cables are properly strain-relieved, clamped, and secured to prevent movement.

Component condition

Replace any terminals, lugs, or blocks exhibiting wear or damage.
Use thermal imaging (infrared camera) to scan under load; hot spots can betray a weak connection that might arc sporadically.

Torque verification

Using a calibrated torque wrench or screwdriver, verify that connection bolts and screws are torqued to the manufacturer’s specification.
If any terminals are loose or suspect, retorque and then monitor.

After tightening or repairing, do not assume the problem is solved. Continue monitoring under operational conditions, as some faults may only occur under certain loads or transient voltage-inducing conditions.

Grounding & Bonding Inspection

A robust grounding and bonding system is central to preventing ghost faults. Poor or degraded grounding can allow stray currents or floating potentials to intrude unpredictably. Every electrical system needs a stable reference point — usually ground — so that voltages stay within safe, predictable limits. When grounding or bonding is poor:

Stray currents can find unintended paths (through conduit, control wiring, or equipment frames), especially when there are different potential created by inadequate bonding.
Floating potentials develop — parts of the system that should be at the same voltage drift apart electrically.

This creates unpredictable voltage differences between metal parts or circuits that should be at the same potential. That instability is exactly what makes ghost faults so difficult to diagnose.

Inspect grounding electrode system

Check ground rods, plates, or mesh for corrosion, damage, or disconnection.
Confirm integrity of grounding conductors; ensure terminations are tidily made and torqued.
In corrosion-prone environments (soil moisture, chemical exposure), inspect periodically and consider sacrificial enhancements (e.g. copper sulfate, ground rings).

Check bonding of metallic parts

All metal enclosures, raceways, cable shields, and equipment frames should be bonded to the same common ground potential.
Verify that bonding jumpers or straps are intact, low resistance, and properly sized.
Avoid relying on conduit or pipe as the only bonding path in critical circuits unless confirmed adequate.
Verify that neutral and ground conductors are not being used as parallel conductors.

Measure ground system resistance and impedance

Use a ground tester or fall-of-potential method to measure electrode resistance (e.g. target a minimum of ≤ 25 Ω or less, depending on local code/standard).
Use loop or selective ground impedance testers to assess performance under AC fault or transient conditions.
If resistance or impedance is excessive, improve grounding by adding rods, enhancing soil contact, or repairing conductors.

Check for ground loops or floating potentials

In complex systems, multiple grounding points can create circulating currents.
Confirm that signal or control circuits (e.g. instrument grounds) are isolated or referenced correctly.
Use isolation transformers or common-mode chokes if ground loop interference is suspected.

Moisture and insulation breakdown

Even if the main grounding is sound, moisture on insulation surfaces can permit leakage paths to ground that vary with humidity, temperature, or contaminants—causing intermittent ground faults.

Review Power Quality

Ghost faults are often triggered by transient overvoltage, an intrinsic anomoly in electrical systems. As these transient overvoltage events occur in microseconds—far shorter than the sampling rate of standard power quality monitors (PQMs)—they can pass unnoticed even during active monitoring.

To capture meaningful data, use a PQM designed for high-speed sampling (in the mega-samples-per-second range) and equipped with proper bandwidth and triggering capabilities. This ensures the device records the full transient waveform, not just an incomplete spike as this data may be misleading.

Place monitors as close as possible to the affected equipment and run them during normal operations to identify correlations between transient overvoltage activity and observed ghost faults. Look for links to switching events, such as motor starts, HVAC cycles, or lighting controls.

Because transient overvoltage is inherent to every electrical system, use of surge protective devices (SPDs) in conjunction with filters and isolation methods to protect sensitive loads is recommended reguardless if a power quality study is performed.

For guidance on PQM selection, review "Power Quality Monitoring Devices: Recording Transient Voltage"

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Common Causes of Ghost Faults

Below is a table summarizing the most frequent root causes of ghost faults, along with their symptom signatures and diagnostic tips.

Because ghost faults are by definition intermittent, the diagnostic process often involves elimination—correcting one suspect at a time, monitoring behavior, and checking whether the anomaly disappears.

Conclusion

Ghost faults challenge even seasoned technicians because their intermittent nature effectively “hides” them from conventional measurements. However, a structured approach—starting with careful inspection and moving through grounding evaluation and power analysis—gives the best chance of unmasking them.

Resources

“Common Pump-Off Controller Failure Modes and Their Fixes.” Maxivolt, Maxivolt, https://maxivolt.com/home/common-pump-off-controller-failure-modes-and-their-fixes/
“Power Quality Monitoring Devices: Recording Transient Voltage.” Maxivolt, Maxivolt, https://maxivolt.com/home/power-quality-monitoring-devices-recording-transient-voltage/
“Grounding and Bonding for Electrical Safety and Reliability.” Maxivolt, Maxivolt, https://maxivolt.com/home/grounding-and-bonding/
Institute of Electrical and Electronics Engineers (IEEE). IEEE Recommended Practice for Powering and Grounding Electronic Equipment (IEEE Std 1100-2005). IEEE, 2005.
National Fire Protection Association (NFPA). NFPA 70: National Electrical Code. NFPA, 2023.