1. Problem description and Scope

Overheating in electrical distribution cabinets poses a critical risk to business continuity and fire safety in industrial environments. This defect is manifested by increased ambient temperatures in the cabinet, odor of ozone or burnt insulation material, and unexplained tripping of circuit breakers. This guide is aimed at maintenance technicians and reliability engineers responsible for diagnosing and mitigating thermal anomalies in low voltage panels (up to 1000V AC).

SAFETY WARNING
WORK ON UNDERVOLTAGE PANELS IS VERY DANGEROUS.

Lockout/Tagout (LOTO) is mandatory for all work on components.

Personal Protective Equipment (PPE): Wear arc-resistant clothing (ATPV ≥ 8 cal/cm²), insulated gloves (class 0 or higher), and a face shield.

Take stored energy into account (capacitors, UPS systems).

3. Required Diagnostic Tools

Tool	Specification	Goal
Thermal camera	Resolution ≥ 160x120, temperature range up to 300°C	Hotspot detection
True RMS Multimeter	CAT III 1000V / CAT IV 600V	Measuring voltage and resistance
Current clamp	True RMS, peak current measurement capability	Load measurement per phase
Power Quality Analyzer	Class A (IEC 61000-4-30)	Detection of harmonics and imbalance

4. Initial Assessment Checklist

Observe	Action
Ambient temperature	Measure temperature outside the cabinet versus inside.
Smell/Visual	Check for discoloration, melted insulation or odor.
Tax history	Check recent process load changes.

5. Systematic Diagnosis Flowchart

Visual inspection and Thermography (under load):
- Spot hotspots (> 20°C above ambient)?
  - YES: Identify component (terminal, circuit breaker, fuse).
    - Clamp? Check tightening torque (see table 8).
    - Interrupter? Check for wear/contamination.
  - NO: Go to step 2 (Load measurement).
Load Measurement and Imbalance:
- Is the current imbalance between the phases > 10%?
  - YES: Redistribute burdens (Root Cause: Imbalance).
  - NO: Go to step 3 (Harmonics).
Harmonic Analysis:
- Is the THD-I (Total Harmonic Distortion - Current) > 15%?
  - YES: Investigate non-linear loads (VFDs, switching power supplies).
  - NO: Check ventilation and environmental conditions.

6. Fault-Cause Matrix

Symptom	Probable Cause	Test	Expected result if confirmed
Hotspot under threat	Loose connection	Thermography / Visual	Temperature drops after tightening
Global heat	Overload	Current clamp measurement	Current > rated value
Brummen/Heat	Harmonics	Power Quality Analyzer	High THD-I value
Component error	Internal wear	Voltage drop measurement	Voltage drop across component > 50mV

7. Root Cause Analysis

7.1 Loose connections

Thermal cycling (expansion/contraction) can loosen clamp connections. This increases contact resistance, leading to I²R losses and extreme heat. Danger: Can lead to arcing and fire.

7.2 Imbalance and Overload

An imbalance in the phases causes unnecessary current in the neutral conductor and additional heat development in components. Overloading above the rated current (In) of components shortens the lifespan exponentially according to the Arrhenius equation.

8. Step by Step Resolution

Perform LOTO.
Loose connections: Inspect all terminals. Use a torque wrench according to the manufacturer's specifications (e.g. M6: 3-4 Nm). Replace discolored clamps.
Replacement: If any component (breaker/relay) shows internal damage, replace it with an identical type (see section 10).

9. Preventive Measures

Cause	Prevention	Frequency
Loose connections	Periodic retightening (torque wrench)	Annually
Hot spots	Thermographic inspection	Semi-annually

10. Spare parts

Description	Specification	Category
Industrial clamp	Screw terminal (e.g. 2.5-16mm²)	Connection technology
Circuit breaker	According to IEC 60947-2	Protective equipment

For specific components, see our e-catalog: https://www.unitecd.com/e-catalog/

11. References

IEC 60947: Low-voltage switchgear and controlgear assemblies
NEN 3140: Operation of electrical installations
ISO 18434-1: Thermography for condition monitoring