Elimination of Overheating of Electrical Panels: Thermographic Control, Detection of Loose Connections, Harmonic Distortions and Load Imbalance

1. Description of the Problem and Scope of Application

Overheating of electrical panels and switchboards is a critical fault that can lead to serious consequences, including fires, equipment damage, unplanned production shutdowns and threats to personnel safety. This manual is intended for technical specialists, reliability engineers and heads of maintenance departments of Ukrainian industrial enterprises for systematic diagnosis and elimination of the causes of overheating.

Symptoms considered:

• Visible darkening or discoloration of insulation and components.
• The smell of burnt insulation or plastic.
• Frequent tripping of circuit breakers without obvious overload.
• Failure or unstable operation of connected equipment.
• Elevated temperature of the body of the electrical panel, detected by touch (CAUTION: dangerous!).

Types of equipment considered:

• Main switchboards (main switchboards).
• Motor control cabinets (MCC).
• DC and AC distribution panels.
• Industrial automation and control cabinets.

Severity Classification:

• Critical: The temperature of the components exceeds +80°C or there are sparks, smoke. Immediate equipment shutdown and troubleshooting are mandatory to avoid fire and catastrophic damage.
• Significant: Temperature +60°C to +80°C. Possible premature aging of insulation, reduced reliability, risk of component failure. Needs to be scheduled for troubleshooting at the next scheduled maintenance.
• Minor: Temperature +40°C to +60°C. Indicates a potential problem that may worsen over time. It is recommended to include in the next preventive maintenance cycle.

2. Safety Precautions

CAUTION: Working with electrical panels poses an increased risk of electric shock, arcing, and thermal burns. Always follow local regulations, DSTU and internal company safety standards.

LOCKOUT/TAGOUT (LOTO): Before any work involving physical contact with electrical components, it is necessary to completely de-energize and apply LOTO procedures according to DSTU EN 50110-1 "Operation of electrical installations". Check the absence of voltage with the voltage indicator!

PERSONAL PROTECTIVE EQUIPMENT (PPE): Mandatory use of dielectric gloves, protective glasses, fire-resistant clothing (protection class according to risk assessment), protective shoes with dielectric soles and a protective helmet with a face shield.

HAZARD OF RESIDUAL ENERGY: After the power is turned off, large capacitors can store dangerous voltages. Always check their discharge before touching.

WORK UNDER VOLTAGE: Work under voltage (for example, thermographic inspection) must be performed exclusively by qualified personnel who have undergone special training, in the presence of written permission (permission order) and in compliance with all safety requirements, in particular, the use of PPE with the appropriate class of protection against arc discharge.

3. Necessary Diagnostic Tools

Effective diagnostics of overheating requires the use of specialized measuring devices. Below is a list of recommended tools:

4. Initial Evaluation Checklist

Before starting a detailed diagnosis, it is necessary to collect as much information as possible about the operating conditions and the history of the malfunction. This checklist will help organize the primary data:

5. Systematic Diagnostic Algorithm

This algorithm is a decision tree that allows you to consistently identify and localize the cause of overheating of the electrical panel. Follow it step by step.

1. Symptom: General or local overheating of the electrical panel.
2. Primary Diagnostics - Thermographic Inspection:
   1. CAUTION: Carry out under working voltage (open the panel door while observing all safety rules and PPE).
   2. Use a thermal imager (eg FLIR T540) with a range of 0°C to 200°C, emissivity set to 0.95 (for most components).
   3. Scan all available switchboard components: circuit breakers, contactors, terminal connections, transformers, cables.
   4. Analysis of results:
      • If hot spots are detected (>60°C): Go to point 3 (Location of Heat Source).
      • If the temperature of all components is normal (<40°C above the ambient temperature): Go to item 6 (Analysis of Power Quality), the cause of overheating may not be purely thermal or manifests itself under other conditions.
3. Locating the Heat Source:
   1. Identify the hottest components. Pay attention to the nature of heat distribution.
   2. Analysis of the nature of the heat:
      • If the heating is localized on one connection (terminal, circuit breaker contact, bus connection): This indicates a weak connection or contamination of the contact. Go to point 4 (Check for Loose Connections).
      • If the entire component heats up (eg circuit breaker body, transformer windings, cable section): This could be an overload or an internal component fault. Go to item 5 (Measurement of Current Loads).
4. Loose Connection Check:
   1. CAUTION: APPLY LOTO before any physical contact!
   2. Visually inspect the suspicious connection: the presence of oxidation, sparking, deformation.
   3. Use a torque wrench (eg 2-30 Nm) to check the tightening torque. Compare with the manufacturer's recommended values ​​(usually listed on the component or in the documentation).
   4. Measure the voltage drop across the load connection (if LOTO is not possible, to be safe): a value >10-20mV indicates increased resistance.
   5. If a loose/oxidized connection is found: Go to Section 8 (Troubleshooting).
   6. If the connection is tightened properly, but the heating persists: Go to point 5 (Measuring Current Loads), this may be a secondary effect or an internal fault of the contact.
5. Measuring Current Loads:
   1. Use a True RMS current clamp (e.g. Fluke 376 FC) to measure the current on all phases (L1, L2, L3) and, if possible, on the neutral conductor.
   2. Compare the measured values ​​with the rated currents of the components (circuit breakers, cables) and with the design values.
   3. Analysis of the results:
      • If the current on one or more phases exceeds the nominal one by more than 10%: This is an overload. Go to Section 8 (Troubleshooting) to clear the overload.
      • If the phase currents are significantly different (>10% difference between phases): This is a load imbalance. Go to point 7 (Load Imbalance Analysis).
      • If the currents are normal, but the overheating is significant: This may indicate harmonic distortion or an internal component failure. Go to point 6 (Analysis of Power Quality).
6. Power Quality Analysis (Harmonic Distortions):
   1. CAUTION: Measurements are performed under voltage with appropriate PPE.
   2. Connect a power quality analyzer (such as a Fluke 435 II) to the input terminals of the switchboard.
   3. Measure the current (THD-I) and voltage (THD-U) total harmonic distortion for each phase. Pay attention to the amplitudes of individual harmonics (3rd, 5th, 7th, etc.).
   4. Analysis of results:
      • If THD-I exceeds 5% (according to DSTU EN 50160 and EN 61000-3-2/3-4) and overheating is observed: This is a significant cause of overheating. Go to Section 8 (Troubleshooting).
      • If THD-I is OK but overheating is still present: Consider internal damage to a component (such as a circuit breaker) or insufficient ventilation. Go to point 7 (Load Imbalance Analysis) or perform additional isolation tests.
7. Load Imbalance Analysis:
   1. Use a current clamp or a power quality analyzer to accurately measure the currents on each phase (L1, L2, L3).
   2. Calculate the coefficient of current imbalance: $\text{Imbalance}=\frac{\text{max}-\text{ser}}{\text{ser}}\times 100\text{\%}$ , where max is the maximum phase current, ser is the average phase current.
   3. Analysis of the results:
      • If the imbalance of currents exceeds 10% (according to DSTU EN 60034-1 for three-phase motors), and overheating is observed: This is a significant reason. Go to Section 8 (Troubleshooting).
      • If the imbalance is normal, but no other reasons are found: Carefully check the ventilation, the possibility of external heating or hidden internal defects of the components (for example, damaged insulation of the windings).

6. Malfunction-Cause matrix

This matrix systematizes the relationship between symptoms, probable causes, diagnostic methods, and expected outcomes. The probability of causes is ranked from 1 (highest) to 3 (lowest).

7. Root Cause Analysis for Each Malfunction

7.1. Weakened or Oxidized Compounds

Detailed description: Connections in switchboards, especially threaded ones (bolt, screw terminals), can weaken or oxidize over time. The main causes are vibration from running equipment, frequent heating/cooling cycles, corrosion (especially in humid or aggressive environments) and insufficient initial tightening torque during installation. The increased transient resistance at the place of the weakened contact leads to a significant release of heat according to the Joule-Lenz law ($P=I^{2}R$. Even a slight increase in resistance (a few milliohms) at high currents can cause significant local overheating.

How to confirm:

• Thermographic inspection will reveal a localized hot spot (temperature can exceed 100°C) on the joint.
• A visual inspection may show traces of metal discoloration, melting of insulation, traces of sparking, soot around the contact.
• Measure the voltage drop under load: If the voltage drop across the connection exceeds 50 mV, this indicates a problem.
• Use a torque wrench to check the tightening torque. If it is significantly lower than recommended (for example, IEC 60947-1 for low-voltage equipment), this confirms attenuation.
• Measure the connection resistance with a milliohmmeter: values ​​greater than 10 mΩ are suspect.

What damage it causes if not removed: Further deterioration of the contact leads to sparking, which is a direct risk of fire and explosion. High temperature destroys the insulation of cables and components, which can lead to short circuits or ground faults, total equipment failure and prolonged downtime.

7.2. Current overload

Detailed description: An overload occurs when an electrical component (cable, circuit breaker, contactor) operates with a current that exceeds its rated or allowable continuous current. This may be the result of: installation of new, more powerful equipment without modernization of the distribution network; technological process changes that require higher productivity; malfunctions of connected equipment (for example, electric motor jamming, which leads to an increase in current consumption); or even errors in design and calculations when installing the system.

How to confirm:

• Current measurement with True RMS current clamps on each phase. Compare the measured values ​​with the rated currents indicated on the circuit breakers, cables and other components. An excess of 10% or more indicates overload.
• Analysis of data logs (if available) from energy monitoring systems.
• A thermographic inspection will show uniform overheating of the entire overloaded component or cable section.

What damage it causes if left untreated: Constant overheating significantly shortens the life of components. Cable insulation ages and loses its dielectric properties, which increases the risk of short circuits. Circuit breakers can trip frequently or, in the worst case, fail without tripping, leaving the system unprotected. Overheating also leads to increased energy losses.

7.3. Harmonic Distortions

Detailed description: Harmonic distortions in the electrical network are currents and voltages whose frequencies are multiples of the main frequency (50 Hz in Ukraine). They are generated by non-linear loads such as inverters, frequency converters, switching power supplies, LED lights, UPS systems, computers and other modern electronic equipment. Harmonics do not perform useful work, but increase the total current in the network (especially in the neutral conductor of three-phase systems) and cause additional losses in the form of heat in transformers, cables and motors. This leads to overheating, even if the RMS current of the phases does not exceed the nominal.

How to confirm:

• Using a power quality analyzer (for example, Sonel PQM-710) to measure the total harmonic distortion current (THD-I) and voltage (THD-U) according to DSTU EN 50160 and EN 61000-3-2/3-4.
• A THD-I value >5% is considered significant and requires attention, especially if low-order harmonics (3rd, 5th) are present.
• A thermographic inspection will show an increased temperature of transformers, cables, especially the neutral conductor, which is not proportional to the active load.

What damage it causes if not eliminated: Harmonics accelerate the aging of insulation, cause additional vibrations and noise in electric motors, can cause false activation of protective devices, malfunctions of sensitive electronic equipment. Overheating of transformers due to harmonics can lead to their failure, and in the neutral conductor - to its burnout and considerable danger.

7.4. Load imbalance

Detailed description: A load imbalance in a three-phase system occurs when the currents or voltages in different phases are significantly different. The main reason is the uneven distribution of single-phase loads between the three phases. It can also be caused by a malfunction of one of the phases, a break or damage to the cable, or an internal malfunction of the three-phase consumer. Current imbalance causes uneven heating of phase conductors, additional losses in three-phase motors and transformers, reduces their efficiency and reliability.

How to confirm:

• Measure currents and voltages on all three phases using current clamps or a power quality analyzer.
• Calculation of the coefficient of imbalance of currents and voltages. According to DSTU EN 60034-1, voltage imbalance for electric motors should not exceed 1-2%. A current imbalance >10% is critical.
• A thermographic inspection will show that one or two phases in a multiphase system are significantly hotter than the others.

What damage it causes if not eliminated: Load imbalance leads to overheating of individual phase conductors and windings of electric motors (even at the rated total current), which significantly shortens their service life, reduces efficiency and causes additional vibrations. In transformers, imbalance also causes overheating and additional losses.

8. Step-by-Step Troubleshooting Procedures

8.1. Removal of Weakened or Oxidized Compounds

1. CAUTION: USE THE FULL LOTO PROCEDURE! Check that there is no voltage.
2. Disassemble the connection that overheats.
3. Thoroughly clean the contact surfaces from oxidation, dirt and soot using fine-grained sandpaper or special contact cleaning products. Make sure the surfaces are smooth and clean.
4. Check the integrity of the conductor and its insulation at the connection point. If necessary, clean the end of the conductor or replace it.
5. Assemble the joint, making sure that all washers (flat, spring) are installed correctly.
6. Tighten the threaded connections with a torque wrench to the torque recommended by the manufacturer (for example, for 2.5 mm² terminals - 0.8-1.2 Nm; for power busbars - 10-25 Nm, see the specification).
7. Check the resistance of the new connection with a milliohmmeter. The value should be less than 10 mΩ, ideally less than 1 mΩ.
8. After power is restored (after removing the LOTO), conduct a repeat thermographic inspection to verify the elimination of overheating.

8.2. Elimination of Current Overload

1. CAUTION: APPLY THE FULL LOTO PROCEDURE before making any changes to the chain.
2. Identify the source of the overload: measure the currents of all connected consumers.
3. Option A (Reduce load): If possible, reduce the workload of the equipment or redistribute consumers to other, less loaded lines.
4. Option B (Upgrading): If load reduction is not possible, the system must be upgraded:
   • Replace circuit breakers and other protective devices with a rating corresponding to the actual peak current, after confirming that the cables and busbars are of sufficient cross-section.
   • Replace the cables and busbars with ones with a larger cross-section if the current conductors do not meet the new rating of automatic switches (according to DSTU IEC 60364 "Electrical installations of buildings").
   • Install additional distribution lines to evenly distribute the load.
5. Check the new currents after the changes and perform a thermographic inspection.

8.3. Elimination of Harmonic Distortions

1. CAUTION: Working with harmonic filters may require special skills and PPE.
2. Identify the main sources of harmonics in your network (eg frequency converters, UPS, power supplies).
3. Setting harmonic filters:
   • Passive filters: Adjust harmonics of a certain order. Effective for stable non-linear loads.
   • Active filters: More flexible, can compensate harmonics of different orders and dynamically adapt to load changes.
4. The use of transformers with a special K-factor, which are designed to work in conditions of high harmonic currents.
5. Use of equipment with a low level of harmonics (for example, frequency converters with an active power factor corrector).
6. After installing the filters, re-analyze the power quality with the analyzer to confirm that the THD-I has decreased to acceptable values ​​(eg <5%).

8.4. Elimination of Load Imbalance

1. CAUTION: USE THE COMPLETE LOTO PROCEDURE to reconnect safely.
2. Determine which single-phase loads are connected to each phase.
3. Redistribute single-phase consumers between phases L1, L2, L3 so that the currents on each phase are as close as possible. Aim for a current difference of no more than 5-10%.
4. Check the serviceability of three-phase consumers (for example, electric motors), whether there are no inter-turn short circuits or breaks that can cause imbalance.
5. After reconnecting and restoring power, remeasure phase currents with current clamps and perform thermographic inspection to confirm elimination of unbalance and overheating.

9. Precautions

Preventive measures are critical to ensure long-term and reliable operation of electrical systems. Implementing regular monitoring and scheduled maintenance can avoid most overheating problems.

10. Spare Parts and Components

Availability of the necessary spare parts is critical for quick and efficient troubleshooting and minimizing downtime. Below are typical components to have in stock.

All necessary spare parts and components can be found in the UNITEC-D e-catalogue: www.unitecd.com/e-catalog/

11. Links

• DSTU EN 50110-1:2017. Operation of electrical installations.
• DSTU EN 60947-1:2017. Switching equipment and low-voltage control equipment. General rules.
• DSTU EN 50160:2014. Characteristics of power supply voltage in public electrical networks.
• DSTU EN 61000-3-2:2017. Electromagnetic compatibility (EMC). Part 3-2. norms Current harmonic emissions standards (for equipment with an input current of up to 16 A).
• DSTU EN 61000-3-4:2017. Electromagnetic compatibility (EMC). Part 3-4. norms Limitation of the emission of current harmonics for equipment with a rated current of more than 16 A per phase (for public low-voltage systems).
• DSTU EN 60034-1:2014. Electric rotary machines. Part 1. Nominal parameters and operating characteristics.
• ISO 18436-7:2014. Condition monitoring and diagnostics of machines - Requirements for qualification and assessment of personnel - Part 7: Thermography.
• Appropriate OEM operation and maintenance manuals for specific equipment.
• Other UNITEC-D maintenance manuals.