Data Centres
High-resistance connections can affect critical electrical joints, terminations and distribution equipment within data centres.
Discover MoreHigh-Resistance Electrical Connections Identified by Thermal Imaging
- ✔ PCN/ITC L2+
- ✔ ISO 18434-1
- ✔ Fully insured
- ✔ UK-wide
Understanding High-Resistance Electrical Connections
High-resistance electrical connections are frequently identified during electrical thermal imaging surveys. They can develop at cable lugs, crimped terminations, bolted joints, palm plates, transformer bushings and connections throughout low-voltage and high-voltage systems.
Although a loose connection may create additional resistance, high-resistance conditions can also result from corrosion, oxidation, contamination, damaged conductors, poor crimping, deteriorated mating surfaces or age-related degradation. The external appearance may offer no reliable indication of the electrical or thermal condition.
Our electrical thermal imaging surveys provide a non-invasive way to compare connection behaviour while equipment remains energised and operating under representative load. This page explains how high-resistance connections develop, how they may appear thermally, and why correct diagnosis requires more than identifying the hottest component.
The operational significance varies considerably according to the asset. A deteriorating cable lug in final distribution and a high-resistance joint on a 132kV current transformer may share a similar failure mechanism, but the consequences of failure, access constraints and appropriate maintenance response can be very different.
Effective assessment therefore considers the location and distribution of heat, electrical load, comparable phases or connections, equipment construction and potential failure consequences. This wider context helps distinguish a genuine high-resistance condition from normal load-related heating and supports proportionate prioritisation.
For a wider overview of related anomalies, visit our Common Electrical Faults Identified by Thermal Imaging guide. High resistance can also be associated with loose connections, which are covered separately in our Loose Electrical Connections guide.
Page Contents
- What Are High-Resistance Connections?
- Why High-Resistance Connections Generate Heat
- Thermal Imaging Examples
- Causes, Indicators, Equipment and Risks
- Where High-Resistance Connections Occur
- Corrective Action and Follow-Up
- Why Specialist Thermal Interpretation Matters
- Why Choose Red Current
- Industry Applications
- Frequently Asked Questions
What Are High-Resistance Connections?
Electrical current should pass through a sound connection with very low resistance. When the interface between conductive surfaces deteriorates, the effective current path can become restricted and additional energy may be dissipated as heat.
A high-resistance condition can occur even where a connection remains mechanically secure. Oxidation, corrosion, contamination, damaged strands, poor crimping or degraded contact surfaces may all impair conductivity without producing an obvious visual defect.
The significance of the condition is established from the thermal pattern, loading, comparison with similar connections and the function of the affected asset. Safe isolation and physical investigation by an appropriately competent electrical contractor may then be required to confirm the underlying cause.
Why High-Resistance Connections Generate Heat
Restricted Current Path
When contact quality deteriorates, current is forced through a reduced or degraded conductive interface. The resulting increase in resistance can produce localised heating at the affected joint.
Progressive Surface Degradation
Heat can accelerate oxidation and deterioration of conductive surfaces. If the cause remains unresolved, resistance and temperature may continue to increase under similar loading.
Why Similar Defects Can Look Different
The apparent temperature and shape of the anomaly are influenced by load, component geometry, thermal mass, cooling and the position of the defect within the assembly. This is why comparison and electrical context are essential.
Thermal Imaging Examples of High-Resistance Connections
High-resistance faults can present across both low-voltage and high-voltage equipment. The two examples below add transformer-bushing and corrosion-related isolator defects to the cable-lug and current-transformer examples shown above.
Important: These examples show abnormal thermal behaviour across cable terminations, current-transformer connections, transformer bushings and corroded isolator palm plates. They do not provide a universal temperature threshold. Meaningful assessment requires suitable loading, comparison with similar assets, equipment knowledge and consideration of operational consequences.
High-Resistance Connection Characteristics
Common Causes
- Oxidation and corrosion
- Surface contamination
- Poor crimping or damaged conductors
- Inadequate joint preparation
- Deteriorated mating surfaces
- Loose or inadequately tightened joints
- Mechanical wear and ageing
Typical Thermal Indicators
- Localised heating at a joint or termination
- One connection hotter than comparable connections
- Heat concentrated at the conductive interface
- Abnormal phase-to-phase temperature differences
- Increasing differential during repeat inspections
Affected Equipment
- Cable lugs and crimped terminations
- Current transformers and voltage transformers
- Transformer bushings
- Isolator palm plates
- Busbar joints
- Switchgear and substations
- Switch fuses and disconnectors
Potential Risks
- Accelerated material degradation
- Electrical arcing
- Connection or equipment failure
- Loss of critical electrical supply
- Unplanned outages
- Fire risk
- Emergency repair and replacement costs
Concerned About a Suspected High-Resistance Connection?
Red Current can assess live electrical equipment under representative load, provide clear thermal and visual evidence, and deliver an independently reviewed report with prioritised recommendations. We also support electrical testing companies that require a specialist thermography partner.
Where High-Resistance Connections Commonly Occur
High-resistance conditions can develop wherever electrical current passes through bolted, crimped or mating conductive surfaces. Common locations include cable lugs, busbar joints, transformer bushings, instrument-transformer connections, switchgear contacts, isolator palm plates and outdoor substation connections.
The same underlying increase in resistance can create different thermal patterns. A cable lug may show concentrated heating at the crimp or palm, while a bushing or bolted substation connection may transfer heat into a much larger assembly. Equipment knowledge is therefore essential when tracing the likely current path and fault location.
The four examples on this page span low-voltage cable termination equipment and critical 33kV and 132kV assets. Together they demonstrate that high resistance is a cross-system condition rather than a defect confined to one component type.
Corrective Action and Follow-Up
Thermal imaging identifies where abnormal connection behaviour warrants further attention; it does not replace safe isolation, physical examination and remedial work by an appropriately competent electrical contractor. Corrective action may include cleaning or preparing mating surfaces, replacing damaged conductors or lugs, renewing corroded components, correcting mechanical strain or reinstating the joint in accordance with the equipment manufacturer’s requirements.
Where practicable, a follow-up thermal inspection under suitable operating load can verify that the repaired connection no longer exhibits the previous abnormal pattern. If representative loading is unavailable, the finding may require continued monitoring until meaningful verification can be completed.
Need a Survey or Independent Verification?
Red Current can provide a specialist electrical thermal imaging survey or follow-up verification inspection under suitable operating load. Our electrically qualified, ITC/PCN certified thermographers provide clear thermal and visual evidence, independently reviewed reporting and prioritised recommendations, while your appointed electrical contractor or in-house team remains responsible for safe isolation and remedial work.
Why Specialist Thermal Interpretation Matters
Not Every Hot Connection Is Defective
A sound connection carrying greater current, receiving transferred heat or operating in a different cooling environment may be hotter than adjacent equipment. Representative load data and suitable comparisons are necessary before classifying the condition.
Not Every High-Resistance Fault Appears Extremely Hot
A developing resistance issue may show only a modest differential when the circuit is lightly loaded. Asset criticality, likely deterioration and failure consequences may still warrant investigation or monitoring.
Resistance Does Not Reveal Its Own Cause
Thermography may identify the location and thermal significance of abnormal resistance, but safe physical investigation may be needed to distinguish looseness, corrosion, contamination, poor crimping or damaged conductive surfaces.
Interpretation and Reporting Create the Value
The value of an electrical thermal imaging survey lies in turning thermal evidence into a defensible maintenance decision. Red Current’s assessments draw on electrical expertise, thermography certification, structured review and an in-house knowledge base of component operating temperatures developed from years of reporting data and millions of thermal images.
Specialist Support for Electrical Testing Companies
Electrical testing companies are frequently asked to include thermal imaging alongside fixed-wire testing, condition reporting or planned maintenance. Red Current can deliver the specialist thermographic survey, analysis, priority classification and reporting while the electrical contractor retains the client relationship and responsibility for remedial work.
Why Choose Red Current for Electrical Thermography?
Realising the full value of an electrical thermal imaging survey depends on the competence of the thermographer, the quality of the inspection process and the clarity of the final report. Red Current combines electrical knowledge, certified thermography expertise and structured quality assurance to provide findings that can be understood, prioritised and acted upon.
Qualified Thermographers
Our electrical thermal imaging surveys are undertaken by electrically qualified, ITC/PCN certified thermographers. These recognised certification schemes provide structured training and assessment in infrared thermography, while our electrical qualifications and field experience support safe, technically informed inspection of live electrical systems. Thermographer competence matters because image capture, measurement, interpretation and reporting must be considered together.
Read more about why ITC/PCN thermography certification and surveyor competence matter.
ISO-Aligned Survey and Reporting
Our survey and reporting processes are aligned with ISO 18434-1, supporting a consistent approach to inspection, analysis and communication of findings. Reports are prepared to give maintenance teams clear evidence, appropriate context and practical priorities.
See our guidance on electrical thermal imaging standards, reporting and survey requirements.
Reviewed, Actionable Reporting
Thermal images alone do not provide a maintenance strategy. Our reporting process turns observations into documented findings with supporting thermal evidence, priority classifications and recommendations that can be used by facilities teams, insurers and electrical contractors.
Find out whether an electrical thermal imaging report can support insurance requirements.
Experience Across LV and HV Systems
High-resistance conditions can occur at compact cable terminations, high-current busbar joints, transformer bushings and outdoor substation connections. Red Current delivers electrical thermography across commercial, industrial and high-voltage environments, helping ensure each anomaly is assessed in the correct asset and operational context.
Explore our common electrical faults guide and high-voltage thermal imaging surveys.
Specialist support without competing for remedial work: Red Current can provide the thermographic survey, analysis and report while the client’s appointed electrical contractor or in-house electrical team completes any required investigation and remedial work.
Industries Commonly Affected by High-Resistance Connections
High-resistance connections can develop across almost every electrical environment. Their operational impact is particularly significant where continuity, life safety, production or critical power systems depend on reliable electrical joints and terminations.
Manufacturing Facilities
High-resistance connections can affect critical electrical joints, terminations and distribution equipment within manufacturing facilities.
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High Voltage Substations
High-resistance connections can affect critical electrical joints, terminations and distribution equipment within high voltage substations.
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Hospitals & Healthcare Facilities
High-resistance connections can affect critical electrical joints, terminations and distribution equipment within hospitals & healthcare facilities.
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Distribution Centres
High-resistance connections can affect critical electrical joints, terminations and distribution equipment within distribution centres.
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Food Manufacturing Facilities
High-resistance connections can affect critical electrical joints, terminations and distribution equipment within food manufacturing facilities.
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Commercial Offices
High-resistance connections can affect critical electrical joints, terminations and distribution equipment within commercial offices.
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Schools, Colleges & Universities
High-resistance connections can affect critical electrical joints, terminations and distribution equipment within schools, colleges & universities.
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Shopping Centres & Retail Parks
High-resistance connections can affect critical electrical joints, terminations and distribution equipment within shopping centres & retail parks.
Discover MoreFrequently Asked Questions
High-resistance conditions can develop through corrosion, oxidation, contamination, damaged conductors, poor crimping, deteriorated mating surfaces, inadequate joint preparation or loss of connection integrity.
Yes. Increased resistance commonly produces localised abnormal heating under electrical load. Reliable assessment requires comparison with similar connections, suitable loading information and knowledge of the affected equipment.
No. A mechanically secure joint can still develop excessive resistance because of corrosion, contamination, poor surface contact, damaged conductors or an inadequate crimp. Thermography identifies abnormal thermal behaviour but further investigation may be required to confirm the cause.
Yes. Continued heating can damage insulation and components, accelerate surface degradation and increase the likelihood of arcing, equipment failure or fire.
No. Temperature is influenced by electrical load, equipment design, cooling and the stage of deterioration. Priority also depends on asset criticality and the consequences of failure.
Yes. High-resistance conditions can affect transformer bushings, current-transformer connections, isolator palm plates, busbar joints and other high-voltage substation assets.
Prioritisation considers thermal behaviour, loading, component type, asset criticality, possible failure mechanisms and operational or safety consequences rather than relying on temperature alone.
Capturing a thermogram is only one part of the survey. Specialist thermographers interpret loading, thermal patterns, equipment construction and failure mechanisms, then communicate findings through consistent reporting and actionable priorities.
For broader survey questions, visit our Electrical Thermal Imaging Survey FAQs.
High Resistance Is Common. Correct Diagnosis Is Not.
High-resistance connections are a common electrical anomaly, but their significance cannot be judged simply by locating the hottest object. Suitable operating conditions, comparative analysis, equipment knowledge and an understanding of failure consequences are essential if thermal findings are to support sound maintenance decisions.
Red Current provides specialist electrical thermography for end users, facilities teams, insurers and electrical testing companies throughout the UK. Contact us to request pricing, obtain a sample report or discuss a subcontract survey requirement.
