PCB testing procedures at a glance: How to deal with PCB transformers

Polychlorinated biphenyls (PCBs) in transformer oils are more relevant today than ever before. Particularly in older installations, operators and technical managers face the challenge of testing transformers for PCBs, classifying them correctly and acting in full legal compliance. Read on to learn which PCB testing procedures are available, how they are applied, which regulatory limit values apply and how results are translated into operational decisions.

“Electrical Oil Services supports transformer operators throughout the entire process – if required, from initial sampling and PCB analysis in the laboratory through to the technical interpretation of results and the derivation of necessary measures.”

– Dr Paulina Nieves, Head of the EOS^® Laboratory in Hamburg

Why are PCB testing procedures indispensable for transformer operators?

Due to their toxic, carcinogenic and environmentally hazardous properties, PCBs are subject to strict regulation. PCBs comprise a group of 209 different congeners of chlorinated biphenyls, some of which exhibit differing levels of toxicity. The key regulatory framework includes both the former EU Directive 96/59/EC on the management of PCB-containing equipment and the currently applicable requirements of the EU POP Regulation (persistent organic pollutants), which prohibits the manufacture, use and placing on the market of PCB-containing substances and governs their disposal. (source: European Commission – PCBs and PCTs).

Under these regulations, a clear threshold applies: 50 ppm (0.005%) PCBs in transformer oil. Equipment or oils exceeding this value are considered PCB-contaminated and are subject to specific legal requirements regarding removal or treatment.

According to the POP Regulation, all PCB-containing liquids in electrical equipment (transformers, capacitors, etc.) had to be identified and removed or decontaminated by the end of 2025 at the latest if they contained more than 0.005% PCBs.

Important for practical application:
👉 Legal requirements do not automatically require disposal of the entire transformer, but primarily the proper removal or treatment of the PCB contamination.

PCB testing procedures provide clarity for PCB transformers

To act in a legally compliant and technically appropriate manner, PCB testing procedures are the central decision-making basis. They form the interface between regulatory obligations and operational implementation. PCB test results allow PCB-contaminated transformer oils to be correctly classified and support the planning of appropriate measures such as cleaning, decontamination or decommissioning.

What must a PCB testing procedure deliver?

A PCB testing procedure is used to reliably determine the total PCB content in transformer oil. Results are expressed in ppm (parts per million) or mg/kg and form the basis for:

• the regulatory classification of the transformer,
• decisions regarding continued operation, decontamination or decommissioning,
• and the required documentation for authorities.

Key requirements include:

• representative sampling,
• a suitable analytical method,
• and technically sound interpretation of results.

Also of interest:

Step 1: Representative sampling

The quality of any PCB testing procedure begins with sampling. Errors at this stage can lead to incorrect measurement results and, consequently, to wrong decisions.

Established best practice includes:

• sampling directly from the transformer,
• use of suitable, PCB-free sample containers,
• avoidance of cross-contamination,
• documentation of sampling location, date and operating condition.

For compliant sampling, reference should be made to internationally recognised standards such as IEC 61619 or EPA Method 8082A to ensure reproducibility of results.

Guidance on proper transformer oil sampling is provided in this interview:

Transformer: Representative insulating oil sampling in 10 steps

Step 2: PCB testing procedures in the laboratory

Gas chromatography (GC-ECD) – standard method: Gas chromatography with an electron capture detector (GC-ECD) is the most commonly used PCB testing procedure. It enables:

• sensitive detection of PCBs in the ppm range,

• reproducible results,

• clear comparability with regulatory limit values.
  

Advanced analysis using GC-MS: In more complex cases or when values are close to regulatory thresholds, gas chromatography–mass spectrometry (GC-MS) is used as a complementary method. It allows more detailed differentiation of individual PCB compounds and provides additional verification of results.

GC-MS is frequently used to confirm and identify individual PCB congeners, particularly where regulatory requirements or more in-depth toxicological assessments are required.

These analyses should ideally be carried out in laboratories with appropriate quality management systems. At the EOS^® laboratory, PCB analyses are performed as part of a comprehensive insulating oil analysis portfolio, with standardised methods, documented testing procedures and transparent reporting at the forefront.

Step 3: Limit values, classification and assessment

For operational practice, the following limit values are decisive:

Central threshold:

< 50 ppm PCBs in transformer oil
→ the transformer is no longer considered PCB-contaminated from a regulatory perspective
→ continued operation is generally possible
→ documentation and verification obligations remain

≥ 50 ppm PCBs in transformer oil
→ the transformer is considered PCB-contaminated
→ measures are required and the insulating oil must be disposed of in accordance with the law

In accordance with national and EU-wide regulations, transformers with PCB concentrations of ≥ 50 ppm must be classified as PCB-contaminated and directed to appropriate disposal pathways; this threshold is defined in the POP Regulation.

Crucially, measurement results must be interpreted in the context of the specific installation, its history and potential follow-up measures. Laboratories such as the EOS^® laboratory support transformer operators in assessing PCB test results as part of a structured evaluation and decision-making process.

Step 4: From analysis to action – what follows a PCB testing procedure?

A PCB testing procedure does not usually end with a laboratory report. What matters is how results are translated into concrete measures, properly documented and made traceable over the long term.

If a PCB testing procedure indicates values above 50 ppm, the course of action is clearly defined by law:

PCB-contaminated insulating oil above 50 ppm must be disposed of. New or regenerated, PCB-free insulating oil is then filled into the transformer.

Even after an oil change, PCB contamination of solid components (e.g. paper, resins or metal surfaces) may still occur, which is why follow-up investigations are advisable. This phenomenon is well known and must be considered when aiming for comprehensive decontamination.

It is therefore important to note that a transformer may still contain PCBs after an insulating oil change, as PCBs can accumulate in solid materials inside the equipment. For this reason, PCB testing procedures are used not only to demonstrate compliance with limit values, but also preventively at lower concentrations. Follow-up samples and analyses are recommended to assess the effectiveness of the oil change.

Safety when handling PCB-contaminated transformers

When working with PCB-contaminated transformers and insulating oils, occupational health and safety is of the highest priority. PCBs can be absorbed through skin contact or inhalation and pose a serious health risk. As persistent organic pollutants, PCBs are of particular concern due to their carcinogenic and bioaccumulative properties.

In practice, standardised protective measures are therefore essential. These include the use of appropriate personal protective equipment (PPE) such as protective clothing, gloves and respiratory protection, as well as adequate ventilation when working on transformers. Particular care should be taken not to inhale vapours and to avoid direct contact with PCB-contaminated media.

Especially when dealing with PCB-contaminated transformers, structured documentation of analysis results, measures taken and follow-up tests plays a central role. Measurement results, limit values, actions performed and time-based developments must be fully traceable at all times – whether for internal decision-making, audits or regulatory requirements.

Learn more in this interview about the concrete benefits of documentation provided by Electrical Oil Services:

EOS^® database: Making sound decisions in transformer management

Do you have questions regarding the interpretation of your PCB analysis results or the next steps? Our experts will be happy to support you.

Conclusion: PCB testing procedures provide clarity and operational certainty

PCB testing procedures are a central element of technical and regulatory asset management. They enable transformers and their insulating oils to be correctly classified, targeted measures to be implemented and continued operation to be ensured wherever this is technically and legally possible.

In Europe, transformer oils containing more than 50 ppm PCBs had to be removed and properly disposed of by the end of 2025 at the latest. Since the expiry of this deadline, operation above this threshold is no longer permitted.

In addition to PCB analyses, further insulating oil analyses and condition assessments are incorporated to provide a holistic view of transformer condition. The objective is not only regulatory compliance, but also to safeguard operational reliability and extend asset service life wherever possible.

An overview of our services can be found here:

EXPERTISE, SAFETY AND TECHNOLOGY FOR INSULATING OILS AND TRANSFORMERS