Why are transformer oil trays so important?

For legally compliant and correct storage of hazardous substances, oil collection trays for transformers are a necessary and effective solution. They capture leaking insulating oils directly and thus protect water, soil and the environment. These collection systems are usually made of plastic or steel, are available in different sizes and should be checked regularly for leaks and function. Read more here.

How is transformer oil classified by law? 

The Water Resources Act (WHG) in Germany, for example, classifies solid, liquid and gaseous substances as hazardous if they cause permanent or significant damage to the quality of the water.

Oil or used oil is categorised as a particularly severe threat to the environment and to water bodies (WGK = water hazard class 3). Just a few drops of oil pollute many times the amount of water.  

For this reason, transformer operators must provide containment systems such as transformer oil trays.

How dangerous is transformer oil?

Transformer oils based on mineral oil are still predominantly in use today. They are employed for insulation, cooling and heat transfer. Since some components of these insulating oils can be harmful to the environment, professional handling with appropriate equipment is essential – depending on the surrounding conditions.

A safety container in the form of a transformer oil tray is essential to prevent environmental damage.

Older mineral-based transformer oils used prior to 1989 may contain polychlorinated biphenyls (PCBs). These substances can be toxic to both humans and the environment and are not biodegradable. Even modern insulating oils derived from mineral oil carry risks: in the event of overheating or leakage, they can be highly flammable.

• The containment of transformers is crucial in order to prevent environmental contamination caused by insulating oil. 
• Equally, safe disposal must be ensured. 
• The hydrocarbons found in mineral-based transformer oils can cause fires when vapourised or exposed to high temperatures.    

What are the regulations for transformer oil trays?

Legislation stipulates the storage of hazardous substances in several laws, directives and ordinances. These deal with both the general handling of substances hazardous to water and specific regulations regarding transformer oil trays. The following legal frameworks are relevant and interconnected:

• Water Resources Act 
  Governs water resource management and pollution prevention across England and Wales. It forms the legal basis for regulating facilities handling substances hazardous to water. 
• Environmental Permitting (England and Wales) Regulations 
  Consolidates multiple environmental rules, including permits for installations working with hazardous substances. Covers groundwater and surface water protection through containment measures.  

What materials and designs are available for transformer oil trays?

Transformer oil trays are available in various designs:

• Galvanised or painted steel 
• Stainless steel 
• Heavy-duty plastic (e.g. LLDPE) 

Such oil trays can be flexibly adapted to site conditions and transformer size. It is important that they are integrated into the earthing system and installed in accordance with applicable standards.

Maintenance: Check transformer oil trays and insulating oil together

It is recommended to carry out a visual inspection every two years and a detailed inspection of the transformer oil tray by a specialist company every five years, in combination with the insulating oil analysis.

Transformer oil trays as part of a holistic safety concept

Long before major damage becomes visible in transformers, transformer oil analyses provide important indications of possible weak points. That is why the insulating oil in transformers is examined regularly. This is a good opportunity to check the transformer oil trays as well.

Detect leaks early and prevent seepage with oil trays      

Transformer oil trays prevent leaking insulating oil from seeping into the ground, thereby protecting the environment and water bodies. At the same time, the tray serves as an early warning system for the condition of the transformer. Even the smallest leaks can be quickly detected by shimmering oil puddles forming in the tray.

Regular inspection of transformer oil trays for leaks is essential. Ideally, it should be carried out together with the scheduled insulating oil analysis. In addition, simple visual checks at shorter intervals are also advisable.

Specialist companies regularly assess oil trays 

For specialist companies, inspecting oil trays is standard procedure. As an experienced service provider and European expert for both recycled and new insulating oils – as well as for comprehensive transformer services – the service company Electrical Oil Services (EOS^®) offers reliable, all-round maintenance and servicing work.

Our tip: During your next insulating oil maintenance, make sure your transformer oil tray is also inspected! 

Find out more in these blog articles:

• Transformer maintenance: when should you replace the insulating oil in transformers? 
• Valuable tips if you want to have the insulating oil in the transformer changed 
• Laboratory services for insulating oils: This is what you need to look out for

Conclusion: Transformer oil trays are legally required, technically necessary and environmentally beneficial. 

Oil trays not only protect against environmental damage, but also support the early detection of technical defects.

For the operation of transformers and the handling of insulating oil, oil containment systems and their regular inspection are mandatory.

Make sure that the specialist company inspecting the condition of your transformers also includes containment systems such as transformer oil trays in the maintenance work. This includes checking whether the oil trays are integrated into the earthing system. As a specialised company according to the Water Resources Act and other legal frameworks, this work is a matter of course for Electrical Oil Services.

We at EOS work exclusively with trained specialist personnel, strictly adhere to standards and regulations and carry out all work processes professionally and carefully. 

Do you have any questions? We will be happy to advise you personally. Contact us directly:

This blog was first published on November 21, 2023 and updated on June 3, 2025.