As a supplier of epoxy bushings, I often get asked a straightforward question by engineers, procurement specialists, and fellow industry partners: “What are the standards that epoxy bushings have to meet?” It’s a question that cuts to the heart of why these components matter so much—they’re the quiet workhorses of transformers, switchgear, and electrical panels, keeping high-voltage power where it belongs (inside the equipment) and letting it flow where it needs to go. Spend any time in the power distribution sector, and you’ll know that a bushing that doesn’t meet the right standards isn’t just a subpar part—it’s a risk. Over the years, I’ve seen firsthand how adhering to these standards separates reliable, long-lasting epoxy bushings from ones that fail prematurely, leading to costly downtime, safety hazards, and frustrated teams. Today, I want to break down what those standards actually look like, why they exist, and how they shape the epoxy bushings that we design and supply for our customers.
First, let’s ground this in what an epoxy bushing is, because not everyone who asks about standards starts with that foundation. An epoxy bushing is an insulating component that passes a current-carrying conductor through a grounded barrier—say, the steel wall of a transformer tank or a metal electrical panel. Made from epoxy resin (often reinforced with fiberglass or other materials for strength), it replaces older, less durable options like porcelain, offering better resistance to thermal stress, mechanical impact, and moisture. As a supplier, our job is to make sure every epoxy bushing we ship doesn’t just fit the equipment, but also meets the strict industry rules that govern performance and safety. To give you a sense of the range, we manufacture everything from low-voltage (LV) options for small switchboards to high-voltage models for large power transformers, all aligned with global standards. For context, you can explore our full line here: Epoxy Resin Cast Bushing
Let’s start with the most fundamental set of standards: those set by international and national standards bodies. The two biggest players here are the International Electrotechnical Commission (IEC) and the Institute of Electrical and Electronics Engineers (IEEE), along with national bodies like the American National Standards Institute (ANSI) in the U.S. and the Deutsches Institut für Normung (DIN) in Germany. These groups don’t make rules out of thin air—they compile decades of field data, lab testing, and best practices to ensure that epoxy bushings work consistently across different climates, voltage levels, and applications.
Take IEC 60137, for example. This is the core standard for bushings for alternating-current systems above 1,000 volts, which covers almost all medium and high-voltage epoxy bushings. It dictates everything from the minimum dielectric strength (how well the epoxy resists electrical breakdown) to the maximum temperature the bushing can handle during normal operation and overloads. IEEE has a parallel standard, IEEE C57.19.01, which specifically applies to transformer bushings, a category that includes many of the epoxy resin bushings we supply. For us, these standards aren’t just checkboxes—they’re the baseline for every design decision we make. When a customer orders an epoxy bushing for a 35kV transformer, we have to make sure the wall thickness of the epoxy, the type of resin blend, and the quality of the fiberglass reinforcement all match the thermal and electrical requirements laid out in these standards.
Beyond international standards, there are application-specific standards that apply depending on where the bushing is used. For low-voltage epoxy bushings, like those for panel-mounted switchgear, we follow different criteria than for high-voltage transformer bushings. Let’s talk about low-voltage first. LV epoxy bushings are used in everything from residential electrical panels to industrial control cabinets, where voltage is typically below 1,000V. The standards here focus more on mechanical durability, resistance to dust and moisture (LV areas can be just as prone to harsh conditions as high-voltage ones), and ease of installation. For example, panels in factories or outdoor installations need epoxy bushings that can handle vibration from heavy machinery and exposure to rain without cracking. Our panel-mounted LV epoxy bushings are tested to meet these specific requirements, so they’re reliable even in demanding commercial settings. You can learn more about these lower-voltage, panel-specific options here: Panel Mounted LV Epoxy Bushing
LV insulating epoxy bushings, the next category down, often go into smaller distribution transformers or power supplies, where the focus is on reliable insulation at lower voltage levels. The standards for these are a bit more lenient on dielectric strength than medium or high-voltage options, but stricter on compatibility with the conductors they hold. Because LV bushings are so widespread—there are millions in use across North America alone—standards also include requirements for traceability and consistent manufacturing. We track every batch of our LV epoxy bushings from raw resin to finished part, so customers can trust that every unit is identical to the last. To see how these LV insulation solutions are designed, visit: LV Insulating Epoxy Bushing
When we move up to medium and high-voltage epoxy bushings, like those for large power transformers, the standards get far more rigorous. A transformer bushing that fails can take the entire unit offline, leading to power outages that affect thousands of people, not to mention the cost of replacing the bushing and the transformer itself. The standards here include a range of critical tests: dielectric withstand testing, where we apply a voltage higher than the operating voltage of the bushing to make sure it doesn’t break down; thermal cycling tests, where we heat and cool the bushing repeatedly to mimic the temperature swings of operation; and mechanical load testing, where we apply force to simulate the weight of the conductor or the stress of installation. For our epoxy resin bushings made for transformers, these tests are non-negotiable. We don’t just test a sample from each production run—we test every design before it goes into full production, and we work closely with customers to adjust if their specific transformer has unique requirements. You can explore our epoxy bushings tailored exclusively for transformer applications here: Epoxy Bushing for Transformer
Another key set of standards that often gets overlooked is material-specific standards. Epoxy resin is the core material of our bushings, so the properties of that resin have to meet specific criteria. The American Society for Testing and Materials (ASTM) has standards for epoxy resins used in electrical applications, like ASTM D4066, which covers the properties of thermosetting molding materials, including dielectric strength, flexural strength, and heat resistance. For us, this means choosing epoxy blends that not only meet these material standards but also work well with the casting process. Poorly formulated epoxy can have voids or air bubbles during casting, which weaken the bushing and make it more prone to electrical breakdown. Our manufacturing team works to minimize these voids through precise mixing and casting processes, ensuring every epoxy resin bushing we make is dense, uniform, and meets all material requirements. That commitment to material quality is why so many long-term customers come back to us for their epoxy bushing needs—they know our parts don’t cut corners on materials.
Safety standards are another layer of this, especially for epoxy bushings used in public-facing equipment. Bushing fires or electrical arcing are rare when standards are followed, but they do happen when parts are subpar. Standards like OSHA (Occupational Safety and Health Administration) in the U.S. set requirements for components used in equipment that workers might access, dictating that epoxy bushings have a certain degree of flame resistance, for example. Our epoxy bushings are formulated to meet UL 94 V-0, the highest flame resistance rating for plastics, which means they stop burning almost immediately if exposed to a small flame. That’s a standard we prioritize because safety isn’t just a box to check—it’s part of our responsibility as a supplier.
Let’s talk about how these standards play out in real-world scenarios, because that’s where their value becomes clear. A few years back, we had a customer who was replacing porcelain bushings in a fleet of medium-voltage transformers. Porcelain was failing often due to cracking from impact—common in outdoor settings where transformers might get hit by debris or even small wildlife. They switched to our epoxy resin cast bushings, and we worked with them to make sure the parts met IEC 60137 standards for their specific voltage level. Not only did the epoxy bushings last 3 times longer than the porcelain ones, but they also passed all the required dielectric and thermal tests during field testing. That’s the payoff of adhering to these standards: parts that perform better, last longer, and reduce total cost of ownership for customers.
Of course, standards also evolve as technology changes. As grid infrastructure gets smarter, with more renewable energy and distributed power, the requirements for epoxy bushings are shifting. New standards are being developed to address things like partial discharge (small electrical leaks in the epoxy that can cause long-term damage) and compatibility with smart grid monitoring systems. As a supplier, we stay up to date on these changes—we invest in R&D, work closely with industry groups, and update our manufacturing processes to align with new standards. That way, our customers don’t have to worry about buying parts that will become outdated or fail to meet future requirements.
Now, I want to be clear: standards aren’t a one-size-fits-all solution. While global standards set the baseline, different regions or applications might have additional requirements. For example, a bushing used in a power plant in a coastal area needs extra resistance to salt corrosion, so we might add a UV-stabilized topcoat to our epoxy bushings to meet that specific environmental standard. As a supplier, we partner with our customers to understand their unique needs, then tailor our epoxy bushings to meet both the core standards and those additional requirements. That’s why we offer such a broad range of epoxy bushings—from low-voltage panel units to high-voltage transformer components—all aligned with the standards that matter for their application.
If you’re a working professional who needs epoxy bushings, or someone who just wants to understand what goes into making a reliable component, the key takeaway is this: standards are non-negotiable. They’re not just a set of rules from a distant boardroom—they’re the result of decades of experience, testing, and learning from what works (and what doesn’t) in the field. As a supplier, every epoxy bushing we ship is built to meet those standards, because that’s how we earn our customers’ trust.
Whether you’re procuring epoxy bushings for a new transformer, upgrading an electrical panel, or replacing a worn component, we’re here to help. Our team has years of experience navigating these standards, so we can guide you to the right epoxy bushing for your needs, test it to ensure it meets all requirements, and support you every step of the way. To learn more about our product lines or to start a conversation about your specific project, reach out to our team for procurement and technical support.
References:
- International Electrotechnical Commission. (2020). IEC 60137: Insulated bushings for alternating-current systems above 1 000 V. Geneva, Switzerland: Author.
- Institute of Electrical and Electronics Engineers. (2018). IEEE C57.19.01: Standard for performance, specification, and dimensioning of bushings for transformers. New York, NY: Author.
- American Society for Testing and Materials. (2021). ASTM D4066: Standard specification for thermosetting molding materials. West Conshohocken, PA: Author.
- Underwriters Laboratories. (2019). UL 94: Standard for safety of flammability of plastic materials for parts in devices and appliances. Northbrook, IL: Author.
