Practical Engineering: Properly Specifying Electrical Insulation Systems

Introduction

When developing electrical and electronic products that utilize transformers and other isolation devices, ensuring proper insulation system ratings and approvals for safety is essential. Unfortunately, many people lack awareness of these requirements. Without proper training, verifying system suitability becomes challenging. This article briefly explores the correct use of UL iQ for Electrical Insulation Systems (Reference 1) and highlights how proper utilization can save time and money during product development.

Classes of Insulation

According to IEC 60085, insulating materials are categorized into different classes based on the maximum winding temperatures. These ratings are listed in Table 1 for normal operating conditions:

Table 1 

From experience, Class B and Class F are the most commonly used insulation classes. Class H systems, on the other hand, find application in extreme environments where exceptional reliability is essential. So, when someone refers to using a Class B insulation system, you now understand what they’re talking about.

What is the Issue?

You can’t simply combine wire rated at 180°C, varnish rated at 200°C, plastic rated at 130°C, and so on, and call the resulting system a 130°C system. True qualification occurs only when all the components making up the insulation system are tested together, resulting in a specific rating (such as Class B).

Qualifying an insulation system that includes components not already approved is time-consuming and expensive. It typically takes several months to ensure proper qualification. Delaying inspection of the insulation system until the end of the product development cycle can lead to third-party safety approval failure by an NRTL just when you’re ready to put the end product into production.

When developing a new product and designing a transformer (for instance, for a switch-mode power supply), it’s crucial to determine the required insulation class and verify that the chosen insulation system has the correct rating well in advance. This ensures a smooth process when taking the product to an NRTL test facility.

How to Determine Class of Insulation

Determining the insulation class depends on the expected temperature of the insulation when the transformer operates within the end product at the highest ambient air temperature. Let’s consider a scenario where we need to find a suitable Class B insulation system for our transformer.

UL iQ for Electrical Insulation Systems Database

Reference 1 is the location of UL iQ for Electrical Insulation Systems Database. The landing page is shown below:

Notice that at the top of the page, you can search by File Number, Company, System Designation, or Component Search.

File Number

If you select File Number, the website brings up a selector where you can look for an insulation system via the insulation system’s holder’s UL File Number. This page looks like this:

From here, the best thing to do is click on any of the File Numbers you think might have the insulation system you need and read more about them. Below, I selected the first File Number for E100483 SABIC INNOVATIVE PLASTICS US LLC to see what insulation systems they have available. The result is shown below:

Notice that this supplier has three Class B 130-degree insulation systems available and one Class H 180-degree system. Select any of the System Designations to review the details of these insulation systems.

Company

Searching for insulation systems via Company follows a similar approach to searching by File Number as described above.

System Designation

Searching via System Designation is more involved in knowing what System Designation you want to find ahead of time. So, if we wanted to find the Class H 180-degree LNP-OTF system from SABIC, we would type “LNP-OTF” in for System Designation. From here, details of the LNP-OTF system are shown.

Component Search

As shown below, Component Search has more fields used to find suitable insulation systems.

With the Component Search, it is possible to select from a dropdown menu in the System Class/Endurance tab, and it brings up a list of all approved insulation systems under that specific insulation class.

Pro Tip: After selecting an insulation system, it’s crucial to verify that the device (in this case, a transformer for use in a switch-mode power supply) is constructed using the exact components specified in the UL iQ for Electrical Insulation Systems database. Recently, I encountered a situation where the insulation system required the use of ABC-XYZ plastic. However, ABC-XYZ+ (with the plus) was mistakenly considered suitable (because it has a plus, it must be better, right?). Unfortunately, the plus material wasn’t superior to the non-plus material. These two materials were not interchangeable, and one wasn’t a subset of the other. This oversight caused unnecessary delays that could have been avoided if the correct materials had been verified earlier in the product development cycle.

Conclusion

This article briefly covered using UL iQ for Electrical Insulation Systems. For additional details and a historical perspective on how the qualification of insulation systems originated, refer to references 2 and 3.

References: Further Reading and Watching

1. UL iQ for Electrical Insulation Systems. Retrieved from UL iQ for Electrical Insulation Systems.
2. Electrical Insulation System Performance and Reliability, Mark Raymond UL. Retrieved from Electrical Insulation System Performance and Reliability, Mark Raymond UL.
3. UL 1446 Systems of Insulating Materials, Mark Raymond UL. Retrieved from UL 1446 Systems of Insulating Materials, Mark Raymond UL.