Understanding Safety Standards for Standard and Custom Transformers & Magnetics
There is often confusion about safety standards and approvals such as UL5085 applied to components and equipment. Engineers often know they need parts that are UL approved but what that actually means is often not understood.
Products that meet UL requirements can be either “listed” or “recognized.” Listed products are generally an end product of some kind, appropriate for use as a standalone unit. Products such as a piece of electronic equipment or an instrument are generally “listed.”
Products that are “recognized” are appropriate for use as a component in a larger system. Transformers almost always fall into the “recognized” category because they are almost always installed as a component in a circuit or larger piece of equipment.
To make matters more confusing for the transformer customer, there are different types of safety approvals for transformers within the UL5085 standard. For example, UL5085-1 applies to all power transformers. UL5085-2 and UL5085-3 apply to ‘Class 2 Transformers’. Class 2 transformers are power transformers that have been designed and constructed with a higher level of safety features, e.g. short-circuit tolerance, added isolation, etc.
When designing a new system, engineers prefer to use recognized components if they are available. Using recognized components reduces the amount of safety agency (such as UL) testing that needs to be done on the finished system design. If recognized components are not used, the safety agency may decide to run a full set of component-level tests on the transformer as a standalone unit to ‘recognize’ it, and then evaluate its fitness for use in the overall system. Using recognized transformers allows the safety agency to skip the component level testing because it was already done (and paid for) by the transformer manufacturer.
There are a number of companies that act as safety agencies, the most well-known of which is Underwriter’s Laboratories, or UL. These companies maintain testing standards and perform testing on components to ensure they are safe for use in the intended application. This is what is meant by ‘recognized.’ They also perform follow up services to inspect factories and make sure that components continue to be manufactured to the same standards and with the same materials for which they were originally recognized.
When a safety agency tests and approves a product, it creates a ‘construction file’, which is a document that sets out the details of how a component or product needs to be constructed in order to meet the recognition requirements. Safety agencies and the companies that work with them have some flexibility in how the construction file is written. For example, some construction files may allow a company to substitute recognized transformers from different suppliers without issue. Other construction files may be written to require a company to use only one specific model number of one specific transformer forever and ever. If the company wants to change suppliers, it has to re-open the construction file and pay the agency to test alternate components.
CET Technology has been working with UL and other safety agencies for almost 30 years, and we have become very good at extracting the most testing value for the least investment. Call us today and let us help you navigate the confusing (and expensive!) world of safety agency approvals on your transformers.
