Hello,
UL (previously Underwriters Laboratories) is an American safety and consulting company that sets and administer various standards and certificates for electrical and electronic products, among other things. When it comes to non-metallic electrical enclosures, the relevant standards to look out for are:

• UL94 – Tests for Flammability of Plastic Materials for Parts in Devices and Appliances
• UL746C – Polymeric Materials-Use in Electrical Equipment Evaluations
• UL50 – Enclosures for Electrical Equipment, Non-Environmental Considerations
• UL50E – Enclosures for Electrical Equipment, Environmental Considerations
• UL508 – Industrial Control Equipment (comparable with IEC 60947-2 and IEC 60947-4-1)

UL standards are extremely stringent, placing the entire process (from source material through to manufacture and packaging) under the microscope. This not only makes the standards all but compulsory for OEMs hoping to tap into the American market, it also means that the standard is fast becoming recognised internationally.
Any enclosure that is UL approved will have a corresponding mark clearly visible on its casing. This may be a standard UL symbol; a variant such as the C-UL US (for Canada) or UL-EU (complies with corresponding EN standards); or the RU ‘recognised component mark’ which is placed on components which are intended to be part of a UL listed product but which cannot bear the full UL logo themselves.
If the product is bought from a reputable manufacturer, dealer or distributor and bears the UL mark then you can be confident that it’s legitimate. Of course, if you still have concerns you should call your supplier and ask them to give you details of the testing processes that the enclosures have been exposed to.
All Spelsberg enclosures are tested at our in-house test centre which is audited annually by UL and approved to award all relevant standards. This way we can be sure that not only is every enclosure manufactured to the highest standards, they are tested accurately and reliably to provide peace of mind to our customers.
For more information about UL compliance and testing download this pdf.
Read about our UL approved European test facility here.
If you’d like more specific information about the Spelsberg range of UL approved electrical enclosures, then please feel free to drop me a private message.