The UL label in the USA and the CUL label in Canada on electrical products indicate that the products have been designed, built and tested to be in accordance with safety standards for those respective countries by Underwriter Laboratories. 

The CUL mark applies to products intended for the Canadian market that have been tested and found to comply with the requirements of CAN/CSA 22.1-12, which is the Canadian Electrical Code issued by the Canadian Standards Association. Included in this code under section 22.2 are two sections, numbers 236-M90 and 117 that deal with heating and cooling equipment and special purpose air conditioners. If a product is NOT CUL or CSA listed; it means that the product is not certified for use in Canada.

Their initials UL represent their mark of approval on all equipment that is specifically applicable to products designed and sold within the US, suitable for US electrical environment

  

1. Look for the UL/CUL trademark! It will always look like the picture above. Note that the UL is always in a circle, the U slightly above the L.
   
2. Right under the UL trademark, the word LISTED or CLASSIFIED will appear in all capital letters.
   
3. Under LISTED/CLASSIFIED you will find what the product is. In the case of the graphic above, the UL certificate would be for a “Class 2 Power Supply.”
   
4. Most importantly, under the product identity is the control or issue number. The control number is typically four alpha-numeric characters. The issue number is a sequence of 4 to 6 numbers, and is sometimes preceded by two letters or the phrase “Issue No.”
   
5. Other markings you may find with the Listing Mark are the UL file number; company name or logo; model, catalog or type designation; or electrical ratings.