technical article from Blue Sea Systems
Underwriters Laboratories Inc. (UL) is an independent, not-for-profit product safety testing and certification organization. The government classifies UL as a Nationally Recognized Testing Laboratory (NRTL). Although UL performs a number of functions, the two most useful to members of the marine industry are:
1. Standards creation and maintenance
2. Product testing and certification
There are other organizations that perform these functions. For instance, the Society of Automotive Engineers (SAE) creates SAE Standards, which are similar to UL Standards. Also, there are other NRTL's that can test and certify products.
UL is unique because:
1. Only UL can authorize the use of the well-known symbol, the circle with a UL inside.
2. UL is one of the oldest testing and certification organizations
3. UL is both a Standards creating and a product testing organization.
4. UL is a brand name, strongly associated with safety in the consumer's mind.
A common confusion about UL revolves around three terms:
1. UL Listed
2. Tested to UL Standard XXXX
3. UL Recognized
This designation indicates that the device has been tested by UL to a UL Standard and 'listed' with UL so that the UL circle logo can be applied to the product and claim conformance to the Standard. A UL Listed product can be installed in the field without further UL testing and be assured of having the performance characteristics under which it was tested and Listed by UL. Part of the Listing process involves UL making periodic inspections of the product's production to assure that it is being manufactured to the same specifications as the original test sample.
Tested to UL Standard XXXX
This designation indicates that someone used a UL Standard as the testing criteria for a product. Note that "Tested to UL Standard" does not necessarily mean that:
1. The product passed the test
2. A reputable organization conducted the test
3. The product will continue to be made as well as the one that was tested
In fairness, it should be noted that a product tested to a UL Standard by a NRTL and manufactured by a reputable company may be superior to a product that is UL Listed to the same standard. One reason for this can be that the manufacturer can more easily modify and improve non-Listed products since they are not subject to the constraints of the Listing process.
A device that is UL Recognized differs from a device that is UL Listed. A "Recognized" device is expected to be installed within a larger assembly by a manufacturer, not in the field, and this larger assembly is then expected to be tested by UL. The UL Recognition then allows UL to abbreviate the testing of the specific embedded Recognized component. UL Recognition has little value for end users installing devices in the field.
Original article from Blue Sea Systems