What does RU (UR) label on DC power relays mean?

Question

I'm trying to figure out what does RU or maybe UR label mean on the body of many many relays. It's labeled almost on all (I've seen so far) DC relays which make me very curious :). Any suggestions?

Answer 1

It is a UL label. From UL wikipedia article:

The "Recognized Component Mark" is a type of quality mark issued by Underwriters Laboratories. It is placed on components which are intended to be part of a UL listed product, but which cannot bear the full UL logo themselves.[6] The general public does not ordinarily come across it, as it is borne on components which make up finished products.

Answer 2

RU is an Underwriter's Laboratories mark for certified products that are intended to be used inside of other devices.

Reference: The UL site.

Answer 3

It is the Recognized Component Mark UL

As a basis for approval, code authorities look for UL Listing Marks to verify that products have been investigated for installation in the field in accordance with model codes. During inspections of electrical installations, code authorities may see a variety of certification marks, including the UL Listing Mark and UL Recognized Component Mark. To properly approve the installation, it is important for code authorities to understand the meaning of each of these marks as well as the important differences between them. The UL Listing Mark is the most common certification mark seen and accepted by code authorities.

http://ul.com/wp-content/uploads/2014/04/ul_RecognizedComponentMarks.pdf

Answer 4

UL listings are for products. ЯU is for components and it means the component is pre-approved.

Say you design a DVR or smart-switch. The DVR needs a UL listing to be sold at retail. The smart switch needs a UL listing to be installed in mains wiring (NEC 110.2). You send the unit into UL, and they go through the unit with a fine-tooth comb.

For instance there's a relay in there, they'll pop it off the PCB and do their tests - hi-pot, current, throw cycles, physical teardown, toxic-smoke test (if burned), etc. This costs you money.

However, when they see the ЯU mark on the relay, they don't test it. It's already tested and approved. When your PCB is covered with ЯU components, listing is cheaper, faster, and there's less uncertainty.

Note that you can get a UL product listing from ETL, CSA, BSI, TUV, or any other Nationally Recognized Testing Lab. But they'll just follow the same rules as UL. A few Chinese junkmakers in the smart-switch space are trying to "go legit", and I notice they prefer ETL.