Power cabling and connectors are a vast subject, covering different levels of power transmission that can feel infinite in their variation. The connectors for these cables reflect this in the wide variety of styles and form factors that are in use today. With all this variation, along with the extreme risks associated with power, it is extremely important that we ensure the vessels used to transmit this power are as safe as they are reliable.
Narrowing our focus, cabling and connectors that only carry power up to 16A can be used to power a host of different equipment such as AC and DC motors, servos, and lighting fixtures. Because connections for these devices must be reliable and safe, third-party certifications are used on a regular basis to ensure that the cabling and connectors selected are up to the task.
In the United States, Underwriters Laboratories is the primary third-party organization trusted to certify that electrical products are safe for use. That applies not only to electrical characteristics, but also to the environmental protection the connection affords. You will find the UL mark of certification on electrical products across the spectrum. Manufacturers that wish to submit their products for certification so that they can be used in these types of applications will generally have three different UL specifications to reference.
UL 1977: Simple certification
UL 1977 is probably one of the more common test specifications used for electrical connectors. It allows testing products that could be rated to transmit 1,000A of current or 600V AC or DC. It does, however, require that the OEM purchasing the connector is also the installer. Assembly of the connection after it leaves the OEM voids the UL certification.
This specification also does not account for any environmental ratings for the connectors alone. To achieve UL certification with regards to environmental protection, the connector must be evaluated in its installed condition. That means an additional submission request to UL beyond that which an OEM would normally need to perform. Obviously, products need to be installed properly and checked for safety, but this can be achieved in a more efficient manner by using products approved under alternative test specifications.
UL 2238: Test environmental protection
UL 2238 is used mostly for data, signal, and control transmissions, but will also account for power as well with a 60A, 600V AC or DC limitation. Bear in mind, however, that because the standard wasn’t written with power as its focus, it does not specify the most stringent requirements.
On the other hand, this specification does account for many of the issues with UL 1977. The most significant is that it allows for the direct testing of environmental protection. While it sub-contracts out the work to UL 50E, a product can be listed with UL Environmental Type Ratings included, without an additional review of the connector in its final application.
Another advantage of UL 2238 over UL 1977 is that it allows for connector installation at the OEM or in the field. This makes it much easier for end users to install UL certified products from multiple OEMs. Another bonus is that the requirements under UL 2238 line the connector up for use in NFPA 70 (Article 725) environments. While UL testing and certifications focus mainly on electrical cabinets and individual components, NFPA looks more at the overall site for safety. Knowing that UL 2238 already defines testing that coincides with NFPA 70 makes the final installation that smoother.
UL 2237: Specify transmission safety
UL 2237 is, ultimately, the most comprehensive standard for power requirements. It has all the advantages of UL 2238, but goes a few steps further, as its test standards address power transmission safety more thoroughly.
For one, there is no current limit, and the voltage limit is 1,000V AC or DC. Second, UL 2337 requires a short-circuit current rating and must meet a 5kA minimum rating. This is optional under UL 2238, but most suppliers do not opt in for that additional testing. It also addresses not only the requirements for NFPA 70, but also NFPA 79 environments.
The most noticeable difference between UL 2237 and UL 2238 is in the final current rating that a connector can achieve. As an example, we can look at 7/8in form-factor cordsets and connectors. Most were initially certified under UL 2238, allowing for nearly 25A in some configurations. As those connectors are re-tested under UL 2237, suppliers are finding that 15A becomes the upper limit. This is going to prove troublesome for the future of 7/8in connectors. There is a new M12 form factor now available in the market that can achieve a 16A rating under UL 2237. Since M12 is about half the size of a 7/8in connector, it will be difficult to justify the extra space required by 7/8in for the privilege of running less power.
Understand your application
As you look for power connectors for different applications, remember that while UL certification is often required, not all certifications are equal. When addressing power needs, be sure to confirm that the product you choose includes UL 2237, so the installation will ultimately be as safe and easy to implement as possible.