UL Subject 2745 – addressing safety challenges of meter socket adapters
More and more communication devices are being powered directly from an electric meter adapter to take advantage of the more reliable power supply and to facilitate communications needed for smart grid applications. The National Electrical Code was revised in 2011 (Article 230.82(9)) to permit certain types of listed (certified) communications equipment to be connected prior to the service disconnect, i.e. in a meter socket adapter. Along with this “permission” came the understanding that the listing of such devices would adequately address the safety issues associated with connecting equipment at the service entrance.
Subject 2745 is the basis for the requirements for certification in product category POBN – Meter Socket Adapters for Communications Equipment. The outline covers both wired and wireless communications devices, or power supplies powering such devices, installed in a meter socket adapter. Communications utilities, communications network providers, authorities having jurisdictions (AHJs) and building owners are particularly interested in the Subject 2745 requirements if they have network elements connected to or powered from meter socket adapters which are connected to essentially unprotected power lines.
In addition to compliance with UL414 - Meter Sockets, these products also need to provide and maintain the isolation from mains voltages under extreme electrical and environmental conditions as would be expected for the communications equipment connected to the service. Subject 2745 requires the equipment to withstand the electrical surge and fault environment of such an installation without compromising the isolation between the primary circuits and communications networks or increasing the risk of fire or explosion hazards.
For example, prior to the service disconnect, there is nothing to reduce the level of electrical surges on the power lines. Also, the available fault current can be extreme. In the event of a component failure, communications equipment in a typical building installation may be subjected to a fault current of 200 amperes or less. However, prior to the service disconnect, the fault current can be 5,000 – 10,000 amperes or more. These situations require a very different level of component selection and testing. Standard power supplies, instrument fuses and surge protectors commonly used for communications equipment are generally not suitable for devices used in the meter socket adaptor environment.
Subject 2745 helps manufacturers consider safety at the beginning of the product development phase. It highlights the design elements for consideration and familiarizes manufacturers of communications equipment or communications equipment power supplies with the electrical environment associated with equipment installed at the electrical service entrance prior to the main service disconnect.
It has been more than a year since UL published the first edition of Outline of Investigation (OOI) for Meter Socket Adapters for Communications Equipment (Subject 2745) in March 2011. In order to prepare for the transition of the Subject 2745 to an American National Standards Institute (ANSI) standard, UL is currently working with customers to complete several investigations to gain a better understanding of equipment design and use and the application of the requirements.
For more information, please contact Chris CH Lin, business development manager for batteries and power supplies.
