IAEI Southern Nevada Chapter

In the 2011 NEC, there is a new Informative Annex I, “Recommended Tightening Torque Tables from UL Standard 486A-B.” UL Standard 486A-B is titled “Wire Connectors” and is used to list connectors for aluminum, copper and copper-clad aluminum conductors. There are two columns (“A” and “B”) in each of the tables in Annex I. When used for listing connectors, Column A values are used for current-cycling tests, and Column B values are used for all other tests. When used for field connections, the values in Column B are the appropriate torque values to use. Although manufacturers can and do specify differing torque values (with appropriate testing) for connections, the standard values in Column B are commonly used. These values correspond to those published by major connector manufacturers such as Burndy, ILSCO and others.

Annex I states that “In the absence of connector or equipment manufacturer’s recommended torque values, Table I.1, Table I.2, and Table I.3 may be used to correctly tighten screw-type connections for power and lighting circuits.*” The asterisk directs the reader to the statement “For proper termination of conductors, it is very important that field connections be properly tightened. In the absence of manufacturer’s instructions on the equipment, the torque values given in these tables are recommended. Because it is normal for some relaxation to occur in service, checking torque values sometime after installation is not a reliable means of determining the values of torque applied at installation.”

Updated 5/27/2011

Transformers that are located too close to a residential service may let through too much current in the event of a fault. Residential service equipment is usually limited to 22k, but even that is superseded by the limitation of a 10k main. In order to verify that the available fault current is low enough to be safely interrupted by the overcurrent protective device, calculations must be performed. To calculate the available fault current at the service equipment, the following information is necessary: available fault current at the transformer and the size and length of the conductors. Placing the transformer farther away from the service equipment will decrease the available fault current due to the impedance of the wire connecting the equipment.

Updated 11/25/09

Manufactured wiring systems and pre-wired systems are not the same thing. Manufactured wiring systems are covered under Article 604, but pre-wired systems are covered under the entire NEC, not a specific article. Some pre-wired systems are listed by NRTLs. Pre-wired systems must comply with the requirements in the NEC including conductors sizing, grounding, etc. A pre-wired system is also know as a prefabricated wiring system, and UL lists them under category QQYZ "Wiring Assemblies."

Updated 11/25/09