This is any length of flexible, multi-conductor cord having a male "attachment plug" at one end for plugging into a receptacle, and one or more female cord connectors at the other end. (UL 817). The Uniform Fire Code (UFC) further defines an extension cord as having no built-in over-current protection (UFC: Article 85).
It is important to distinguish between "extension cord sets" and "power cord sets" which are furnished as part of an appliance or tool for plugging into a receptacle or an extension cord.
UL does not permit more than 3 plug-in outlets on an extension cord unless the cord set is a minimum of #12 AWG (wire size) and type SJ or better cord. Cords for outdoor use are not permitted to have more than 3 outlets regardless of wire size (UL 817).
This device is not classified as a cord set or extension cord, but is referred to as a Temporary Power Tap (TPT). It is permitted to have six outlets because its over-current protection will protect the #14 AWG cord at its rated value of 15 amps. A TPT is intended only for indoor use as an extension of the branch circuit. (UL 1363)
Temporary Power Taps are often supplied with supplemental over-current protection, which is not the equal of a listed circuit breaker for reliability or effectiveness. Switches, indicator lights, a transient voltage surge suppressor (TVSS) and/or an electromagnetic interference (EMI) filter may also be included.
The word "temporary" is broadly interpreted because of the special need for the extra outlets where we have a cluster of appliances such as a computer, printer or disc drive. Admittedly this assembly may be used for months or even years without moving, but its length is limited to a maximum of 25 feet. UL (policy) considers this usage to be within the intent of the cord because such equipment is moved occasionally, and because there is no other practical way to provide for this very common need.
The main difference between temporary power taps and extension cords lies in the intended use of the products. UL lists extension cords as cord sets under the category of Cord Sets and Power Supply Cords. A cord set can have a current rating less than the branch circuit rating (depending on the ampacity of the cord and the rating of the devices such as cord-connector body or switch, whichever is less). For this reason, a cord set must be selected in relation to the rating of the equipment with which it is used. Cord sets extend the appliance power supply cord so that the appliance can be ".... energized from a receptacle outlet" [Section 400-7 (b)]. Temporary power taps extend the branch circuit.
This information was originally published in “Straight Talk on Extension Cords, Power Strips and Daisy-Chaining” by Ernie Harper, CSP.