Understanding Snap Switch Installation Requirements

Switching devices are often installed without reading installation instructions or without understanding certain concepts involved in the safe installation of these devices. A careful analysis of changes in the 1999 National Electrical Code (NEC) plus information in other standards will provide the installer with a better understanding of the requirements relating to switches. Article 380 in the NEC covers the installation and construction requirements for all switches, switching devices, and circuit breakers that are used as switches. Even though Article 380 is a very short article, the provisions in this article cover many different types of switches. There are dead-front switches, clock-operated switches, bypass isolation switches, general-use switches, general-use snap switches, knife switches, door switches, transfer switches, motor-circuit switches, and a multitude of other switches, all of which ultimately are covered by Article 380. Article 100 of the NEC defines many of these switches so that the NEC user can differentiate between the various types of switches without referring to other documents. For example, a general-use switch is intended for use in general distribution and branch circuits. The switch is rated in amperes and is capable of interrupting its rated current at its rated voltage. In other words, a 15-ampere, 125-volt switch must be able to open or interrupt the 15-ampere current across its contacts at the 120-volt operating voltage of the circuit. A general-use switch is constructed so that it can be installed in device boxes or mounted on covers, or used in conjunction with the wiring systems recognized by the Code. A general special-use snap switch (one that complies with UL 1054) is a specific general-use switch intended for an application in an appliance. It is not constructed to meet the requirements of Code installations. General-use snap switches can be installed in a group or ganged in boxes or enclosures, but the voltage between adjacent switches must not exceed 300 volts. A barrier can be installed between the adjacent switches if the potential on these adjacent switches exceeds 300 volts. An example of this would be two switches in the same box immediately adjacent to each other and fed from two separate phases on a 277/480-volt, three-phase system. In this case, the two switches would have a 480-volt difference of potential between them, necessitating either a barrier or a separate box. Occasionally, an installer may have a 277-volt lighting circuit and a 120-volt fan circuit in an installation, such as a commercial bathroom. The installer may want to provide a single switch to accomplish the simultaneous switching of the two separate circuits. Depending upon the two systems, the voltage could exceed the 300-volt maximum allowed by Section 380-8(b) and could constitute the same danger as may exist where the two circuits were installed on adjacent switches. However, the less obvious violation in this installation may be a violation of the listing on the switch. Multipole general-use snap switches have not been investigated for a connection to more than one circuit, unless the switch is marked for “two circuits” or “three circuits.” A change in Section 380-9 in the 1999 NEC should be reviewed concerning the grounding of the faceplates installed on many snap switches. This change requires all general-use snap switches of all types, including dimmer switches, to be effectively grounded. There are two options to accomplish the grounding of the switches. The first option is to connect the switches to an equipment bonding jumper and thus to an equipment grounding conductor that is a part of the circuit. The second option is to mount the switch to a grounded metal box with metal screws or to a nonmetallic box with integral means for grounding the switchdevices installed in the plastic box. Relying upon the screws for connection of the metal yoke of a switch to the box on which it is mounted without requiring a bonding jumper is different than the situation involving a receptacle. The screws attaching a regular receptacle (one that is not self-grounding) are not acceptable as a grounding means, since the receptacle will have more potential movement during its intended operation than will a switch. Snap switches must provide a means for grounding metal faceplates, whether or not a metal faceplate is installed at the initial installation. The grounding of the switch provides assurance that a metal faceplate will not become energized without an appropriate path to ground for any fault current. An exception to this requirement has been provided for replacement of existing switches. A switch that is being installed as a replacement for an existing switch is not required to be grounded where a grounding means does not exist within the snap switch enclosure, or where the wiring method does not include or provide an equipment ground. A snap switch that is permitted to be ungrounded according to this exception and located within reach of conducting floors or surfaces must be provided with a faceplate of a non-conducting and noncombustible material. Keeping these few requirements in mind while installing snap switches will make it easier to be in compliance with the NEC. ODE is staff engineering associate at Underwriters Laboratories, Inc., in Research Triangle Park, N.C. He can be reached at (919) 549-1726 or by e-mail at mark.c.ode@us.ul.com.

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