A Serious Decision

Occasionally, a change occurs in the National Electrical Code (NEC), and the ramifications are not realized until after the Code is issued. One such change can be found in Section 210.4(B) in the 2008 NEC. On the surface, the change does not seem to seriously affect electrical installations, and only after an in-depth analysis does the real extent of the change surface. Incorrectly applying the new text could be a costly decision, so take care to understand the text completely as provided in the 2005 NEC and the new text as revised in the 2008 NEC.

To fully understand, one first must understand the definitions involved. A multiwire branch circuit is a “branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.” An individual branch circuit is a “branch circuit that supplies only one utilization equipment.” However, an individual branch circuit can be a multiwire branch circuit, as long as it consists of at least two ungrounded conductors with different voltage and sharing a grounded or neutral conductor. In addition, an individual branch circuit also can be a single circuit composed of an ungrounded conductor and a grounded conductor, or multiple ungrounded conductors without a grounded or neutral conductor.

In the 2005 NEC, Section 210.4(B) applied only to installations where a multi-wire branch circuit supplied more than one device or equipment on the same yoke, such as a duplex receptacle with the “hot” side jumper removed and “hot” conductors from different phases connected to each receptacle. If the neutral conductor was connected to the neutral side of the receptacle and it was common to both receptacles on the yoke, a disconnecting means was required to simultaneously disconnect all the ungrounded conductors. Either a common trip circuit breaker could be used or individual single-pole circuit breakers could be tied together using an identified handle tie. The purpose of this section was to ensure both ungrounded conductors supplying the two devices on the single yoke would be disconnected.

The change in Section 210.4(B) for the 2008 NEC has expanded the requirement for each multiwire branch circuit to be provided with a means to simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates. This text no longer applies only to two devices on a single yoke; it applies to all multiwire branch circuits supplying any load. For example, prior to the 2008 NEC change, a multiwire branch circuit could supply the overhead lighting system with three single-pole circuit breakers. Handle ties would not have been required. With the change in 210.4(B), these breakers must be disconnected simultaneously. Since circuit breaker handle ties are not designed for connection to three single-pole circuit breakers (only two), a three-pole internal trip circuit breaker must be used.

The change in 210.4(B) also appears to be in conflict with the text in 240.15(B)(1). The text in Section 240.15(B)(1) is as follows: “Except where limited by 210.4(B), individual single-pole circuit breakers, with or without identified handle ties, shall be permitted as the protection for each ungrounded conductor of multiwire branch circuits that serve only single-phase line-to-neutral loads.” Since all multiwire branch circuits now must be simultaneously disconnected, the permission in 240.15(B)(1) to use single-pole circuit breakers without handle ties for a multiwire branch circuit is not permitted.

Section 210.4(B) also creates another possible conflict in Section 410.130(G)(1). Section 410.130(G)(1) requires the installation of a disconnecting means (either internal or external to the luminaire) for each fluorescent (electric-discharge lighting system of 1,000 volts or less) luminaire that uses double-ended lamps and contains a ballast that can be serviced in place. Based on 210.4(B), the circuit breakers for the multiwire branch circuit must be tied together with a handle tie for two breakers or an internal trip for three-pole breakers. Disconnecting power to the lighting circuits in the office or store now means all lighting is off.

In addition, Section 410.130(G)(2) states, “When connected to multiwire branch circuits, the disconnecting means for the individual luminaire shall simultaneously break all the supply conductors to the ballast, including the grounded conductor.”

If the multiwire branch circuit breakers were used as the disconnecting means, this would be a violation because these breakers would not disconnect the neutral. Therefore, article 210.4(B) requires that the circuit breakers be tied together. Article 410.130(G)(2) also requires an additional disconnecting means for each individual luminaire, so all conductors to the ballast can be opened.

ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 or at mark.c.ode@us.ul.com.


About the Author

Mark C. Ode

Fire/Life Safety Columnist and Code Contributor
Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and Mark.C.Ode@ul.com .

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