Multi-Wire Branch Circuits

InsightsPicWireSpools.gifWhen the 2008 National Electrical Code (NEC) introduced 210.4(B) entitled "Disconnecting Means," this new requirement for multi-wire branch circuits drove many questions related to the application of handle ties in the industry. This requirement has also driven more use of field applied handle ties. The application of handle ties on two one-pole circuit breakers must be performed correctly as the lack of attention to details could cause you to apply the product outside of its rating. Two one-pole circuit breakers can be tied together with an approved handle tie but you must pay close attention to the markings and listing of the products to ensure that the breakers are not applied outside of their rating.

Shared Neutral Applications

The shared neutral application is familiar to many electrical contractors, especially in light of copper prices these days. Sharing the neutral on the home run circuit from the breaker to the first outlet can be one way of reducing material costs. Those applications where you would have pulled two two-conductor (+ ground) wires instead are pulled with a single three-conductor (+ ground) wire. Section 210.4 of the NEC addresses multi-wire branch circuits, noting that these circuits are those where all conductors originate from the same panelboard or similar distribution equipment.

An approved handle tie applied to two single-pole breakers for such applications as shared neutral installations ensures the installation meets the requirement of section 210.4(B), “Disconnecting Means,” of NEC 2011 which states:

(B) Disconnecting Means. Each multi-wire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.”

Section 210.4(B) does not require the breaker to disconnect all ungrounded conductors in the case of a trip. A breaker that operates such that only that pole which experienced the overcurrent trips, while the other doesn’t, is termed as an independent trip type of device. This section requires that when you turn the breaker to the off position, all poles are turned to the off position.

This is a safety requirement that ensures the first outlet box does not have energized conductors present. NEC 2008 introduced this new section as a result of Proposal 2-10 of the ROP document for NEC 2008. The submitter’s substantiation stated:

“Multi-wire branch circuits employing shared neutrals can offer unexpected shock hazards to electricians unless all ungrounded conductors from the multi-wire branch circuit are disconnected simultaneously. The safety concern associated with unintentional voltage being present on multi-wire branch circuits during maintenance is not always fully appreciated. An electrician may not know that a circuit is a multi-wire branch circuit when work begins. Even if aware of a multi-wire branch circuit, there is presently no requirement to identify and disconnect all ungrounded conductors of that multi-wire branch circuit. The present NEC correctly recognized this as a safety issue in 210.4(B) for the limited situation of ‘more than one device or component on the same yoke.’ While the use of multi-wire branch circuits is a valid use, it should be permitted only where a means is provided to disconnect simultaneously all ungrounded conductors of that circuit.”

Applying the Approved Handle Tie

InsightsPic_BreakrPnl.gifCare must be taken when applying an approved handle tie to two single-pole breakers in the field. As stated earlier, the practice of doing this was made easy due to the fact that most single-pole breakers you work with in residential systems are slash-rated. Sometimes the fact that most are slash rated can lead toward a violation due to not reading the lab