NFPA Journal

BY DEREK VIGSTOL

The 2020 NFPA 70®, National Electrical Code® (NEC), features a number of revisions designed to protect people from electrical hazards. One important change to the new edition addresses safety for people working on service equipment.

The “six disconnect rule” has been around for a long time—we’ve been permitted to use up to six switches or circuit breakers in a common enclosure as the service disconnect since before World War II. However, this created a scenario where the bus in an enclosure could not be de-energized without disconnecting the service from the utility.

This presented a massive hazard to workers when performing work on services, since they were the point in the system with the highest available fault current and potential arc-flash incident energy. This was also compounded by the addition of alternative power sources on the supply side of service disconnects, such as solar and wind power. Essentially, this created a state where workers were exposed to equipment that could not be put in an electrically safe work condition.

NFPA 70E®, Standard for Electrical Safety in the Workplace®, requires that equipment be placed into an electrically safe work condition if a worker could be exposed to a shock hazard, or if there is an increased chance of injury from an arc flash. There are some specific conditions that justify not placing equipment in a safe work condition, such as when it’s not feasible to de-energize or when de-energizing poses a greater hazard or increased risk. However, needing to disconnect from the utility or other power source is not a justification for energized work. That meant workers were often needlessly exposing themselves to this dangerous situation.

The solution: provide a way to turn the electricity off without involving the utility or altering any supply-side connections from other sources. That’s the focus of the new revision to section 230.71, which says that each service must only have a single means of disconnect.

Exceptions are almost always inevitable for these kinds of general rules, and this one is no different. For instance, occupancies like shopping centers, multi-family dwellings, and office buildings benefit from having multiple disconnecting means on a single service, a commonly used design feature in these instances. To address this, 230.71(B) was also revised to list a set of conditions where the design can utilize up to six disconnects. This is a very specific list of conditions that must exist in order to have multiple disconnects on a single service. Two to six disconnects are permitted, provided that they consist of a combination of any of the following: separate enclosures, each with a main service disconnect; panelboards with a main service disconnect; switchboard(s) with only one service disconnect in each separate vertical section with barriers separating sections; and switchgear or metering centers where each disconnect is in a separate compartment.

This means that a “main lug only” panelboard can no longer be fed from the service conductors with individual circuit breakers serving as the service disconnecting means—a major step forward in requiring safety by design when it comes to worker wellbeing.

Like other requirements in the NEC that consider worker safety, this change to the latest NEC will take some adjustment in system design and installation. However, when we fully understand that the driving force behind this change is preventing injuries to workers servicing our electrical equipment, we can see just how important this change is to the purpose of the NEC. 

—Derek Vigstol is an NFPA technical lead, Electrical Tech Services. NFPA members and AHJs can use the Technical Questions tab to post queries on NFPA 70 at nfpa.org/70next.