Avoiding Explosion Hazards, Replacing Metal-Halides And More

By Jim Dollard | May 15, 2016




Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code (NEC), Jim will help you solve it. Questions can be sent to [email protected]. Answers are based on the 2014 NEC.

Battery locations

I recently read a paper on explosion risks in battery rooms that has me concerned. The project requires us to run a significant amount of conduit through the battery rooms. There is adequate space for our work, and we take multiple precautions to ensure that we do not come in contact with the battery system or create an arc-flash incident. One of my employees asked me if there is an explosion hazard due to an accumulation of gases in the room. The question came up because there were no gas sensors that we could see in the room. There are fans with dampers to vent air outside, but they do not run. Does the NEC require signage for this installation? Are gas sensors required? How can we determine that there is no explosion hazard?

The NEC requirements for ventilation of battery locations or “battery rooms” are located in Section 480.9(A). The NEC requires the battery installation to include provisions to ventilate where an accumulation of explosive gas is possible. These provisions must be based on and be appropriate for the battery technology applied in that location or room. These provisions can include constant air movement or a detection system that purges the location when necessary. An informational note informs the Code user that “some battery technologies do not require ventilation.” 

A designing engineer may apply multiple other standards with respect to the potential accumulation of explosive gases. The NEC contains no prescriptive signage requirements that would apply to ventilation in battery locations. It would be prudent to discuss the need for ventilation with the owner prior to performing work in these locations. There are many other potential safety concerns to consider. Article 480 also requires minimum working space, personnel doors that open in the direction of egress with listed panic hardware, and adequate illumination. Eyewash stations may also be required. See NFPA 70E for information on an arc-flash risk assessment.

conductor terminations

I installed multiple load centers from a major manufacturer sized at 125A last year. The neutral termination bars are already maxed out, and I am looking for additional neutral space. What part of the Code governs the installation of an additional neutral termination bar in my load center?

The NEC does not specifically address expanding a panelboard or load center’s capability to terminate grounded (neutral) conductors. Section 110.3(B) will require the listed load center or panelboard to be installed in accordance with any instructions in the listing or labeling. Manufacturers typically have many “identified” accessories that can be purchased and used in their load centers or panelboards. It is important to note that the general rule in Section 408.41 requires each grounded (neutral) conductor in a load center or panelboard to terminate in an individual terminal that is not also used for another conductor.

Expansion-fitting bonding jumpers

When installing expansion fittings in a run of EMT, are exposed bonding jumpers required? We have a potential issue with design drawings that note bonding at each expansion fitting on a bridge project. Does the NEC require the bonding to be visible after installation? How do we determine what size bonding jumper to use?

No, the NEC does not require bonding at expansion fittings to be visible. However, in some cases, such as larger conduits with parallel conductors, external bonding jumpers may be required to facilitate larger bonding jumpers. Section 250.98 provides requirements for bonding loosely jointed metal raceways. Expansion fittings (there are many types) and telescoping sections of metal raceways are required to be made electrically continuous by equipment-bonding jumpers or other means.

Manufacturers typically provide the required bonding inside the expansion fittings. This is preferred because it is part of a listed product and is not subject to physical damage that could exist if the bonding jumper were installed outside of the raceway. Manufacturers install bonding jumpers and other means internally to achieve the required electrical continuity. The type of conductors installed will determine the bonding jumpers’ size. Supply-side bonding jumpers must be sized according to 250.102(C). Load-side bonding jumpers must be sized according to 250.102(D). The installer must read the manufacturer’s instructions to determine if the correct size bonding jumper exists inside the expansion fitting for the type of conductors installed. In some cases, an external-bonding jumper may be required.

Metal-halide lamp replacement

We are renovating a warehouse that has not been in use for more than 15 years. The majority of existing lighting is open type, high-bay metal-halide-type fixtures, some of which we have energized for temporary lighting. When trying to order additional lighting fixtures, I was told we had to buy fixtures that will allow only “Type O” metal-halide lamps because it was an NEC requirement. We cannot find that and are curious as to why older style lamps in use in the facility are no longer permitted.

The NEC contains requirements for “metal halide lamp containment” in Section 410.130(F)(5). This is located in Part XII, Special Provisions for Electric-
Discharge Lighting Systems of 1000 Volts or Less, because of the voltage applied to a metal-halide lamp to strike an arc. Metal-halide luminaires, other than those with a thick-glass parabolic reflector, are required to have a containment barrier that encloses the lamp, or they must be provided with a physical means that only allows the use of a lamp that is Type O. The older style lamps do not provide a shroud around the arc tube to contain it in the event it ruptures. This is necessary to prevent a rupturing arc tube from showering molten metal over combustible material and starting a fire. 

There are also documented injuries that occurred where the outer shroud of older style lamps is compromised, resulting in serious burns from ultraviolet light. As noted in your question, these luminaires are being used for temporary lighting. It should be noted that Section 590.4(F) and OSHA 1926.405(A)(2)(ii)(E) require that all lamps be protected from accidental contact or breakage.

Grouping of service disconnects

During the renovation of a shipping facility, we upgraded the service equipment and installed five, 200-ampere fusible disconnects as permitted in Article 230. There was significant discussion about the location of the disconnects and if they were in fact “grouped” as required by the NEC. The service entered the electrical equipment room in the corner, so we mounted three switches on one wall and two on an adjacent wall. The electrical inspector informed us that, to be considered as “grouped,” all of the switches had to be on the same wall, since there was room to fit them. Each disconnect was 18 inches apart, and the distance between the closest switches on adjacent walls was 3 feet. After many emails with pictures and several phone calls to the municipality, the inspector finally agreed to approve the installation. Does the NEC explain what must be done for switches to be considered grouped?

No, the NEC does not provide a prescriptive description of what is meant by a “group of separate enclosures.” Section 230.71(A) permits up to six disconnects mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard or in switchgear.

It is important to understand the reasons behind this requirement. It is necessary to have the permitted disconnects in the same enclosure or grouped in the same location for installer/maintainers to quickly identify all potential utility sources. This would also allow an individual to quickly open all service conductors to the building or structure in the event of fire or other emergency. In my opinion, the distances you provided in your question clearly illustrate that the disconnects you installed are a “group of separate enclosures.”

The NEC relies heavily on the authority having jurisdiction to make these decisions on a case-by-case basis. It is not feasible or practical for the NEC to provide a maximum or minimum distance in all cases. This is similar to the requirement for the location of the service disconnect inside of a building or structure. Section 230.70(A) requires that the service disconnect be readily accessible nearest the point of entrance of the service conductors. No maximum length is provided because those conductors should terminate in the service disconnecting means with the least amount of service conductor length possible.

About The Author

DOLLARD is retired safety coordinator for IBEW Local 98 in Philadelphia. He is a past member of the NEC Correlating Committee, CMP-10, CMP-13, CMP-15, NFPA 90A/B and NFPA 855. Jim continues to serve on NFPA 70E and as a UL Electrical Council member. Reach him at [email protected].






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