How Much Working Space Is Enough?

Jan 1, 2009 12:00 PM, By Mike Holt, NEC Consultant

Exception: The minimum headroom requirement doesn't apply to service equipment or panelboards rated 200A or less in an existing dwelling unit. See the definition of “Dwelling Unit” in Art. 100.

Equipment such as raceways, cables, wireways, cabinets, and panels can be above or below electrical equipment, but must not extend more than 6 in. into the equipment working space [110.26(A)(3)] (Fig. 2).

Clear spaces

Working space covered by 110.26 must be clear at all times [110.26(B)]. Therefore, it can't double as a storage area. It's dangerous to service energized parts in the first place. It's unacceptable to subject electrical workers to the additional dangers of working around boxes, cabinets, and other impediments in their working space.

When normally enclosed live parts are exposed for inspection or servicing in a passageway, the working space must be suitably guarded from occupants using the passageway. Make allowances for a fire alarm evacuation, which will have numerous occupants moving through the passageway.

Entrance and egress

At least one entrance/egress of sufficient area must provide access to and egress from the working space [110.26(C)(1)]. Building codes contain minimum dimensions for doors and openings for personnel travel. Check with the AHJ for clarification of “sufficient area.”

You must have an entrance to and egress from the working space at each end of the working space of electrical equipment rated 1,200A or more, if the equipment is over 6 ft wide [110.26(C)(2)]. The openings must be not less than 24 in. wide and 6½ ft high. You can have a single entrance/egress, if:

The location permits a continuous and unobstructed way of egress travel, or
The required working space depth is doubled, and the equipment is located so the edge of the entrance is no closer than the required working space distance.

Fig. 4. Guidelines on installing foreign systems.

Where equipment with overcurrent or switching devices rated 1,200A or more is installed, personnel door(s) for entrance to and egress from the working space located less than 25 ft from the nearest edge of the working space must have the door(s) open in the direction of egress and be equipped with panic hardware or other devices that open under simple pressure [110.26(C)(3)]. This applies only to doors that are intended to provide an entrance or exit from the equipment room, so it doesn't apply to unrelated doors that are within 25 ft, such as a door leading to a janitor's closet. In addition, notice that while the requirement for two entrances/exits is dependent on the amperage and the physical size of the equipment, this rule applies regardless of the physical width.

Electricians who suffer burns on their hands in electrical arc flash or arc blast events often can't open doors equipped with knobs that must be turned, and they can't pull a door that opens toward them. Because this requirement is in the NEC, the electrical contractor is responsible for ensuring that panic hardware is installed where required. Some electrical contractors chafe at being held liable for nonelectrical responsibilities, but this rule exists to save the lives of electricians.

Illumination

Service equipment, switchboards, panelboards, and MCCs located indoors must have illumination in (or next to) the working space [110.26(D)]. Illumination must not be controlled by automatic means only.

The NEC doesn't provide the minimum footcandles required for proper illumination, but lighting application guides do. Proper illumination of electrical equipment rooms is essential for the safety of those working on such equipment.

Saving a few bucks on installed lighting only to incur the costs of temporary lighting or extended downtime later isn't good economics, but this isn't just a matter of economics. The safety issue makes good lighting not only sensible, but also imperative.

Dedicated space

Switchboards, panelboards, and MCCs must have dedicated equipment space and be protected from damage [110.26(F)].

Outdoor equipment must comply with 110.26(F)(2). For indoor equipment, the following requirements apply:

The footprint space (width and depth of the equipment) extending from the floor to a height of 6 ft above the equipment, or to the structural ceiling (whichever is lower), must be dedicated for the electrical installation. You cannot install any piping, ducts, or other equipment foreign to the electrical installation in this dedicated footprint space (Fig. 3).
Exception: Suspended ceilings with removable panels can be within the dedicated footprint space [110.26(F)(1)(d)].