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As my March 2007 column “At the Service Entrance” detailed, inspectors, manufacturers, contractors and electricians have long debated the installation orientation of panelboards and circuit breakers. Should a panelboard be installed in only a vertical position, or can it be installed horizontally? Last month’s column titled “Panelboard Orientation” discussed this issue, but these next questions are the most controversial and debated. Can the panelboard be installed on its back, or would that be a violation of the National Electrical Code (NEC)? Does the positioning of the panelboard affect the workspace requirements of Section 110.26 for the panelboard?
These questions require the manufacturer of an assembly, the electrician/installer and the electrical inspector to determine if there is a legitimate reason to install a panelboard on its back. From the manufacturer’s point of view, incorporating a panelboard into a larger piece of equipment provides a single point of power in the form of a feeder into the equipment and multiple branch circuits distributed within the equipment.
Having a panelboard with multiple branch circuit breakers built into the equipment permits individual branch circuits to supply power to individual appliances or loads and permits a service technician to disconnect the power to each appliance without shutting off the entire commercial appliance center or custom-built food service center.
Commercial appliance outlet centers consist of one or more electrical outlets and may have one or more outlets of another type (gas, steam, water supply and drain) supported within a suitable enclosure. The enclosure itself may consist of individual components providing some compartmentalization, and a single cover may enclose all compartments. These units are intended for permanent indoor installation where more than one appliance may be used simultaneously. Custom-built food service equipment covers custom-built commercial food serving and/or cooking equipment and includes various combinations of electric broilers, heated food warmers, plate warmers, shelves, displays, servers, fryers, griddles, ranges, ovens, convenience receptacles and similar heated appliances. These units may also include refrigerated beverage cooler/dispensers, drinking water coolers, freezers, ice and ice cream makers, refrigerators, soda fountains and similar units.
There are usually two different mounting locations for panelboards in these units, either installed in the vertical position behind an access door or mounted on its back behind an access door. Obviously, there isn’t a problem with the first mounting position, assuming the vertical panelboard is located very close to the access panel and pointed out toward the opening to ensure there isn’t a clearance problem. Where the panelboard is located on its back in the top of the unit, the access door must permit ready access to the panelboard and the circuit breakers.
One of the first issues with this installation would be compliance with Section 110.26(A), since these panel-boards are likely to require examination, adjustment, servicing or maintenance while energized. The purpose of the clearance requirements is to provide enough space for personnel to perform any of the operations just mentioned without jeopardizing worker safety. Working space for equipment operating at 600 volts, nominal or less to ground shall comply with the dimensions of 110.26(A)(1), (A)(2) and (A)(3).
There are three conditions in Table 110.26(A)(1) covering working spaces. Condition 1 is where exposed live parts are on one side of the working space, and there are no live or grounded parts on the other side of the working space, or where there are exposed live parts on both sides of the working space that are effectively guarded by insulating materials. Condition 2 is where exposed live parts are on one side of the working space, and grounded parts are on the other side of the working space. Concrete, brick or tile walls are considered grounded since these materials are conductive. Condition 3 is where exposed live parts are on both sides of the working space. Table 110.26(A)(1) dimensions are applied as step-back distances away from the exposed live parts or from the enclosure front if the live parts are enclosed. Where a panel is mounted in a face-up position in the top of the equipment at a height not greater than 5 feet, there is plenty of distance to step back. However, where the unit is manufactured of stainless steel, a service person may have direct contact to legs and lower torso while working on energized parts.
Section 240.33 provides requirements for the mounting positions of panelboard cabinets. It states that enclosures for overcurrent devices shall be mounted in a vertical position unless that is shown to be impracticable. If it is impracticable to mount the panel in a vertical position, the question remains whether the panel could then be mounted face up or if that would be a violation? Panel 10 may have to provide the answer to this question for the 2011 NEC. Until then, consult the manufacturer and inspector. EC
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 [email protected].