Roofing and electrical conduit

1 T e c h T o d ay Roofing and electrical conduit The electrical code provides some guidelines regarding conduit placement by Mark S. Graham During roof system removal operations initial raceway or cabling and Roofing instal- shall be run perpendicular to the roof pen- or when mechanically attaching rigid board lation and may be penetrated by the screws etration point to supports a minimum of 25. insulation or membranes, Roofing profession- or other mechanical devices designed to pro- cm. (10 in.) below roof decking. als sometimes find electrical conduit embed- vide hold down' strength of the waterproof- Informational Note: the 25 cm (10 in.). ded within roof systems or placed directly ing membrane or roof insulating material.

2 Requirement is to prevent accidental damage below roof decks. In many instances, the Exception: Rigid metal conduit and inter- from saws used by fire fighters for roof venti- presence of electrical conduit is unforeseen, mediate metal conduit shall not be required to lation during structural fire.. problematic and potentially dangerous. comply with (E). This statement indicates NEC acknowl- However, the electrical code provides some Generally, wiring placed in metallic con- edges the potential for accidentally cutting guidance regarding electrical cables, raceways duit is considered protected by the electri- metallic conduit ; however, it does not ad- and boxes placed in or under roof decks.

3 Cal profession and appropriate for use in equately restrict metallic conduit placement most concealed spaces and areas subject or prevent such accidental cutting during electrical code to physical abuse. However, Roofing reroofing. NFPA 70: National electrical industry experience has shown Code (NEC) serves as the elec- fasteners used for mechanically NRCA's recommendations trical code for most jurisdic- attaching rigid board insula- electrical conduit embedded within roof sys- tions in the tion or membranes can tems or placed directly below roof decks can In NEC's 2011 edit- readily penetrate metal- be problematic for Roofing professionals. ion, Chapter 3-Wiring lic conduit embedded Although the electrical code provides some Methods and Materi- within or directly guidance regarding metallic conduit place- als provides place- underneath roof ment within or directly underneath roof ment and methods assemblies.

4 By way systems, experience has shown these require- for wiring. Sec- of comparison, ments are not adequate to address Roofing tion the wall thick- industry concerns. Protection Against ness of 1/2-inch- NRCA does not recommend metallic Physical Damage includes the following state- thick metallic conduit is comparable to the conduit or wiring be embedded within roof ment specific to wiring installed in or under metal thickness of a 20-gauge steel roof assemblies or placed directly below roof roof decks: (E) Cables, Raceways, or Boxes deck. Self-cutting or self-drilling roof fasten- decks. If metallic conduit or wiring needs Installed in or Under Roof Decking. A ers can readily penetrate metals of these to be placed near the roof assembly, NRCA.

5 Cable, raceway, or box, installed in exposed or thicknesses. recommends it be positioned and supported concealed locations under metal-corrugated Also, cutting and roof system removal at least 1 inches from the bottom side of sheet roof decking, shall be installed and sup- operations can damage and penetrate metal- the roof deck or substrate to which the roof ported so there is not less than 38 mm (11/2 lic conduit . Another section of the NEC, system is applied. Also, hangers or other in.) measured from the lowest surface of the Section Permitted, addresses supports used to attach and support metallic roof decking to the top of the cable, raceway, wiring methods for solar photovoltaic sys- conduit and wiring should be attached to or box.

6 A cable raceway, or box shall not be tems: (1) Beneath Roofs. Wiring methods framing or roof deck supports, not the roof installed in concealed locations in metal- shall not be installed within 25 cm (10 in.) deck or roof substrate. 123. corrugated, sheet decking-type roof. of roof decking or sheathing except where Informational Note: Roof decking mate- directly below the roof surface covered by PV Mark S. Graham is NRCA's associate rial is often repaired or replaced after the modules and associated equipment. Circuits executive director of technical services. 12 OCTOBER 2011.