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I am planning to run a new circuit to install ceiling lights, fan, etc. My attic is very low (approx 3 feet), and there is insulation between the joists (B in picture), so it is going to be a hassle to drill a hole in each one to run the cable through and under the insulation. I have a roof joist (A in picture) that is under the peak of the roof. I would rather run the cable along that, but I'm not sure if there are any issues with doing this. Is this a good idea?

P.S. I am in Seattle, so almost no lightening storms.

P.P.S. This is not my roof, but it is very similar. Except it isn't insulated.

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  • This answer provides some alternatives. – Tester101 Jan 23 '15 at 19:46
  • Is there a permanent ladder or stairs to gain access to the attic? – Tester101 Jan 23 '15 at 19:47
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If there's no permanent ladder or stairs leading to the attic, you may be able to simply lay the cable across the rafters.

"Where this space is not accessible by permanent stairs or ladders, protection shall only be required within 1.8 m (6 ft) of the nearest edge of the scuttle hole or attic entrance.".

National Electrical Code

Chapter 3 Wiring Methods and Materials

334.23 In Accessible Attics. The installation of cable in accessible attics or roof spaces shall also comply with 320.23.

Article 320 Armored Cable: Type AC

320.23 In Accessible Attics. Type AC cables in accessible attics or roof spaces shall be installed as specified in 320.23(A) and (B).

(A) Where Run Across the Top of Floor Joists. Where run across the top of floor joists, or within 2.1 m (7 ft) of floor or floor joists across the face of rafters or studding, in attics and roof spaces that are accessible, the cable shall be protected by substantial guard strips that are at least as high as the cable. Where this space is not accessible by permanent stairs or ladders, protection shall only be required within 1.8 m (6 ft) of the nearest edge of the scuttle hole or attic entrance.

(B) Cable Installed Parallel to Framing Members. Where the cable is installed parallel to the sides of rafters, studs, or floor joists, neither guard strips nor running boards shall be required, and the installation shall also comply with 300.4(D).

Article 300.4(D) says that if you do attach the cable to the ridge beam, you'll have to keep it 1 1/4" away from either edge.

Article 300 Wiring Methods

300.4 Protection Against Physical Damage. Where subject to physical damage, conductors shall be protected.

(D) Cables and Raceways Parallel to Framing Members and Furring Strips. In both exposed and concealed locations, where a cable- or raceway-type wiring method is installed parallel to framing members, such as joists, rafters, or studs, or is installed parallel to furring strips, the cable or raceway shall be installed and supported so that the nearest outside surface of the cable or raceway is not less than 32 mm (1 1⁄4 in.) from the nearest edge of the framing member or furring strips where nails or screws are likely to penetrate. Where this distance cannot be maintained, the cable or raceway shall be protected from penetration by nails or screws by a steel plate, sleeve, or equivalent at least 1.6 mm (1⁄16 in.) thick.

  • Just laying the cable across the rafters feels odd. It's a tight enough space that I can easily see getting caught up in it while working up there. I think that the roof beam is a 2X10, so there is plenty of clearance. Thanks! – Erick T Jan 23 '15 at 20:47

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