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31. Mechanical Installation

Learning objectives

  • Execute the mechanical install in sequence to spec.
  • Maintain flashing, torque, and bonding quality throughout.

31.1 The mechanical sequence

IFC (International Fire Code): the model fire-safety code adopted (often with amendments) by most U.S. jurisdictions. For rooftop PV, it mandates setback widths and clear pathways on the roof so firefighters can operate safely around the array (see Ch 26).
  1. Layout per the approved plan, marking rafter locations and honoring IFC setbacks/pathways (Ch 26).
  2. Attachments: install flashed standoffs/feet into structure (Ch 24/26), each torqued to spec.

Metal step flashing slid under the upslope shingle course, with the mount and a sealant bead on top. Figure 31.2: Step flashing tucked under the upslope shingle course; mount and sealant over it. Water sheds over the flashing, never under.

  1. Racking: assemble and level rails; establish equipment bonding with UL 2703 hardware (WEEBs/clips, Ch 22).

Equipment-grounding lay-in lug with a toothed bonding washer biting between a module frame and a bare copper conductor. Figure 31.3: Equipment bonding: a listed lug / toothed washer bonds the module frame and rail, with a bare copper equipment-grounding conductor.

  1. Modules: set and secure with listed clamps at specified torque, maintaining the bonding path across the array.
  2. Conductor management: support wiring in UV-rated clips, off the roof surface, protected from abrasion.

31.2 Quality is in the repetition

Every penetration flashed, every bolt at torque, every bond made: there are no minor steps. A single unflashed foot leaks; a single loose clamp becomes a wind-loosed module. ⚠️ Torque-document with a calibrated tool; “hand-tight” is not a spec.

31.3 The mechanical sequence (and its quality triad)

 LAYOUT ─► ATTACH ─► RACK ─► SET MODULES ─► MANAGE WIRE
 (plan,    (flashed   (level  (listed clamps  (UV clips,
  setbacks, standoffs  rails,  at torque,      off the roof)
  rafters)  to struct, UL 2703 keep bonding)
            torqued)   bonding)
                    │
        every attachment point: FLASH ─ TORQUE ─ BOND

⚠️ Quality is the disciplined repetition of flash-torque-bond. One unflashed foot leaks; one loose clamp becomes a wind-loosed module; one missed bond breaks the grounding path. Torque with a calibrated tool and document it: “hand-tight” is not a spec. Torque values are product-specific; always consult the manufacturer’s installation instructions.

Calibrated torque wrench tightening a fastener on a roof-mounted PV foot on a composition-shingle roof. Figure 31.1: Torque every structural fastener to the manufacturer’s spec with a calibrated wrench (values are product-specific).

Chapter 31 summary

Lay out to plan and setbacks; install flashed, torqued attachments into structure; assemble level racking with UL 2703 bonding; set modules with listed clamps at torque; manage conductors off the roof. Quality is the disciplined repetition of flash/torque/bond on every point.

  • IFC (International Fire Code): model fire-safety code that sets rooftop PV setback and pathway requirements.
  • Flashed standoff/foot: a roof-penetrating mount sealed with step or counter-flashing so water sheds over, never under, the penetration.
  • UL 2703: the listing standard for integrated PV racking and bonding systems; hardware listed to it provides the equipment-bonding path across the array.
  • Listed clamp: a module-securing device evaluated and marked to a recognized standard (UL or equivalent), required by NEC for the bonding path.
  • Flash/torque/bond: the three quality actions required at every attachment point; each must be completed and documented.

Full definitions: Appendix A (glossary).

Practice Problems: Chapter 31

  1. What three quality actions must happen at essentially every attachment point?
  2. Why document torque with a calibrated tool rather than tightening by feel?
  3. What provides the equipment-bonding path across a modern racking system?
  4. What’s the consequence of a single loose module clamp in a high-wind event?

Solutions: Chapter 31

  1. Flash, torque, bond.
  2. Under- or over-torque both fail (leaks/loosening or stripped/cracked); a calibrated, documented torque is verifiable for QA and warranty.
  3. UL 2703-listed bonding hardware (WEEBs, clips, lugs) integrating the rails/clamps into the grounding path.
  4. The module can work loose and become a wind-launched hazard, plus a broken bond/electrical fault.