Racking, Module Installation, and DC Wiring

Racking, Module Installation, and DC Wiring

This lab brings together structural work, electrical work, and safety discipline in a single, integrated task. By the end of the session your crew will have a mechanically sound, correctly wired, and fully labeled DC array ready for instructor inspection. Every step must be performed in sequence; do not skip ahead.

Lockout/Tagout Before You Touch Anything

Even though the training modules are non-energized or low-voltage simulation panels, you must establish lockout/tagout (LOTO) before the session begins and maintain it until the instructor authorizes energization. Apply a personal lock to every energy-isolating device associated with the training structure. Each crew member applies their own lock — never share a lock. Post the required tagout tags. This is not optional paperwork; LOTO violations result in an automatic restart of the affected task.

Fall Protection on the Roof Mockup

Anytime you are on or near the roof mockup, your fall-arrest harness must be donned, inspected, and connected to an anchor point rated for the load. Inspect the harness for cuts, frayed webbing, and proper buckle function before each use. Hard hat and safety glasses are required at all times on the mockup; gloves are required when handling module edges, conduit ends, and fasteners. A crew member on the ground acts as the safety checker and must visually confirm every fastener point is signed off before the next step proceeds.

Step 1 — Racking Layout and Structural Attachment

Begin with the manufacturer's installation instructions (MII) — they govern every spacing and torque requirement. Locate rafters using a stud finder and confirm each hit by probing with a finish nail before drilling. Mark rafter centers with a chalk line. Install flashing and standoffs (feet) at the spacing the MII specifies; typical residential flush-mount systems require feet on every other rafter or at intervals that keep rail deflection within limits, but always follow the specific product's table. Thread lag bolts through the flashing and standoff base. A properly sized pilot hole reduces split risk and ensures the lag threads fully into solid lumber — the MII will specify pilot-hole diameter. Torque each lag bolt to the value listed in the MII using a calibrated torque wrench; record the torque value and location on your documentation sheet. Have your safety checker initial the sheet before moving to the next foot.

Once all feet are set, snap rails into the mounting feet and secure them with the hardware provided. Rails must be level and co-planar; check with a level and tape measure. Splice rails according to the MII, leaving the required thermal-expansion gap.

Step 2 — Module Mounting and Bonding

Set each module into the rail channel. Mid clamps go between adjacent modules; end clamps secure the outer edge of each row. Torque clamps to the value in the MII — under-torquing allows modules to shift; over-torquing can crack frames. Many listed racking systems provide bonding through the clamp-to-rail contact, but verify using the MII and the clamp's listing. Where separate bonding hardware (such as a listed bonding washer or lug) is required, install it at every module. Bonding ensures all metal parts of the array are at the same electrical potential, which is essential for safety and for passing the bonding continuity check during inspection.

Route module leads carefully; do not allow cables to rest on sharp metal edges or touch the roof surface without a listed cable clip or wire management clip.

Step 3 — DC Conductor Routing and Termination

Plan your conduit run from the array home-run location to the combiner or inverter before cutting anything. Use weatherproof EMT or liquid-tight flexible conduit as appropriate for the segment. Calculate conduit fill before selecting conduit size — you will use the worked examples below for practice. Secure conduit with listed hangers or straps at intervals required by the applicable installation standard; as a general rule, supports are needed within a specified distance of every box and at regular intervals along the run (consult the code-required spacing for the conduit type you are using).

Pull THWN-2 conductors with wire lubricant on pulls of any significant length; do not pull dry on bends. Each student must personally land at least four conductors. Strip insulation to the depth indicated by the terminal's strip-gauge mark — no more, no less. Insert the conductor fully and tighten the terminal screw to the torque value marked on the equipment or given in the manufacturer's instructions, using a calibrated torque screwdriver. Under-torqued connections arc; over-torqued connections strip threads or damage conductors.

After all conductors are landed, use a multimeter set to DC volts to verify polarity at each source circuit before any connection to the inverter or combiner. Positive to positive, negative to negative. Record each reading on the checklist.

Step 4 — Labeling

NEC Article 690 requires specific labels at PV system components. Using the program's NEC 690 labels kit, attach all required labels at the combiner, disconnect, and any other required location. Labels must be legible, durable, and permanently attached. Photograph every labeled component for your documentation package; these photos are part of your deliverable.

Pre-Energization Checklist

Before calling for instructor sign-off, run through the program's DC installation inspection checklist in full: structural attachment verified, bonding continuity confirmed, polarity verified, conduit fill within limits, conduit supports at correct spacing, wire management complete, all labels attached and photographed. Only when every item is checked and signed may you call the instructor for the live walkthrough.

Safety Summary

• Maintain LOTO throughout; one lock per person.
• Harness connected before stepping onto the mockup.
• Sign off every fastener torque point before proceeding.
• Verify polarity before any connection to active terminals.
• Never energize without instructor authorization.