PV Mounting Systems Field Checklist: Solar Array Ground Mount and Combiner Box for Solar Panels

At Mounting Systems, I handle commercial PV mounting-system orders. Before you click away: if you came here for snowboard mounting systems, I can't help you there. I've never mounted a snowboard in my life. This guide is about PV mounting systems—the rails, clamps, foundations, and electrical bits that hold a solar array together.

I've been handling these orders for eight years—since 2017. I've personally made—and documented—16 significant mistakes, totaling roughly $41,000 in wasted budget. Now I keep our team's pre-build checklist. This is that checklist.

Use it when you're ordering a solar array ground mount, replacing a roof system, or spec'ing out a combiner box for solar panels. Six checks. No fluff.

Check 1: Define the mounting system before you order hardware

If someone asks, 'what are the dwarf planets in our solar system?' the answer is Ceres, Pluto, Haumea, Makemake, and Eris. But knowing the names doesn't tell you their orbits. A 'ground mount' is the same way—it's a category, not a spec.

On a PV mounting-system order, I need to know: roof or ground, module make and model, module dimensions, wind/snow loads, and the design code that applies. I once priced a solar array ground mount using '200 modules' and a vague site address. When the drawings arrived, the module dimensions had changed. The clamps fit, but the rails were 47 mm too short across 160 modules. We returned 14 rails and lost a week.

What I mean is that the product name is the beginning, not the end. Bottom line: if your supplier only needs a size, ask for a drawing review before payment.

Check 2: Trust a stamped calculation, not a verbal 'it'll be fine'

A ground-mounted array is a structure. It needs wind calcs, snow calcs, and often a geotech report. I am not a structural engineer. I don't pretend to be one. If someone tells me 'this ground mount will handle 120 mph,' I ask for the stamped calc that says so. In the US, ASCE 7 is the usual structural standard; your local code might follow something else.

I went back and forth between ballasted and pile-driven for three weeks on one project. Ballasted was faster; pile-driven had a clear load path. In the end I chose based on geotech—not install speed. To be fair, ballasted systems are the right answer on some rooftops and even some ground sites. But 'it's heavy, so it won't fly' isn't a calculation.

A red flag for me: 'probably fine' from someone who isn't signing a PE seal. If you've ever explained a missed foundation to an owner, you know that sinking feeling. Take it from someone who has paid for it. The ground doesn't care about your schedule.

Check 3: Verify clamp compatibility and torque specs on the actual module

This one sounds like a no-brainer, but it's where I made my biggest single-order mistake.

On a 200-module order, every clamp was physically correct. The module profile had changed from the previous generation, and the torque spec in my installation manual no longer applied. I approved it myself. We caught it when the technician torqued a sample and the frame lip bent. $890 rework plus a one-week delay—all because I didn't re-read the manual after a module change.

The checklist: module frame width, clamp length, clamp range, bolt/washer spec, torque value, and the torque wrench calibration date. That last one is easy to skip. In my experience, a torque wrench can drift and start causing cracked frames before anyone notices.

Check 4: Size the string before you pick a combiner box for solar panels

The combiner box for solar panels is not a spare part to add later. It's an electrical assembly with overcurrent protection, and its ampacity has to match your string size. I've learned this the hard way.

String sizing is a cold-morning problem: module Voc goes up as temperature drops. My electrical engineer asks for the lowest expected ambient temperature and the inverter's absolute max input voltage, then we calculate max modules per string. We also run the conductor ampacity per NEC 690.8.

I once ordered a combiner box rated for six strings because that's what the sales contact said. The cold-temperature calculation said we only had five safe strings. The box was wrong—not because the box was bad, but because we picked it before the calc. $450 in restock shipping and a two-week schedule hit. Not my proudest moment.

Before you ask 'what combiner box fits?', the question should be 'what is the string plan?' The box follows the plan. If the number doesn't work, it doesn't work.

Check 5: Plan the solar array ground mount around the electrician

Here's the step most people ignore: plan the ground-mount layout for service access, not just module alignment.

A solar array ground mount can look perfect from above and still be unusable when the combiner box is tucked under a rail mid-row, facing the wrong direction. The cover opens, but you can't reach the lugs without your chest against a module. It took two service calls to teach me that. The first time I blamed the layout; the second time I blamed myself.

What I mean is that the mounting system has to support maintenance—not just PV panels. Leave access paths around electrical boxes, orient covers so they open without obstruction, and keep ground-mounted conduit out of the grass where weed eaters can hit it. This might conflict with the instinct to pack in more modules. That's okay. A 2% utilization loss is cheaper than a service call when a fuse needs replacing.

Take it from someone who has disassembled a row of modules just to open an exterior disconnect: design for the human who will touch it at 4 p.m. in a rainstorm.

Check 6: List the small accessories before you post the PO

Rails, clamps, mount posts—then the small stuff. End clamps, mid-clamps, splice plates, bolt kits, washers, grounding lugs, bonding straps. The manufacturer's BOM often lists these as separate line items. Don't assume they're included.

I once approved a roof system where every structural piece was right, but the stainless steel washers for the rail-to-foot connections weren't purchased. 38 pallets of material, one missing $24 box. Freight charge to send it later: $380. It felt absurd.

My process now is simple: I copy the entire BOM from the design into the PO. Not a ballpark list—every line. Then I check it against the stamped drawing. If the drawing says M8 bolts with flanged washers, I make sure the PO says the same. This is the boring part of the job, but it's the part that keeps the crew working.

Now the mistakes I don't want you to repeat

If I had to summarize eight years into a short list, it would look like this:

• Ordering clamps before confirming the exact module frame profile. The clamp family might be right; the torque spec might not.
• Treating a solar array ground mount as a 'ground pile kit' without a stamped structural calc.
• Choosing a string size and then trying to fit a combiner box for solar panels around it.
• Forgetting bonding. A PV mounting system is also a grounding path. UL 2703 covers this; your AHJ probably has questions.
• Skipping the revised manual after a module manufacturer makes a 'small update.'

To be fair, you could do all these right and still find a problem at the end. That's why I keep the checklist. It took me four years and about 150 orders to understand that the checklist isn't about catching careless people. It's about catching the things that looked fine at the time.

If I only left you with one line: the checklist is only as good as the one check you decide to skip. Skip nothing.