Pick the wrong conduit for a solar job and you find out at inspection — or worse, three summers later when a UV-chalked PVC run snaps at a coupling and takes a PV source circuit down with it. We supply all three of the workhorse raceways covered here — PVC, EMT, and RMC — and we have pulled thousands of feet of THWN-2 through every one of them. This is the comparison we wish every apprentice and every DIY solar owner read before the first trip to the supply house: what each raceway is, where the NEC lets you use it, what it costs, and how to size it with real Chapter 9 math.
Conduit Types Overview
Three raceways cover about 90% of residential and light-commercial solar and generator work: rigid PVC (Schedule 40 and Schedule 80, NEC Article 352), electrical metallic tubing (EMT, Article 358), and rigid metal conduit (RMC, Article 344). Each has a legitimate home on a PV job. Each also has places it will fail — mechanically, chemically, or in front of an inspector.
Rigid PVC Conduit (Schedule 40 and Schedule 80)
PVC is the default underground raceway in most of the country, and for good reason: it never rusts, it cuts with a hand saw, joints solvent-weld in seconds, and it costs a fraction of metallic conduit. Schedule 40 is the standard wall; Schedule 80 has roughly double the wall thickness and is what NEC 352.10(F) wants where the raceway is exposed to physical damage — think the vertical stub-up out of the ground to a combiner box or inverter pad, where a weed trimmer or a snow shovel will eventually find it.
The honest weaknesses: PVC expands and contracts roughly five times more than steel with temperature (NEC 352.44 requires expansion fittings on long straight runs — a 100-foot run can move over 4 inches between winter and summer), sunlight exposure requires sunlight-rated marking, and it cannot be used as an equipment grounding conductor. Every PVC run on a solar job needs a separate green or bare EGC pulled in, per NEC 250 and 690.45.
Electrical Metallic Tubing (EMT)
EMT is the thin-wall steel tubing that fills commercial interiors. It bends with a hand bender, joins with setscrew or compression fittings, and looks clean on a wall. We've run miles of 3/4-inch EMT between inverters and gutters on garage walls. Its limits are absolute, though: EMT is not rated for direct burial, and NEC 358.10 restricts it in wet locations unless fittings are listed for the condition and corrosion protection is adequate. On a rooftop, EMT cooks in the sun, condenses moisture inside, and the setscrew fittings rust. Use it indoors and in protected runs; do not let it see soil or standing water.
Rigid Metal Conduit (RMC)
RMC is galvanized thick-wall steel pipe — the heavyweight. It threads like plumbing pipe, shrugs off physical abuse, is sunlight- and burial-proof, and at just 6 inches of cover it has the shallowest burial depth in Table 300.5 for most applications. The price is weight, labor, and material cost: threading and bending RMC is slow, and the material runs several times the cost of PVC. We spec RMC for service masts, exposed runs subject to damage, and anywhere the AHJ or utility demands maximum physical protection.
Side-by-Side Comparison
| Characteristic | PVC (Sch 40) | PVC (Sch 80) | EMT | RMC |
|---|---|---|---|---|
| NEC Article | 352 | 352 | 358 | 344 |
| Material | PVC plastic | PVC plastic | Galvanized steel | Galvanized steel |
| Wall type | Standard | Heavy | Thin-wall | Thick-wall |
| Physical protection | Moderate | High | Moderate | Highest |
| UV resistance | Good (sunlight-rated only) | Good (sunlight-rated only) | Fair (fittings rust outdoors) | Excellent |
| Direct burial | Yes | Yes | No | Yes |
| Corrosion resistance | Excellent | Excellent | Moderate | Good |
| Weight | Light | Light | Medium | Heavy |
| Bending | Heat gun, hot box, or fittings | Heat gun, hot box, or fittings | Hand or mechanical bender | Mechanical/hydraulic bender |
| Joining method | Solvent cement | Solvent cement | Setscrew/compression fittings | Threaded |
| Indoor use | Yes | Yes | Yes | Yes |
| Outdoor exposed | Yes (Sch 80 where subject to damage) | Yes | With caution; wet-listed fittings required | Yes |
| Underground | Yes | Yes | No | Yes |
| Areas of severe damage | No | Yes (with conditions) | No | Yes |
| Wet locations | Yes | Yes | Restricted per NEC 358.10 | Yes (with corrosion protection) |
| Equipment grounding | Separate EGC required | Separate EGC required | Can serve as EGC with listed fittings | Can serve as EGC |
| Relative cost (per ft) | Lowest | Low | Medium | Highest |
NEC Conduit Fill Calculations
Conduit fill is not a suggestion. Overfilled conduit cooks conductors, makes pulls brutal, and fails inspection. NEC Chapter 9, Table 1 sets the maximum fill percentages; Tables 4 and 5 give you the areas to work with.
| Number of Conductors in Raceway | Maximum Fill Percentage |
|---|---|
| 1 conductor | 53% |
| 2 conductors | 31% |
| 3 or more conductors | 40% |
Note the trap in that table: two conductors get less allowable fill (31%) than three (40%). Two round cables pack inefficiently. The equipment grounding conductor counts as a current-carrying conductor for fill purposes per NEC Chapter 9, Table 1 notes — include it in every fill calculation.
Conductor Cross-Sectional Areas (THHN/THWN-2)
From NEC Chapter 9, Table 5 — the values you multiply by conductor count:
| Wire Size | Area (sq. in.) | Wire Size | Area (sq. in.) |
|---|---|---|---|
| 14 AWG | 0.0097 | 2 AWG | 0.1158 |
| 12 AWG | 0.0133 | 1 AWG | 0.1562 |
| 10 AWG | 0.0211 | 1/0 AWG | 0.1855 |
| 8 AWG | 0.0366 | 2/0 AWG | 0.2223 |
| 6 AWG | 0.0507 | 3/0 AWG | 0.2679 |
| 4 AWG | 0.0824 | 4/0 AWG | 0.3237 |
Conduit Internal Areas at 40% Fill (3+ Conductors)
From NEC Chapter 9, Table 4 — usable area per raceway at the 40% fill limit:
| Trade Size | PVC Sch 40 (sq. in.) | PVC Sch 80 (sq. in.) | EMT (sq. in.) | RMC (sq. in.) |
|---|---|---|---|---|
| 1/2" | 0.114 | 0.087 | 0.122 | 0.125 |
| 3/4" | 0.203 | 0.164 | 0.213 | 0.220 |
| 1" | 0.333 | 0.275 | 0.346 | 0.355 |
| 1-1/4" | 0.581 | 0.495 | 0.598 | 0.610 |
| 1-1/2" | 0.794 | 0.684 | 0.814 | 0.829 |
| 2" | 1.316 | 1.150 | 1.342 | 1.363 |
Notice what Schedule 80 costs you: the thicker wall shrinks the interior, so a 1-inch Sch 80 PVC run holds roughly 17% less conductor area than Sch 40. On borderline fills, jumping to Sch 80 for the physical protection may force you up a trade size. Check both numbers before you order.
Fill Calculation Example
A real rooftop example: two PV source circuits plus ground in one raceway — four 10 AWG THWN-2 current-carrying conductors and one 10 AWG EGC. Five conductors at 0.0211 sq. in. each totals 0.1055 sq. in. Against the table: 1/2-inch EMT allows 0.122 sq. in. at 40% — it fits, with about 14% headroom. Add a third circuit later and you are at seven conductors, 0.1477 sq. in., and the same conduit fails. We size one step up — 3/4-inch — on nearly every solar run for exactly this reason. Empty conduit is cheap; re-piping a finished wall is not.
One more derating reminder for rooftops: raceway fill is only half the math. Conductors in conduit on a sun-exposed roof see ambient temperatures that trigger NEC 310.15(B) correction factors — a black EMT run on a July roof can sit 30°C above ambient. Cross-check ampacity with our NEC wire sizing guide and the wire ampacity chart before finalizing conductor size, and use the conduit fill chart for quick field lookups.
Burial Depth Requirements (NEC Table 300.5)
Cover depth — measured from finished grade to the top of the raceway — for 0–1000V circuits:
| Location / Condition | Direct Burial Cable | PVC (Sch 40/80) | RMC | EMT |
|---|---|---|---|---|
| General, not subject to vehicular traffic | 24" | 18" | 6" | Not permitted |
| Residential branch circuits ≤120V, ≤20A, GFCI-protected | 12" | 12" | 6" | Not permitted |
| In or under 2" concrete slab | 18" | 18" | 6" | Not permitted |
| In or under 4" concrete slab | 12" | 12" | 6" | Not permitted |
| Under buildings (in raceway) | 0" (in raceway) | 0" | 0" | Not permitted |
| Under streets, highways, driveways | 24" | 24" | 24" | Not permitted |
That 6-inch RMC cover depth is why we still trench rigid steel for short generator or PV runs under tight schedules — half the digging, half the backfill. But the moment the run crosses a driveway, everything goes to 24 inches regardless of raceway. I've seen a crew pour a 4-inch slab over a 12-inch-deep PVC run and get red-tagged because the inspector measured cover at the slab edge where grading had dropped it to 9 inches. Measure depth after final grading, not after the trench.
UV Resistance and Outdoor Exposure
PVC sold as electrical conduit is formulated and marked for sunlight resistance — look for "sunlight resistant" in the print string — but it still chalks and loses impact strength over decades of exposure. Schedule 80 buys wall thickness and time. EMT's galvanized coating weathers, and its fittings are the weak point: setscrew fittings outdoors corrode and lose continuity, which is a grounding failure waiting to happen. RMC with threaded couplings is the set-and-forget answer for exposed runs. On rooftops specifically, NEC 690.31 and 352/358 support requirements (generally within 3 feet of boxes and every 10 feet for EMT, every 3 feet per Table 352.30 for PVC in some sizes — verify against the current code cycle) plus expansion joints on long PVC runs are where inspections get failed. Support spacing for PVC tightens as temperature rises; the Table 352.30 values assume a specific ambient.
Solar Rooftop Conduit Installation
Rooftop PV raceways live in the harshest environment on the job: 150°F+ surface temperatures, standing water after storms, and constant UV. Our standard rooftop spec, built from warranty callbacks: Schedule 80 sunlight-rated PVC or RMC for any run subject to physical damage, expansion fittings on PVC runs over 20 feet, straps within 3 feet of every box and per Table 352.30 thereafter, and conductors sized with NEC 310.15(B) ambient correction plus the 310.15(B)(3)(c) rooftop adder where it applies. Inside the attic, transition to EMT for the homerun to the inverter — it bends clean, grounds itself with listed fittings, and stays out of the heat. Terminate rooftop runs into a listed junction box or a Soladeck-style flashed enclosure like the Conext XW conduit box family of accessories; every roof penetration gets proper flashing, no exceptions.
For conductor selection inside the raceway, PV Wire versus USE-2 versus THHN matters as much as the pipe around it — the solar wire and cable guide breaks that down. Grounding and bonding of metallic raceways on PV systems falls under NEC 690.43 and Article 250 — see the solar grounding and bonding guide.
Cost Comparison
Material-only ranges per foot, 2026 supply-house pricing. Fittings, cement, straps, and labor typically double the installed number:
| Conduit Type | 1/2" (per ft) | 1" (per ft) | 2" (per ft) | Relative Cost Index |
|---|---|---|---|---|
| PVC Sch 40 | $0.50–$1.00 | $1.00–$2.00 | $3.00–$5.00 | 1.0 (baseline) |
| PVC Sch 80 | $0.75–$1.50 | $1.50–$3.00 | $4.50–$7.50 | 1.5 |
| EMT | $1.00–$2.00 | $2.50–$4.50 | $8.00–$14.00 | 2.5 |
| RMC (galvanized) | $3.00–$5.00 | $6.00–$10.00 | $18.00–$30.00 | 6.0 |
Material cost is a rounding error next to labor. A 3/4-inch PVC run and a 3/4-inch RMC run differ by maybe $2 a foot in material, but the RMC run takes a journeyman with a threader three times as long. Choose the raceway the environment demands; do not save $60 on pipe and lose $600 in callbacks.
Application Guide for Solar and Generator Installations
Solar PV DC Array Wiring
Array to combiner or inverter: Sch 80 PVC or RMC for exposed rooftop runs, EMT for interior homeruns, PVC Sch 40/80 underground for ground-mount arrays. All DC source circuits in metal raceways on the roof should be bonded per NEC 690.43, and DC circuits inside a building must run in metal raceways or MC cable per NEC 690.31(G) — EMT earns its keep here.
Generator Installations
Generator to transfer switch runs are short, exposed, and vibration-prone. We spec liquidtight flexible metal conduit (LFMC, Article 350) for the final 18–24 inches to the genset to absorb vibration, with RMC or Sch 80 PVC for the straight runs. Underground feeders to a pad-mounted generator go in Sch 40 PVC at 18 inches, with Sch 80 for the stub-up. Pair the raceway plan with the right disconnect — the disconnect and overcurrent protection guide covers NEC 690 and 445 requirements, and a listed safety switch like the DU221RB 60A disconnect handles most residential generator and PV AC disconnect points.
Service Entrance and Interconnection
Service masts and utility-interconnection points are RMC territory in most jurisdictions — the mast must carry the service drop's mechanical load, and only threaded rigid conduit qualifies in many utility specs. Supply-side interconnections under NEC 705.12(A) typically land in RMC between the meter and the tap enclosure.
Installation Best Practices
PVC Installation
Deburr every cut — a sharp edge strips insulation during the pull. Use medium-clear cement rated for the temperature, give joints a quarter-turn as you push them home, and let them set before backfilling. Install expansion fittings anywhere a straight run exceeds 20 feet or crosses a structure joint. And pull a full-size EGC in every run; PVC gives you no fault path.
EMT Installation
Ream the inside of every cut; EMT burrs are razor sharp. Use compression fittings anywhere moisture is possible, setscrew only in dry interiors. Bend with the bender sized to the raceway — kinked EMT is scrap. Support within 3 feet of boxes and every 10 feet (NEC 358.30), and keep the total bends between pull points under 360 degrees (NEC 358.26) or plan a pull box.
RMC Installation
Cut threads full-depth, chase them clean, and coat field-cut threads with zinc-rich paint or listed cold-galv compound — a bare thread is where corrosion starts. Wrench-tighten couplings; a loose coupling is a grounding discontinuity. Ream every cut. The labor is real, which is why we prefab RMC assemblies on the bench whenever the run allows it.
Other Conduit Types to Consider
Three more raceways earn mentions on solar and generator work: LFMC (Article 350) for vibrating equipment connections and tight transitions; PVC-coated RMC for corrosive environments like coastal or agricultural sites, at a steep premium; and HDPE (Article 353) for directional-bored underground runs where trenching is not an option. Each has its place; none replaces the big three covered here.
Conduit Selection Checklist
- Underground, no traffic: Sch 40 PVC, 18" cover, Sch 80 stub-ups.
- Under driveway or street: any approved raceway at 24"; upsize for pull length.
- Rooftop exposed: Sch 80 sunlight-rated PVC or RMC; expansion fittings; correct support spacing.
- Interior garage/attic: EMT with compression fittings; 10-foot support spacing.
- Subject to physical damage: Sch 80 PVC or RMC only.
- Service mast: RMC per utility requirements.
- Corrosive/coastal: PVC, or PVC-coated RMC where metal is required.
- Vibration (generator final connection): LFMC, 18–24" whip.
Frequently Asked Questions
What is the difference between PVC, EMT, and RMC conduit?
PVC is a nonmetallic plastic conduit ideal for underground and corrosive environments; it requires a separate equipment grounding conductor. EMT is thin-wall metal tubing for dry or protected locations — easy to bend, but not rated for burial and not for severe physical protection. RMC is thick-wall threaded metal conduit providing maximum physical protection, the shallowest burial depths, and a grounding path in itself.
How deep does conduit need to be buried?
Under NEC Table 300.5 for 0–1000V circuits: PVC gets 18 inches of cover in general locations, RMC just 6 inches, and direct-burial cable 24 inches. Everything goes to 24 inches under driveways and streets. Measure from finished grade to the top of the raceway after final grading.
Can PVC conduit be used in sunlight?
Yes, provided it is listed and marked as sunlight resistant — electrical-grade PVC conduit is. Expect surface chalking over the years; it is cosmetic in most cases. Use Schedule 80 where the run is also exposed to physical damage, and install expansion fittings on long runs because PVC moves several times more than steel with temperature swings.
When should I use RMC instead of EMT?
Use RMC anywhere the raceway faces burial, severe physical damage, service-entrance duty, or prolonged outdoor exposure. EMT belongs indoors or in protected dry locations. If a snowplow, weed trimmer, or forklift can reach the conduit, it is RMC or Schedule 80 PVC — EMT will not survive the argument.
What conduit type is best for solar installations?
There is no single answer — there is a best answer per segment. Exposed rooftop runs: Sch 80 sunlight-rated PVC or RMC. Interior homeruns: EMT. Underground array feeders: Sch 40 PVC with Sch 80 stub-ups. DC circuits inside buildings: metal raceway or MC cable per NEC 690.31(G). Size every run with Chapter 9 fill math and NEC 310.15 temperature correction.
Does the ground wire count in conduit fill?
Yes. NEC Chapter 9, Table 1 notes require equipment grounding conductors to be counted in fill calculations. A circuit with three current-carrying conductors and one EGC is a four-conductor fill problem at the 40% limit.
Field Scenario: A Ground-Mount Feeder Done Right
One recent job ties this whole guide together. A 15 kW ground-mount array sat 90 feet from the shop building housing the inverter. The design: six source circuits in 10 AWG PV Wire from the array to a combiner at the array's edge, then a single underground feeder — four 4 AWG THWN-2 current-carrying conductors plus a 6 AWG EGC — in 1-1/4-inch Schedule 40 PVC at 18 inches of cover, with Schedule 80 stub-ups at both ends. The fill math: four 4 AWG at 0.0824 sq. in. plus one 6 AWG at 0.0507 totals 0.3803 sq. in.; 1-1/4-inch Sch 40 allows 0.581 sq. in. at 40%, leaving comfortable headroom for a future circuit. The stub-up into the combiner got a listed LB and an expansion coupling on the long straight run. Inside the building, the feeder transitioned to EMT for the final wall run to the inverter — clean bends, compression fittings, 10-foot strap spacing. Total raceway cost was under $400; total labor was a day and a half, most of it trenching. The inspector's only comment was a compliment on the expansion fitting, which he said he sees forgotten weekly. That is the standard to aim for: boring, correct, and inspection-proof.
Ready to Source Your Equipment?
We stock conduit bodies, boxes, fittings, and raceway accessories from brands like Kraloy, Allied Tube & Conduit, Topaz, and Arlington, plus the PV wire and THHN/THWN-2 to pull through them. Surge protection at the inverter and service rounds out the system — the SPD sizing guide covers that piece. Contractors: open a quote on your next bill of materials through Portlandia Electric Supply — our counter staff speaks NEC Chapter 9 fluently.
