Electrical Conduit Types: PVC vs. EMT vs. RMC for Solar Installations
Reading time: ~12 min read
📋 Key Takeaways
- PVC conduit is nonmetallic, corrosion-resistant, and ideal for underground runs.
- EMT (Electrical Metallic Tubing) is lightweight, easy to bend, and common for indoor use.
- RMC (Rigid Metal Conduit) provides maximum physical protection for exposed or hazardous areas.
- NEC specifies burial depth requirements that vary by conduit type and location.
- UV resistance is critical for conduit exposed to sunlight.
Conduit selection is a decision that affects installation cost, labor time, code compliance, and long-term system reliability. In solar PV and generator installations, conduit must protect conductors from physical damage, UV exposure, moisture, and—in underground runs—soil pressure and groundwater. This guide compares the three most common conduit types—PVC, EMT, and RMC—with NEC fill calculations, burial depth requirements, UV resistance considerations, and a practical application guide for solar and generator installations.
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Conduit Types Overview
Rigid PVC Conduit (Schedule 40 and Schedule 80)
Polyvinyl chloride (PVC) conduit is a nonmetallic raceway available in Schedule 40 (standard wall) and Schedule 80 (heavy wall) configurations. It is the most economical conduit type and is widely used for underground and outdoor solar installations.
- NEC Article: Article 352 (Rigid PVC Conduit)
- Material: Extruded PVC plastic
- Sizes: 1/2" through 6" trade sizes
- Temperature range: -10°C to 75°C (14°F to 167°F)
- UV resistance: Good—suitable for continuous outdoor exposure
- Corrosion resistance: Excellent—immune to galvanic and soil corrosion
- Joining method: PVC solvent cement
- Physical protection: Moderate (Sch 40); High (Sch 80)
Electrical Metallic Tubing (EMT)
EMT is a thin-wall galvanized steel raceway widely used for indoor branch circuit wiring. It is lightweight, easy to bend, and requires no threading.
- NEC Article: Article 358 (Electrical Metallic Tubing)
- Material: Galvanized steel (also available in aluminum)
- Sizes: 1/2" through 4" trade sizes
- Temperature range: -40°C to 90°C
- UV resistance: Fair—galvanized coating degrades outdoors over time; requires additional protection for long-term exterior exposure
- Corrosion resistance: Moderate—suitable for dry indoor locations; not for direct burial or wet/corrosive environments
- Joining method: Setscrew or compression couplings and connectors
- Physical protection: Moderate—not approved for areas subject to severe physical damage
Rigid Metal Conduit (RMC)
RMC is a heavy-wall threaded metal conduit providing the highest level of physical protection. It is the premium choice for installations requiring maximum durability and mechanical protection.
- NEC Article: Article 344 (Rigid Metal Conduit)
- Material: Hot-dip galvanized steel (also available in aluminum, stainless steel, and red brass)
- Sizes: 1/2" through 6" trade sizes
- Temperature range: -40°C to 90°C and beyond
- UV resistance: Excellent—galvanized coating withstands continuous outdoor exposure
- Corrosion resistance: Good (galvanized steel); Excellent (aluminum or stainless for corrosive environments)
- Joining method: Threaded couplings and connectors
- Physical protection: Highest—approved for all locations including areas subject to severe physical damage
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 | Good | Fair | Excellent |
| Direct burial | Yes | Yes | No | Yes |
| Corrosion resistance | Excellent | Excellent | Moderate | Good |
| Weight | Light | Light | Medium | Heavy |
| Bending | Heat gun or fittings | Heat gun or fittings | Hand or mechanical bender | Mechanical/hydraulic |
| Joining method | Solvent cement | Solvent cement | Setscrew/compression | Threaded |
| Indoor use | Yes | Yes | Yes | Yes |
| Outdoor exposed | Yes | Yes | With caution | Yes |
| Underground | Yes | Yes | No | Yes |
| Areas of severe damage | No | Yes (with conditions) | No | Yes |
| Wet locations | Yes | Yes | No (per NEC 358.10) | Yes |
| Relative cost (per ft) | Lowest | Low | Medium | Highest |
NEC Conduit Fill Calculations
NEC Chapter 9, Table 1 establishes maximum fill percentages based on the number of conductors in the raceway:
| Number of Conductors | Maximum Fill Percentage |
|---|---|
| 1 conductor | 53% |
| 2 conductors | 31% |
| 3 or more conductors | 40% |
For conduits containing a combination of conductor sizes, use the 40% fill (3+ conductors) and calculate the total cross-sectional area of all conductors against the conduit's internal area.
Conductor Cross-Sectional Areas (THHN/THWN-2)
From NEC Chapter 9, Table 5:
| 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 (40% Fill)
From NEC Chapter 9, Table 4:
| Trade Size | PVC Sch 40 (sq. in.) | PVC Sch 80 (sq. in.) | EMT (sq. in.) | RMC (sq. in.) |
|---|---|---|---|---|
| 1/2" | 0.597 | 0.481 | 0.122 | 0.126 |
| 3/4" | 1.052 | 0.873 | 0.213 | 0.208 |
| 1" | 1.726 | 1.469 | 0.346 | 0.335 |
| 1-1/4" | 2.993 | 2.625 | 0.598 | 0.588 |
| 1-1/2" | 4.076 | 3.630 | 0.814 | 0.782 |
| 2" | 6.711 | 6.075 | 1.342 | 1.316 |
Values shown are the usable area at 40% fill (3+ conductors) from NEC Chapter 9, Table 4. Consult the full NEC table for complete data across all trade sizes.
Fill Calculation Example
A solar DC home run requires 6 conductors of #10 AWG THWN-2 in PVC Sch 40 conduit:
- Conductor area: 6 × 0.0211 = 0.1266 sq. in.
- 40% fill in 1/2" PVC Sch 40 = 0.597 sq. in.
- 0.1266 < 0.597—passes easily
- However, if conduit fill derating (NEC 310.15(C)(1)) also applies (6 current-carrying conductors = 0.80 factor), verify the conductor ampacity after derating is still adequate
For quick reference, NEC Annex C provides pre-calculated maximum conductor counts. For example, 1/2" EMT accepts 9 conductors of #12 AWG THHN at 40% fill.
Burial Depth Requirements (NEC Table 300.5)
NEC Table 300.5 specifies minimum cover requirements (depth from finished grade to the top of the conduit or cable) for underground installations 0 to 1000 volts. The burial depth depends on the wiring method and the installation location:
| Wiring Method | Direct Burial | PVC (Sch 40/80) | RMC | EMT |
|---|---|---|---|---|
| Residential (0-1000V), general | 24" | 18" | 6" | Not permitted |
| Non-residential (0-1000V), general | 24" | 24" | 6" | Not permitted |
| In or under 2" concrete | 18" | 18" | 6" | Not permitted |
| In or under 4" concrete | 12" | 12" | 6" | Not permitted |
| Under buildings | 0" (no cover required) | 0" | 0" | 0" (if not subject to damage) |
| Under streets/highways | 24" | 24" | 24" | Not permitted |
Source: NEC Table 300.5, 2023 NEC. Values represent minimum cover (top of conduit to finished grade). Trench depth must be deeper to accommodate conduit diameter. Verify against the NEC edition adopted in your jurisdiction, and note additional requirements for circuits over 1000V.
Burial Depth Notes
- Cover is defined as the shortest distance from the top surface of the conduit to the top surface of finished grade, concrete, or similar cover
- Trench depth must be deeper than the cover requirement to accommodate the conduit diameter
- For residential installations, PVC at 18" is the most common underground choice for solar PV DC runs and generator feeders
- RMC can be buried at only 6" cover but is significantly more expensive than PVC; use RMC where physical damage is a concern or where shallow burial is required
- EMT is NOT approved for direct burial under any circumstances (NEC 358.12)
- Mark underground conduit runs with warning tape placed 6–12 inches above the conduit
UV Resistance and Outdoor Exposure
For solar installations, conduit is frequently exposed to direct sunlight for the system's lifetime (25+ years). UV degradation is a critical factor:
- PVC: UV-stabilized formulations provide good long-term resistance. Schedule 80 PVC has thicker walls that better withstand UV degradation. Discoloration (yellowing) may occur but does not significantly affect structural integrity. Always verify the PVC is listed and marked for outdoor use.
- EMT: The galvanized zinc coating provides moderate UV protection but will weather and eventually corrode in continuous outdoor exposure. EMT used outdoors should be painted or protected, and is generally not recommended for long-term exterior solar installations. NEC 358.10(B)(2) requires EMT installed in wet locations to be listed as "rain-tight."
- RMC: Hot-dip galvanized RMC provides excellent UV resistance and is the preferred metal conduit for outdoor exposed installations. The zinc coating self-heals minor scratches through galvanic action. For maximum longevity in coastal or corrosive environments, consider aluminum or stainless steel RMC.
Solar Rooftop Conduit Installation
When running conduit across rooftops for solar PV installations:
- PVC Sch 80 is commonly used for exposed rooftop runs due to UV resistance and impact resistance
- Support conduit every 3 feet for PVC (NEC 352.30) and every 10 feet for metal conduit
- Use UV-rated conduit straps and hangers
- Elevate conduit above the roof surface to allow water drainage and reduce heat buildup (NEC 310.15(B)(2) rooftop temperature derating applies)
- For areas subject to foot traffic or maintenance access, use Sch 80 PVC or RMC for additional physical protection
- Seal all conduit penetrations through the roof with appropriate flashing and sealant
Cost Comparison
Costs vary by region, quantity, and trade size, but relative pricing is consistent:
| 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 |
Approximate material costs only. Does not include fittings, labor, or installation. Pricing varies by region and quantity.
Installed Cost Considerations
- PVC: Lowest material cost; solvent welding is fast but requires cure time; no special tools required; labor-efficient for straight runs
- EMT: Moderate material cost; hand bending is fast for small sizes; setscrew fittings are quick to install; no threading required; ideal for indoor branch circuits
- RMC: Highest material cost; requires threading equipment; heavy and labor-intensive to handle; threaded fittings are time-consuming; provides maximum durability
Application Guide for Solar and Generator Installations
Solar PV DC Array Wiring
- Rooftop exposed runs: PVC Sch 80 (UV resistance + impact resistance) or RMC (maximum protection in high-traffic areas)
- Underground (array to inverter): PVC Sch 40 at 18" (residential) or 24" (commercial) cover
- Through building penetration: PVC Sch 80 or RMC sleeve through roof/wall
- Inverter to combiner: PVC Sch 80 or EMT (if indoors)
Generator Installations
- Generator to transfer switch (above ground): RMC for the exposed portion near the generator (physical protection) transitioning to EMT or PVC for indoor runs
- Generator to transfer switch (underground): PVC Sch 40 at 18-24" cover
- Through wall penetration: RMC sleeve with weatherproof fittings
- Indoor wiring: EMT for branch circuits; PVC for wet areas
Service Entrance and Interconnection
- Utility interconnection: RMC for exposed service mast and weatherhead; PVC for underground service lateral
- Solar AC tie-in to main panel: EMT (indoor) or PVC Sch 80 (outdoor); RMC for service-entrance-rated portions
Installation Best Practices
PVC Installation
- Apply PVC primer before solvent cement for proper bonding
- Allow adequate cure time before pulling conductors (check cement manufacturer instructions)
- Expansion joints required for long straight runs (PVC expands/contracts ~3" per 100 ft per 50°F temperature change)
- Use PVC glue rated for the conduit material (not plumbing cement)
- Support every 3 feet (NEC 352.30)
- Pre-warm conduit in cold weather for easier bending and joining
- Use sweeping bends (long radius) to facilitate conductor pulling
EMT Installation
- Use a hand bender for sizes 1/2" through 1"; mechanical bender for larger sizes
- Deburr cut ends to prevent conductor damage during pulling
- Use rain-tight fittings for outdoor or wet locations
- Support every 10 feet and within 3 feet of each termination (NEC 358.30)
- Tighten setscrew fittings securely; consider using compression fittings for critical applications
- Bond all metal conduit to the equipment grounding system
- Do NOT use EMT in direct burial, concrete-encased underground, or areas subject to severe physical damage
RMC Installation
- Use a power threader for efficient threading; hand threading is possible but slow
- Apply thread sealant or conductive paste to threaded joints for corrosion protection
- Ream and deburr all threaded ends
- Support every 10 feet and within 3 feet of each termination (NEC 344.30)
- Use galvanized fittings and couplings; do not mix metals without proper bonding
- Bond to grounding system; RMC can serve as the equipment grounding conductor per NEC 250.118 if properly installed
- For underground use, wrap threads with approved corrosion-protection tape
Other Conduit Types to Consider
- Intermediate Metal Conduit (IMC, NEC Article 342): Lighter than RMC but heavier than EMT; threaded installation; approved for all locations including direct burial at 6" cover. Good compromise between cost and protection.
- LFNC-B (Liquidtight Flexible Nonmetallic Conduit, NEC Article 356): Flexible, waterproof; used for final connections to generators and equipment requiring vibration isolation. UV-rated versions available.
- FMC (Flexible Metal Conduit, NEC Article 348): "Greenfield"; flexible metal conduit for indoor use; not for wet locations.
- ENT (Electrical Nonmetallic Tubing, NEC Article 362): Corrugated, flexible PVC; indoor use only (concealed in walls); not for outdoor or underground use.
Conduit Selection Checklist
- Determine installation environment: indoor, outdoor exposed, underground, wet, corrosive
- Verify NEC approval for the intended location (e.g., EMT not for burial or wet locations)
- Calculate conduit fill per NEC Chapter 9, Table 1
- Verify maximum conductor count against NEC Annex C tables
- Check burial depth per NEC Table 300.5 for underground runs
- Verify UV resistance for outdoor exposed installations
- Consider physical damage risk; use Sch 80 PVC or RMC where required
- Plan for thermal expansion in long PVC runs
- Select appropriate fittings: rain-tight for outdoor, sealing for underground
- Verify grounding and bonding requirements for metal conduit
- Coordinate with conductor derating for 4+ current-carrying conductors (NEC 310.15(C)(1))
- Consider future expansion—upsize conduit for pull room and future circuits
Conclusion
For most solar PV installations, PVC Schedule 40 (underground) and Schedule 80 (outdoor exposed) provide the best balance of cost, UV resistance, and ease of installation. RMC is the premium choice where maximum physical protection is needed or where shallow burial is required. EMT is ideal for indoor branch circuits and generator room wiring but is not suitable for outdoor or underground use. By matching the conduit type to the specific installation environment and performing proper NEC fill and burial depth calculations, installers ensure code-compliant, durable raceway systems that protect conductors for the 25+ year life of a solar installation.
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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. EMT is thin-wall metal tubing for indoor use, easy to bend but not for physical protection. RMC is thick-wall metal conduit providing maximum physical protection for exposed and hazardous areas.
How deep does conduit need to be buried?
NEC burial depths vary by conduit type and location. RMC requires 6 inches under residential driveways, EMT requires 18 inches, and PVC Schedule 40 requires 18 inches for direct burial. Always check local amendments to NEC requirements, as some jurisdictions require deeper burial.
Can PVC conduit be used in sunlight?
Schedule 40 and Schedule 80 PVC conduit is UV-resistant and can be used in direct sunlight. However, prolonged UV exposure can cause some degradation over decades. For maximum longevity in sunny locations, consider painting exposed PVC or using UV-rated formulations.
When should I use RMC instead of EMT?
Use RMC where physical protection is critical: exposed runs subject to impact, areas with vehicular traffic, hazardous locations, and where the conduit provides equipment grounding. EMT is suitable for indoor runs protected from physical damage where cost and ease of installation are priorities.
What conduit type is best for solar installations?
For solar, use PVC for underground DC runs (corrosion resistance and cost), EMT for indoor AC wiring (ease of installation), and RMC for exposed rooftop or ground-mount DC runs where physical protection is needed. Match the conduit type to each section's environmental conditions.
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