Conduit Types
The different conduit materials and forms available, their appropriate applications, and how to fabricate conduit alternatives when manufactured options are unavailable.
Why This Matters
Conduit is mechanical protection for electrical wire. Without it, wire in exposed or hazardous locations is vulnerable to physical damage, rodents, moisture, UV degradation, and accidental contact. With it, wire is safe for decades, and the installation can be modified simply by pulling out old wire and pulling in new.
In a rebuilding scenario, manufactured conduit may be scarce. Understanding the alternatives — what properties conduit must have, what can substitute, and how to improvise — means your wiring can be properly protected regardless of supply chain limitations.
Metal Conduit Types
Rigid Metal Conduit (RMC): Heavy-wall steel tube with threaded ends. The most robust conduit available. Used where maximum physical protection is needed: exposed industrial locations, areas where conduit may be hit by vehicles or machinery, underground direct burial, concrete encasement.
Properties:
- Wall thickness: 2–3mm steel
- Requires threading for connections (hand threader or power threading machine)
- Very heavy — structural support needed for long horizontal runs
- Provides equipment grounding path through the metal (no need for separate ground wire in most cases)
- Galvanized exterior for corrosion resistance; stainless available for highly corrosive environments
Intermediate Metal Conduit (IMC): Thinner wall than RMC but still threaded. Used similarly to RMC but where maximum protection isn’t required. Lighter and cheaper than RMC.
Electrical Metallic Tubing (EMT): Thin-wall steel or aluminum tubing. Not threaded — uses set-screw or compression fittings. Most common metal conduit for commercial and residential use. Works for concealed and exposed indoor applications; outdoor use only in weatherproof fittings; not suitable for direct burial unless specifically rated.
Properties:
- Wall thickness: 0.9–1.3mm
- Much lighter than RMC/IMC
- Set-screw fittings quick to install but less secure than threaded; compression fittings better for outdoor
- Grounding path through the metal (must use listed fittings that maintain continuity)
Flexible Metal Conduit (FMC) / “Greenfield”: Interlocking spiral steel strip forming a flexible tube. Used for connections to equipment that vibrates or for the final 1–2 feet of connection to fixed equipment where rigid conduit would be impractical. Not for long runs — too much friction for wire pulling. Not weatherproof without liquid-tight cover.
Liquid-tight Flexible Metal Conduit (LFMC): Flexible metal conduit with a thermoplastic outer jacket. Weatherproof and suitable for outdoor and wet locations. Common final connection to outdoor equipment (AC units, pumps).
Non-Metal Conduit Types
PVC Conduit (rigid): The most common non-metal conduit. Inexpensive, lightweight, corrosion-proof, easy to work with. Available in thin-wall (Schedule 20/40) and heavy-wall (Schedule 80) versions.
Properties:
- Excellent corrosion and chemical resistance
- Cannot be bent by hand — requires heat bending (heat gun or heat box)
- Glue-joined using PVC cement solvent welding (fast and permanent)
- Not a grounding path — must include separate green or bare ground wire in conduit
- Becomes brittle in cold weather (impact resistance decreases below -10°C)
- Expands and contracts significantly with temperature (10mm per 10°C per meter is not uncommon)
- UV resistance: use UV-rated gray/dark PVC for exposed outdoor use
PVC conduit bending: Heat 200–300mm section to be bent until soft (30–60 seconds with heat gun). Bend over a form or by hand to desired angle. Hold until cool (1–2 minutes). For multiple bends, plan bends in order — future bends soften nearby sections.
HDPE conduit: High-density polyethylene conduit. More impact-resistant than PVC, better cold-temperature performance, suitable for direct burial and horizontal directional drilling. Used for long-distance underground runs. Joined with couplings or heat fusion.
Fiberglass conduit: Highest temperature and chemical resistance. Used in refineries, chemical plants, extreme environments. Not commonly needed in rebuilding scenarios.
Flexible Non-Metal Conduit
ENT (Electrical Non-metallic Tubing): Corrugated PVC or nylon flexible conduit. Can be bent by hand (but springs back to straight). Used for concealed wiring in walls and ceilings where some flexibility is needed. NOT for exposed locations or outdoors.
Liquid-tight flexible non-metallic (LFNC): Smooth or corrugated plastic flexible conduit with outer liquid-tight jacket. Good for outdoor and wet applications where flexibility is needed but metal isn’t suitable.
Improvised and Alternative Conduit
When manufactured conduit is unavailable, these alternatives can provide mechanical protection:
Bamboo conduit:
- Hollow bamboo stems: straight sections make natural conduit
- Cut nodes out of the inside (bamboo cane drill or long thin chisel)
- Join sections with sleeve joints: wrap joint area with wire, seal with pitch or tar
- Excellent mechanical protection; poor moisture resistance (seal with tar or varnish inside and out)
- Provides no grounding path; must include ground wire
Ceramic or clay pipe sections:
- Terra cotta drain tile: available in many regions, highly durable
- Cut to length with masonry saw
- Join sections with mortar or clay
- Suitable for underground runs; UV-proof; provides no grounding
- Heavy but virtually permanent
Metal pipe (plumbing grade):
- Galvanized iron pipe or copper pipe
- Standard plumbing fittings available
- Threaded joints, elbows, tees standard
- Provides equipment grounding (same as electrical conduit)
- Use pipe threading dies to thread cut ends
- Expensive if copper; iron rusts if not galvanized
Metal trays and channels:
- Reclaimed metal channel (C-channel, box section) with cable lay-in and cover plate
- Bolted together, mounted to wall
- Functional as wireway for multiple cables
- Ground path if metal-to-metal connection maintained
Fittings and Accessories
Every conduit system relies on fittings — couplings, elbows, junction boxes, connectors:
Couplings: Join two lengths of conduit. Must match conduit type (threaded for RMC, compression for EMT, glue for PVC).
Elbows: Pre-bent 90° sections for turns. Available in various radii; larger radius = easier wire pulling.
Junction boxes: Metal or plastic boxes at intervals for pulling wire and making connections. Required by code at maximum intervals and where circuits branch.
Conduit bodies (LB, LL, LR, T): Accessible fittings for 90° turns and T-junctions in conduit runs. Small internal space; wire can be pulled in but connections typically made in full junction boxes.
Locknuts and bushings: Secure conduit to box wall. Bushing protects wire insulation at conduit end. Both required at every box entry.
Selection Summary
| Application | Recommended conduit |
|---|---|
| Exposed indoor (workshop, barn) | EMT or rigid PVC |
| Outdoor above-ground | Rigid PVC (schedule 40) or LFMC for flexible sections |
| Underground direct burial | Rigid PVC (schedule 40), HDPE, or RMC |
| Concrete encasement | RMC or rigid PVC |
| Equipment connections (vibrating) | LFMC or LFNC |
| Concealed in walls | ENT, EMT, or rigid PVC |
| Corrosive environments | PVC, fiberglass, or 316 stainless RMC |
The right conduit for each location ensures the wiring inside lasts the full service life of the installation, can be modified without structural disturbance, and provides the mechanical and electrical protection the wiring needs.