4.4 Raceways & Flexible Conduits (EMT, RMC, PVC, FMC)

4.4 Raceways & Flexible Conduits (EMT, RMC, PVC, FMC)

Exam Focus: Support spacing for EMT (Article 358), RMC (Article 344), PVC (Article 352), FMC/LFMC (Articles 348/350), 360° total bend rules, PVC expansion fittings under 352.44, and flexible conduit grounding limits under NEC 250.118.

Raceway systems serve two primary electrical safety functions: they provide mechanical protection for enclosed conductors and, in the case of metallic raceways, often act as an equipment grounding path. The Michigan Journeyman examination heavily tests raceway support intervals, total allowable bends, ground continuity rules, and environmental suitability.

---

General Raceway Rules: 360° Bend Limit

For ALL conduit systems (EMT, RMC, IMC, PVC, FMC, LFMC), the total equivalent bend angle between pull points (boxes, cabinets, or conduit bodies) must NOT exceed 360 degrees (the equivalent of four 90-degree quarter bends).

$\text{Total Bends} = \sum \theta_{\text{bends}} \le 360^\circ$

[!CAUTION] Exceeding 360° between pull boxes causes severe insulation burn-through during conductor pulling and violates NEC 358.26, 344.26, 352.26, and 348.26.

---

Electrical Metallic Tubing (EMT) — Article 358

EMT is an unthreaded thin-wall metallic raceway commonly used in commercial and industrial interior wiring.

1. Support & Securing Rules — NEC 358.30

• Must be securely fastened within 3 feet (900 mm) of each outlet box, junction box, cabinet, conduit body, or termination.
• Must be supported at intervals not exceeding 10 feet (3.0 m) along runs.
• Framing Exception: Where structural framing prevents securing within 3 feet, distance may be extended up to 5 feet (1.5 m).

2. Wet Location Connectors

In wet locations, all couplings and connectors must be listed raintight compression type (NEC 358.42).

---

Rigid Metal Conduit (RMC) — Article 344

RMC is a heavy-wall threaded metallic raceway providing maximum mechanical protection.

1. Threading Specifications — NEC 344.28

• Field threads must be cut using a standard NPT (National Pipe Taper) die with a taper of 3/4 inch per foot (1 in 16 taper).
• Threaded joints must be made up wrench-tight. Field-cut threads must be coated with an electrically conductive anti-corrosion compound.

2. Support Spacing — NEC Table 344.30(B)(2)

+-------------------------------------------------------------------------+
|                 RMC STRAIGHT RUN SUPPORT SPACING TABLE                  |
+------------------------------------+------------------------------------+ 
| Trade Size                         | Maximum Support Spacing            |
+------------------------------------+------------------------------------+
| 1/2 in. and 3/4 in.                | 10 Feet (3.0 m)                    |
| 1 in.                              | 12 Feet (3.7 m)                    |
| 1-1/4 in. and 1-1/2 in.            | 14 Feet (4.3 m)                    |
| 2 in. and 2-1/2 in.                | 16 Feet (4.9 m)                    |
| 3 in. and larger                   | 20 Feet (6.0 m)                    |
+------------------------------------+------------------------------------+

• RMC must be supported within 3 feet (900 mm) of each box or termination.

---

Rigid Polyvinyl Chloride Conduit (PVC) — Article 352

PVC is a rigid nonmetallic raceway resistant to moisture, chemicals, and soil corrosion.

1. Schedule 40 vs. Schedule 80 Applications (NEC 352.10)

• Schedule 40 PVC: Standard wall thickness approved for underground burial, concrete slabs, and aboveground areas not subject to physical damage.
• Schedule 80 PVC: Heavy wall thickness REQUIRED where conduit is exposed to physical damage (e.g., lower sections of exterior pole risers or exposed industrial walls).

2. Thermal Expansion & Contraction — NEC 352.44

• PVC has a high coefficient of thermal expansion ($4.06 \text{ inches per } 100 \text{ feet per } 100^\circ\text{F}$ temp change).
• Expansion Fittings Required: An expansion fitting must be installed whenever thermal expansion or contraction is expected to cause a length change of 0.25 inch (6 mm) or greater between fixed points.

3. Support Spacing — NEC Table 352.30

---

Flexible Metal Conduit (FMC) & Liquidtight Flexible Metal Conduit (LFMC)

FMC (Article 348) and LFMC (Article 350) provide flexibility for connecting motors, transformers, and vibrating equipment.

1. Support & Securing Rules (NEC 348.30 & 350.30)

• Must be secured within 12 inches (300 mm) of each box, cabinet, or fitting.
• Supported at intervals not exceeding 4.5 feet (1.4 m).
• Flexibility Exceptions: Unsupported lengths permitted up to 3 feet (900 mm) at terminals where flexibility is required for equipment vibration.

2. Equipment Grounding Limitations — NEC 250.118(5) & (6)

FMC or LFMC may serve as the sole equipment grounding conductor ONLY IF ALL of the following criteria are satisfied:

1. The flex conduit is terminated in listed fittings.
2. The trade size is 1/2 in. through 1-1/4 in.
3. The total ground return path length of flex in the circuit does NOT exceed 6 feet (1.8 m).
4. Overcurrent protection for the circuit is rated 20 amperes or less.

+-------------------------------------------------------------------------+
|             FMC / LFMC GROUNDING CONTINUITY DECISION MATRIX             |
+-------------------------------------------------------------------------+
|  Criteria Check:                                                        |
|  - Circuit Overcurrent Protection ≤ 20 Amperes?                         |
|  - Total Flex Length in Ground Path ≤ 6.0 Feet?                         |
|  - Listed Grounding Fittings Used?                                      |
+-------------------------------------------------------------------------+
                                     |
                  +------------------+------------------+
                  | YES                                 | NO
                  v                                     v
     Flex Armor Acts as Sole EGC           Equipment Bonding Jumper (EGC)
     (No internal wire EGC needed)         MUST be Installed (250.118)
+-------------------------------------------------------------------------+

[!WARNING] If the circuit breaker is rated 30A, 40A, or 50A, or if the flex length is 8 feet, you MUST pull an internal copper Equipment Grounding Conductor (EGC) through the flex!

---

Master Raceway Summary Comparison Table

---