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newSchoolWorks.com › VoTechWorks › Building & Construction › Electrical › Electrical Capstone Project: Integrated Wiring and Systems Build › Lesson 2
BLD-ELEC05-08 · Lesson 2 · 96 clock hours · lab

Conduit Fabrication, Rough-In, and Box Installation

Objective. Students will fabricate and install a complete conduit system—including at least two stub-ups, one three-bend saddle, one offset, and all required junction and device boxes—on the program's full-scale wall-frame mockup, achieving dimensional accuracy within ±1/4 inch and full NEC support-spacing compliance.

Conduit Fabrication, Rough-In, and Box Installation

This lab brings together every layout and bending skill you have developed and applies them to a full-scale wall-frame mockup. By the end of the session you will have a complete conduit system—correctly spaced, accurately bent, properly filled, and ready for a simulated municipal rough-in inspection.

Safety First

Before picking up a tool, put on your PPE: safety glasses, work gloves, and hard hat. EMT cut ends are razor-sharp; always ream every cut end with a conduit reamer before threading wires or touching the edge with bare skin. When using a fish tape, keep hands clear of the reel and never feed tape toward an energized circuit. Even though the mockup is de-energized, treat the megohmmeter leads as you would a live meter—the instrument applies a test voltage that can startle or injure. Inspect all hand tools before use; a bent bender shoe or cracked handle changes your bend geometry and can slip.

For this lab the mockup is de-energized, so lockout/tagout is not required—but your instructor will review the procedure because it applies to every real rough-in job where existing circuits may be live nearby.

Laying Out Box Locations

Accurate layout is the foundation of clean rough-in work. Start by snapping a chalk line at the standard mounting height for device boxes (typically measured to the center of the box or to the bottom of the box, depending on local practice and your approved routing plan). Use a tape measure and torpedo level to position each box so its face will land flush with the finished wall surface once drywall is applied—account for the drywall thickness in your setback. Secure metallic outlet, switch, and junction boxes to studs using the manufacturer's approved fasteners; a box that rocks under hand pressure will fail inspection.

Before moving on, complete your box-fill calculation for every box. The NEC specifies the volume allowance for each conductor, device, clamp, and equipment-grounding conductor entering the box. If your calculated fill exceeds the box's listed cubic-inch capacity, you must upsize the box or reduce conductors. Record every calculation and call for instructor sign-off before bending conduit.

Bending EMT

All bends must be fabricated with the correct hand bender shoe for the conduit size—use the 1/2-inch shoe for 1/2-inch EMT and the 3/4-inch shoe for 3/4-inch EMT. Mix-ups crush the conduit wall and create a fail.

Stub-up: Place the arrow mark on the bender at the desired height line on the conduit and apply smooth, steady foot pressure until you reach 90°. Verify the stub height with a tape measure.

Offset: An offset uses two equal bends to clear an obstruction. Determine the offset depth and select the matching bend angle (common choices are 22°, 30°, or 45°). The shrink per inch of offset depth changes with angle—record the shrink multiplier for your chosen angle on your bend log sheet and subtract it from your first-mark measurement. Both bends must be in the same plane; use the conduit level to check.

Three-bend saddle: A three-bend saddle clears a round or rectangular obstacle. Mark the center of the obstacle on the conduit. The center bend is 45°; the two outer bends are each 22½°. The spacing between marks depends on the obstacle height—your NCCER module provides the formula. All three bends must align in one plane.

Back-to-back (or back-to-back 90°): Two stub-ups facing opposite directions; the distance between the arrows equals the center-to-center span you need.

Log every arrow mark, reference mark, and gain value before and after each bend. The instructor will measure every finished bend. Any bend outside the ±1/4-inch tolerance must be re-fabricated—kinked or flattened conduit is never acceptable.

Installing Conduit and Pulling Conductors

Secure conduit to the structure with approved straps or hangers. The NEC requires support within a specified distance of every box or fitting and at regular intervals along the run—verify the maximum support spacing for EMT in your NEC codebook and mark your strap locations before drilling. Conduit that sags between supports fails inspection.

Before pulling wire, verify conduit fill. The NEC limits the total cross-sectional area of conductors to a percentage of the conduit's interior area: 53% for one conductor, 31% for two conductors, and 40% for three or more. Use the wire and conduit tables in the NEC Annex to confirm compliance.

Feed your fish tape through the conduit, attach conductors, and pull smoothly—no jerking. Maintain correct color coding: black or red for ungrounded (hot) conductors, white or gray for grounded (neutral), and green or bare copper for equipment grounding conductors. Strip conductors to the correct length for each termination (device manufacturers mark the strip gauge on the back of the device). Use approved connectors and locknuts to secure conduit to boxes; hand-tighten, then give a quarter turn with pliers.

Install all device and junction box covers before testing.

Testing

After termination, perform two tests on every circuit:

1. Continuity test: Confirms that the circuit path is complete with no open connections.

2. Megger (insulation resistance) test: The megohmmeter applies a DC test voltage between conductors and between conductors and ground. A reading of at least 1 MΩ is required; a lower reading indicates damaged insulation or a fault. Log every reading on the project test-record form.

Any circuit that fails either test must be de-terminated, the fault found, corrected, and the test repeated.

The Rough-In Inspection

Your instructor uses a pass/fail checklist modeled on a real municipal rough-in inspection. Every item must pass: box heights within ±1/4 inch, conduit support spacing within NEC limits, conduit fill within allowed percentage, correct conductor color coding, continuity confirmed, and insulation resistance ≥1 MΩ. A single failure means you correct the item and call for re-inspection—just as you would on a real job site.

Key terms8

EMT (Electrical Metallic Tubing)A lightweight steel conduit, thin-walled and not threaded, connected with set-screw or compression fittings; commonly used in commercial and light industrial wiring.
Box-fill calculationAn NEC-required calculation that adds the volume occupied by each conductor, device, clamp, and grounding conductor in a box and compares the total to the box's listed cubic-inch capacity.
Conduit fillThe percentage of a conduit's interior cross-sectional area occupied by conductors; NEC limits are 53% for one wire, 31% for two, and 40% for three or more.
Three-bend saddleA conduit bend sequence—center bend at 45°, two outer bends at 22½° each—used to clear a round or rectangular obstacle while keeping the conduit run in one plane.
Gain (shrink)The amount a conduit run is effectively shortened when a bend is made; gain must be subtracted from layout measurements to achieve the correct finished dimension.
Megohmmeter (megger)A test instrument that applies a high DC voltage between conductors or between conductors and ground to measure insulation resistance; values below 1 MΩ indicate a potential fault.
Rough-in inspectionA mandatory building-department inspection performed after framing, conduit, and boxes are installed but before walls are closed, confirming code compliance before work is concealed.
Conductor color codingThe NEC convention for identifying wire function by insulation color: black or red for ungrounded (hot), white or gray for grounded (neutral), and green or bare copper for equipment grounding.

Worked examples4

1. Box-fill calculation: A 4-inch square metallic box has a listed volume of 21.0 cubic inches. The box contains four 12 AWG conductors entering from outside (two hots, one neutral, one ground), one device (single-pole switch), and one internal cable clamp. Each 12 AWG conductor has an NEC volume allowance of 2.25 cubic inches. Does the box have sufficient volume?
  1. Count conductors: 4 conductors entering from outside = 4 × 2.25 = 9.00 in³
  2. Count device allowance: 1 device = 2 conductor allowances = 2 × 2.25 = 4.50 in³
  3. Count clamp allowance: 1 internal clamp group = 1 conductor allowance = 1 × 2.25 = 2.25 in³
  4. Count equipment grounding conductors: all EGCs together count as 1 conductor allowance = 1 × 2.25 = 2.25 in³
  5. Total fill = 9.00 + 4.50 + 2.25 + 2.25 = 18.00 in³
  6. Compare to box capacity: 18.00 in³ ≤ 21.0 in³
Answer: The total required volume is 18.00 cubic inches, which is within the 21.0 cubic-inch box capacity. The box passes fill requirements.
2. Offset calculation: You must offset 1/2-inch EMT 4.5 inches deep to clear a beam. You choose a 30° bend angle. The shrink per inch of offset depth at 30° is approximately 1/4 inch (0.25 in/in). How much must you subtract from the first-mark measurement, and what is the total shrink?
  1. Identify offset depth: 4.5 inches
  2. Identify shrink multiplier for 30°: 0.25 inch per inch of offset depth
  3. Calculate total shrink: 4.5 × 0.25 = 1.125 inches, round to 1-1/8 inches for practical use
  4. Subtract total shrink from the first-mark dimension on your conduit before making the first bend
Answer: Total shrink is approximately 1-1/8 inches (1.125 in). Subtract this from your first-mark measurement so the finished offset lands at the correct location.
3. Conduit fill: You are installing three 12 AWG THWN conductors in 1/2-inch EMT. The interior cross-sectional area of 1/2-inch EMT is 0.304 square inches. Each 12 AWG THWN conductor has a cross-sectional area of 0.0133 square inches. Is the fill within the NEC 40% limit for three or more conductors?
  1. Calculate total conductor area: 3 × 0.0133 = 0.0399 in²
  2. Calculate 40% of conduit interior area: 0.304 × 0.40 = 0.1216 in²
  3. Compare: 0.0399 in² ≤ 0.1216 in²
Answer: The total conductor area of 0.0399 in² is well within the 40% limit of 0.1216 in². The fill is acceptable.
4. Three-bend saddle spacing: An obstacle on your conduit run is 3 inches tall (measured from the conduit to the top of the obstacle). Using the standard multiplier, the distance from the center-bend mark to each outer-bend mark equals the obstacle height multiplied by 2.5. What is the spacing between the center mark and each outer mark?
  1. Identify obstacle height: 3 inches
  2. Apply multiplier: 3 × 2.5 = 7.5 inches
  3. Mark the center of the obstacle on the conduit
  4. Measure 7.5 inches on each side of the center mark for the two outer 22½° bend marks
Answer: Each outer bend mark is placed 7.5 inches from the center mark (one on each side). The center bend is 45°; each outer bend is 22½°.

The math in this lesson2

Learners compute box fill in cubic inches, offset shrink at 30°, conduit percent fill, and saddle mark spacing.
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Brush up in the math halls at newSchoolWorks.com:
In class: Following their approved conduit-routing plan, students lay out box locations on the stud-wall mockup using chalk line, level, and tape measure; they install all metallic outlet, switch, and junction boxes at NEC-required heights and secure them to studs, then verify support spacing and box-fill calculations before calling for instructor sign-off on the rough-in layout. · Students hand-bend EMT conduit using a hand bender (1/2-inch and 3/4-inch), fabricating each bend type required by their design—stub-up, back-to-back, offset, and three-bend saddle—recording arrow, reference, and gain marks on a bend log sheet; the instructor measures every finished bend with a conduit level and tape, and any bend outside tolerance must be re-fabricated before installation. · Students pull NM cable and THWN conductors through installed conduit, terminate conductors at boxes using correct stripping length and approved connectors, verify conductor color-coding, and install covers; the group then performs a continuity check and megger insulation test on each circuit, logging resistance readings on the project test-record form.
Materials: EMT conduit (1/2-inch and 3/4-inch), rigid conduit sections, hand benders, conduit level, tape measure, chalk line, torpedo level, cable staples, NM cable, THWN conductors (12 AWG and 10 AWG), wire strippers, fish tape, conduit reamer, metallic device and junction boxes, box connectors and locknuts, megohmmeter, continuity tester, PPE (safety glasses, work gloves, hard hat), NCCER Electrical Level 2 module, NEC codebook
Check: Instructor uses a pass/fail field inspection checklist (modeled on a municipal rough-in inspection): all boxes at correct height (±1/4 inch), conduit support spacing within NEC limits, conduit fill within allowed percentage, all conductors color-coded correctly, continuity confirmed on every circuit, insulation resistance ≥1 MΩ. Students must pass all checklist items; any failure item must be corrected and re-inspected before proceeding.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

NCCER Electrical – Conduit Bending
1. When using a hand bender to make a stub-up, which mark on the bender is placed at the desired height line on the conduit?
NCCER Electrical – Conductor Installation and Termination
2. The NEC limits conduit fill to what percentage of the interior cross-sectional area when three or more conductors are installed?
NCCER Electrical – Box Selection and Calculations
3. During a box-fill calculation, all equipment grounding conductors entering a box together are counted as how many conductor equivalents for volume purposes?
NCCER Electrical – Circuit Testing and Troubleshooting
4. A megohmmeter reading of 0.5 MΩ on an installed circuit's insulation resistance test indicates which of the following?
NCCER Electrical – Conduit Bending
5. Which bend sequence correctly describes a three-bend saddle?
NCCER Electrical – Raceway Installation
6. Before installing conduit on a wall, the NEC requires support within a certain distance of every box or fitting. Which of the following best describes why this rule exists?
OSHA 10 – Electrical Safety / NCCER Electrical – Raceway Installation
7. A student cuts 1/2-inch EMT with a hacksaw and immediately begins to pull THWN wire through the conduit. What safety and code violation has occurred?
NCCER Electrical – Conduit Bending
8. A student measures the finished stub height of a 90° bend and finds it is 1/2 inch short of the specified dimension. According to lab policy, what must happen next?
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