How to Install an Electrical Pull Box: Step-by-Step

> **Quick Answer:** Installing a pull box correctly means sizing it per NEC 314.28 first, selecting the right NEMA rating for the environment, mounting it securely, seating conduits with proper locknuts and bonding bushings, pulling conductors without exceeding tension limits, and labeling it before the inspector shows up.

Tools and Materials You'll Need

Before you start, get everything on the truck. Missing a knockout punch in the middle of a pull wastes time.

**Tools:**

- Knockout punch set (½" through 4" minimum; Greenlee or Ideal are standard)

- Hydraulic knockout driver for 2½" and larger

- Conduit benders (½" through 2" hand benders; hydraulic bender for 2½"+)

- Fish tape or wire mule for conductors

- Cable pulling lubricant (pulling compound, not WD-40)

- Torque wrench or calibrated ratchet (for bonding bushing screws)

- Level and tape measure

- Unistrut cutter and punch driver

- Drill with carbide bits for concrete or steel

**Materials:**

- Pull box (sized per NEC 314.28 — see Step 1)

- Conduit locknuts — two per conduit entry: one inside, one outside

- Grounding/bonding bushings (Bridgeport or equivalent) for each conduit

- Thread sealant for RMC threaded entries (Rectorseal or similar)

- Unistrut channel, beam clamps, or wall brackets for mounting

- ½" or ⅜" threaded rod and hanger rod couplings (for suspended mounting)

- #10 bonding jumper wire and lugs if required by AHJ

- Metallic conduit nipples or hubs for each entry point

- Label maker tape or permanent marker for circuit identification

Step 1: Size the Box Using NEC 314.28

Don't order the box until you've run the calculation. This is the step most people skip, and it's how pull boxes get red-tagged.

For a **straight pull** (conductors enter one wall and exit the opposite wall in a straight line), the formula is:

**Box length ≥ 8 × trade size of the largest conduit**

For an **angle pull** (conductors change direction inside the box), the formula for each wall is:

**Box dimension ≥ (6 × largest conduit on that wall) + (sum of remaining conduits on the same wall)**

Apply the angle pull formula independently for each wall that has conduits entering it.

**Example:** Three conduits entering the left wall (2", 1½", 1") making 90° turns to exit the bottom wall.

- Left wall to right wall: (6 × 2) + 1.5 + 1 = 14.5" → round up to 16"

- Bottom wall to top wall: same conduits, same calculation = 14.5" → round up to 16"

Order a 16×16×6 minimum. Use the [NEC 314.28 pull box sizing calculator](/pull-box-sizing-calculator) to verify your numbers before calling the supply house.

Also check: if you're making splices in the box, you need enough interior volume for the splice connectors. A 16×16×6 gives you 1,536 cubic inches — more than enough for most applications — but for very large conductor splices (350 kcmil+), confirm the connectors physically fit.

Step 2: Select the Right NEMA Rating

The NEMA rating determines what environment the box can handle. Don't overspend on stainless in a dry indoor location, and don't put a NEMA 1 box outside.

**NEMA 1 (general purpose, indoor):** Dry, conditioned spaces. Electrical rooms, office spaces, commercial interiors. Steel, painted or galvanized. This covers most commercial interior pull boxes.

**NEMA 3R (rainproof, outdoor):** Covered outdoor locations, rooftops, equipment yards. Protects against falling rain and sleet. Not rated for hosedown or submersion.

**NEMA 4 (watertight, indoor/outdoor):** Outdoor exposed locations, washdown areas, areas with water spray. Common on processing lines and exterior equipment.

**NEMA 4X (corrosion resistant):** Food processing facilities, chemical plants, coastal locations. Usually 304 or 316 stainless steel, or fiberglass. Costs significantly more than NEMA 4 steel.

**NEMA 12 (industrial, dust and drip tight):** Factory floors, non-hazardous indoor industrial environments. Protects against dust, lint, and dripping non-corrosive liquids.

If the area has a hazardous classification (Class I, II, or III, Division 1 or 2), you're not selecting from this list — you need explosion-proof or dust-ignitionproof enclosures listed for the specific classification. That's a different process entirely.

Step 3: Mount the Box

Pull boxes need solid, permanent mounting. Conductors will exert tension on the box during pulls, and a poorly mounted box can shift or separate from the conduit system.

**Wall mounting:** For boxes 12×12 and smaller, direct wall mounting with 3/8" or ½" lag bolts into studs or masonry anchors is typical. Use a minimum of 4 fasteners — one per corner — and torque to the manufacturer spec. For masonry, use sleeve anchors or wedge anchors, not toggle bolts.

**Unistrut (Superstrut) mounting:** For larger boxes or where wall penetrations aren't practical, mount to Unistrut channel. Two horizontal channels, top and bottom, with beam clamps to the structure. The box attaches to the strut with strut nuts and bolts at all four corners. This is common in industrial settings and electrical rooms with cable tray or overhead structure.

**Hanger rod suspension:** For pull boxes hanging from concrete ceilings or structural steel, use 3/8" or ½" all-thread rod with beam clamps, concrete inserts, or Hilti anchors at the top. Two rods minimum for any box heavier than about 20 lbs. Secure the box to the rods with strut channels and trapeze hardware.

Check level in both directions before tightening anything permanently. Conduit alignments are much harder to correct after the box is mounted.

Step 4: Knock Out the Conduit Entries

Lay out your conduit entry locations before punching. This is worth taking 10 minutes to plan.

Mark the center of each knockout with a punch or marker. Leave at least 1" of steel between knockout edges — closer than that and the box wall starts to lose structural integrity. For large conduits (3" and up), you may be limited to two or three entries per wall even on a 24" box.

Use the right punch for the conduit type. Conduit knockouts are sized for the conduit OD plus the locknut — not the trade size. A 2" trade size knockout is typically 2.423" — check the punch manufacturer's spec for exact dimensions.

Don't punch more knockouts than you'll use. Unused open knockouts are a code violation (NEC 110.12 requires electrical equipment to be installed without open holes). Cover unused knockouts with listed closure plugs.

For threaded RMC entries, punch the knockout and use a threaded hub or chase nipple rather than running the conduit directly through a bare knockout with locknuts. Threaded entries are more secure and better for weatherproof applications.

Step 5: Secure Conduit to the Box

This step is where bonding and grounding requirements apply. Don't skip the bonding bushings.

For **EMT and IMC**, use two locknuts per entry — one inside, one outside. Tighten until the teeth of the locknut bite into the metal of the box. The conduit connector or coupling on the outside should be tight against the box wall.

For **RMC**, thread the conduit until it's hand-tight, then apply a grounding/bonding bushing on the inside. The bonding bushing has a set screw that bonds the conduit to the box and ensures a continuous ground path. Apply thread sealant (Rectorseal or equivalent) on the threads before final tightening — this is required for wet locations and good practice everywhere.

For service entrance conductors and feeders larger than 250 kcmil, NEC 250.102 may require an equipment bonding jumper at the pull box. Check the specifics for your installation — a #2 AWG or larger bonding jumper from the conduit system to the box ground lug is common on service gear.

Conduit must be supported within 3 feet of the box entry per NEC 344.30 (RMC), 358.30 (EMT), or the applicable conduit article. Don't let conduit runs hang unsupported right up to the box — the AHJ will catch it.

Step 6: Pull the Conductors

Large conductors don't pull like branch circuit wire. They need lubrication and controlled tension to avoid insulation damage.

**Apply pulling compound:** Use a wire and cable lubricant designed for the conductor insulation type. THHN/THWN conductors are compatible with most wire-pulling compounds (Ideal Yellow 77, Gardner Bender Lube-It Extra, etc.). Don't use petroleum-based lubricants on PVC insulation — they can cause swelling and insulation degradation over time.

**Don't exceed the maximum pulling tension.** Per NEC 300.17 (informational note) and conductor manufacturer specs, pulling tension for copper THHN is typically limited to 0.008 × circular mil area of the conductor in pounds. For a 4/0 AWG conductor (211,600 CM), that's about 1,693 lbs. Exceeding this damages the conductor, even if the insulation looks fine externally.

For large pulls through multiple conduits or long runs, use a mechanical or motorized wire puller with a built-in tension limiter. Mark the conductors at the pull box location before pulling begins so you know where each one ends up.

**Inside the pull box:** As conductors emerge, guide them without kinking. Large conductors have minimum bending radii — for 500 kcmil THHN, that's typically 7× the conductor diameter. Don't fold them over a sharp edge or force them into a sharp bend inside the box. The whole point of sizing the box correctly with NEC 314.28 is to give the conductors room to make the required bend without damage.

Leave enough slack inside the box for future work. 12" of slack on each conductor going forward is a reasonable standard; more on service conductors where future reconnection is expected.

Step 7: Label the Box and Close It Up

NEC 110.22 requires that each disconnect, overcurrent device, and similar equipment be legibly marked to indicate its purpose. Pull boxes don't require circuit directory labels in the same way as panelboards, but clear identification of the circuit or feeder inside is best practice — and some AHJs require it.

At minimum, mark the box with:

- Circuit or feeder designation (e.g., "MDP-A to Panel 3B, 400A 480/277V")

- Voltage and phase if not obvious

- Any warning required by the NEC (e.g., "Caution: Multiple Sources" if applicable)

Close the box with all cover bolts torqued. NEMA 4 and 4X boxes use neoprene or silicone gaskets — make sure the gasket is seated properly and not pinched before tightening. Tighten bolts in a crossing pattern, not in a circle, to compress the gasket evenly.

AHJ Inspection Checklist

When the inspector shows up, here's what they're checking:

- **Box size:** Does it meet NEC 314.28 for the conduit configuration? Be ready to show your calculation.

- **Mounting:** Is the box securely fastened? No movement when pushed?

- **Conduit entries:** Are locknuts and bushings properly installed? No unused open knockouts?

- **Bonding:** Are bonding bushings installed? Is there continuity from conduit to box?

- **Conductor condition:** No visible insulation damage, no conductors pinched by cover or fittings?

- **Cover:** Fully closed, gasket intact (for outdoor/wet rated boxes)?

- **Labeling:** Circuit identified, voltage marked?

- **Conduit support:** Conduit supported within required distance of box entry?

Running through this list before calling for inspection saves a re-inspection fee. For information on choosing the right NEMA rating for your installation environment, see [NEMA pull box ratings explained](/nema-pull-box-standards). And if you're still working out the box size, the [pull box dimension calculator](/pull-box-sizing-calculator) has you covered.

Check out the [about page](/about) for more on how our sizing methodology is built and verified against NEC requirements.