Conduit Body: The Types, the Volume, and the Splice Rule

What is a conduit body?

A conduit body is a fitting that opens a raceway. NEC Article 100 defines it as a separate portion of a conduit or tubing system that provides access through a removable cover to the interior, at a junction of two or more sections or at a terminal point. It is part of the pipe, not a box on it.

SimplyWise Cost Estimator turns a photo of the work into an itemized estimate in about 6 seconds.

Why it is not a box

The same definition adds that FS and FD boxes, and larger cast and sheet metal boxes, are not conduit bodies. An outlet box mounts to structure and holds a device. A junction box holds splices. A conduit body does either only when it is built and marked for it.

What Article 314 actually requires

Three rules govern. The splice rule is the one crews get wrong.

Splices: 314.16(C)(2) is conditional

Only conduit bodies the manufacturer durably and legibly marked with their cubic inch capacity may contain splices, taps or devices. The count is then figured the same way as fill in any other nonstandard box. No marking, no splice.

Pass through: 314.16(C)(1) sizes the body against the pipe

Any conduit body enclosing 6 AWG or smaller, other than a short radius type, needs a cross sectional area at least twice that of the largest conduit it attaches to, splices included. With no splice, the count is whatever that conduit may carry. Short radius bodies, capped elbows and service entrance elbows get 314.16(C)(3). No splices, taps or devices.

Pulling room: 314.28 starts at 4 AWG

At 4 AWG and larger insulated conductors the dimensional rules switch on. A straight pull needs a body at least eight times the trade size of the largest raceway. An angle pull, a U pull or a splice needs six times that from each entry to the opposite wall, unless that wall is the removable cover. Add the diameters of the other entries in that row. Under 314.28(A)(3) a listed body may be smaller.

A worked example, 12 AWG in a 3/4 inch LB

Table 314.16(B)(1) gives 12 AWG a volume allowance of 2.25 cubic inches each.

• Splice a two wire circuit: hot in, hot out, neutral in, neutral out. 4 x 2.25 = 9.00.
• The grounds together take one allowance, another 2.25. Total 11.25 cubic inches.
• Southwire Form 7 Type LB, 3/4 inch, part LB2G7: internal volume 5.8. No.
• Appleton Form 85 Type LB, 3/4 inch: 7.00 body plus a 0.80 cover, so 7.80. No.
• Step to 1 inch. Southwire LB3G7 is 9, still short. Appleton Form 85 is 11.80 body plus a 0.50 cast cover, so 12.30.

The letters, in plain language

LB, LL, LR, C, T and X is the common set. IAEI describes the two hub bodies as straight, LB, LL or LR, three hub bodies as T and four hub bodies as X. The second letter marks where the run is diverted, not where the cover sits.

Where it shows up on a job

On the takeoff

Count bodies per corner and pull point. Our electrical estimate template keeps them off the fittings lump.

At inspection

The inspector looks for the volume marking first.

Common mistakes

Splicing in an unmarked body

The marking is the permission. Plenty of listed bodies carry no capacity marking, because they were never meant to hold a splice.

Sizing off the hub

Hub size and internal volume do not track across makers.

Pick a conduit body in four steps

1. Decide whether anything gets spliced

   No splice, tap or device means 314.16(C)(1) governs and the pipe sets the count.

2. Read the cubic inch marking

   If you are splicing and there is no legible manufacturer capacity on the casting, the body is out.

3. Add the box fill

   Count each conductor once at its Table 314.16(B)(1) allowance, one allowance for four grounds or fewer, a quarter each beyond.

4. Check 314.28 if anything is 4 AWG or larger

   Eight times the trade size for a straight pull, six for an angle pull, unless listed smaller.