Can you splice in an LB?

Only if the LB is durably marked by the manufacturer with its cubic inch volume and the conductor fill calculated per NEC 314.16(B) fits within that volume.

How big does a conduit body have to be with no splices?

For 6 AWG and smaller with no splices, NEC 314.16(C)(1) requires a cross sectional area not less than twice the cross sectional area of the largest attached raceway. Conductors 4 AWG and larger send you to 314.28.

Does a conduit body have to stay accessible?

Yes. NEC 314.29 requires conduit bodies to be installed so the conductors inside can be accessed without removing part of the building or excavating.

Can I use a conduit body as a junction box?

Yes, with conditions. Section 314.16(C)(2) permits conduit bodies to contain splices, taps, or devices, provided they are durably and legibly marked by the manufacturer with their volume, the maximum number of conductors is limited by the box fill calculation in 314.16(B), and the conduit body is supported in a rigid and secure manner.

The marked volume is the gate

If the LB, LL, LR, T, or C body is not stamped with a cubic inch volume, you cannot legally splice in it. Many standard aluminum and iron bodies are not marked, which is why the answer in the field is often no. Mogul style bodies and the larger PVC bodies are commonly marked. Look on the body casting or the cover before you plan the splice.

Once you have a marked volume, run the fill calculation the same way you would for a box. Each conductor passing through or terminating counts as one at the volume in Table 314.16(B)(1). All equipment grounding conductors together count as one. A cable clamp inside counts as one. A device yoke counts as two. Then compare the total to the marked volume.

Bodies without splices still have a size rule

Section 314.16(C)(1) covers conduit bodies with no splices, taps, or devices. Where a conduit body contains conductors 4 AWG or larger, it must comply with 314.28, which is the pull and junction box sizing rule. Where it contains conductors 6 AWG and smaller, the cross sectional area must be not less than twice the cross sectional area of the largest conduit or tubing to which it is attached.

Section 314.28(A)(2) is the one that catches angle pulls. For an angle or U pull, the distance between each raceway entry inside the box and the opposite wall must be at least six times the trade diameter of the largest raceway, plus the sum of the diameters of the other raceways on the same wall and row. There is an exception in 314.28(A)(2) for conduit bodies that are marked with the maximum conductor size and used with conductors not larger than that marking, which is how a properly marked mogul LB legally takes 3/0 conductors that a strict six times calculation would prohibit.

Support and access

Section 314.23 requires the body to be rigidly and securely fastened in place. A conduit body supported only by two threaded rigid conduits is permitted under 314.23(E) and 314.23(F) when the conduits are threaded wrenchtight into the body and each conduit is supported within 900 mm, or 3 feet, of the body, or within 450 mm, or 18 inches, for a body that has no devices.

Section 314.29 requires the body to remain accessible without removing any part of the building or, in underground work, without excavating sidewalks, paving, or earth. An LB buried in a soffit that gets drywalled over is a violation whether it has splices in it or not.

Field takeaway

Check for a stamped cubic inch volume. If it is there, calculate fill per 314.16(B) and splice away. If it is not, the body is a pulling fitting only. Either way, keep it accessible and supported per 314.23.