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Fittings & materials index

The stuff you get handed and are expected to already know the name of. Each one is drawn from scratch here, with a plain sentence on what it does. It is a naming reference, not a spec — the sizes, ratings and where each is permitted live in the manufacturer's data and the code.

  • ConnectorTies a length of raceway into a box; here a set-screw type that grips the tube and threads into the enclosure.
  • CouplingJoins two lengths of raceway end to end in a straight run.
  • One-hole strapFastens a single run of pipe to a surface with one screw.
  • Two-hole strapA flatter strap held by two screws, one each side of the pipe.
  • LB body (condulet)A cast fitting that turns a rigid run through a right angle with a removable cover for pulling.
  • Device boxHolds a switch or receptacle and its terminations, with knockouts for the raceway.
  • BushingThreads onto a raceway end to give conductors a smooth, protected edge to pass over.
  • LocknutA toothed nut that bites into the enclosure to lock a connector or fitting tight.
  • Twist-on connectorA cap with a spring inside that joins stranded or solid conductors by twisting on.
  • Strut channelA C-shaped metal channel that mounts to structure and carries straps, clamps and supports.
  • Beam clampGrips the flange of structural steel so a hanger or rod can hang without drilling.
  • Reducing washerA stepped washer set that closes down an oversized knockout to fit a smaller fitting.
  • Set-screw couplingJoins two lengths of thin-wall tube with a screw that bites each end. Dry locations — the screw is the grip, nothing seals it.
  • Compression couplingA nut each end squeezes a ring onto the tube. The seal is what makes it the one for damp or outdoor runs — read the listing on the box.
  • Cable connector (NM clamp)Grips a sheathed cable where it enters a box so a tug outside cannot pull on the splices inside. A screw-down clamp or a snap-in.
  • Box extension ringA collar that brings a buried box out flush with the finished wall, or adds room to a box that ran out of it.
  • Grounding bushingA bushing with a lug on it, so the bonding conductor can land right at the raceway end where the metal path might otherwise be interrupted.
  • Threaded rod and hangerAll-thread dropped from the structure with a trapeze or a ring hanger on the end — the way a run is carried across a ceiling.
  • Conduit hanger (clip)A one-piece strap with a bolt hole that hangs a single run from a rod, a beam clamp or a strut nut.
  • Expansion fittingA sliding joint that lets a long run grow and shrink with the temperature without pulling apart or buckling. Long PVC runs and building joints.

Which fitting, where

A fitting is matched to two things: the raceway it goes on and the place it lives. The first is obvious — a thin-wall connector will not thread onto rigid, a PVC coupling is glued not screwed. The second is the one that catches people. Every fitting is listed for certain conditions, and the words on the box are the words to read: dry locations, wet locations, rain-tight, concrete-tight, indoor, outdoor. A set-screw fitting that is fine in a ceiling space is the wrong part on the outside of the building; a compression fitting is the same shape and passes. Which fitting is permitted where is the listing's job and the code's — read both before you buy a box of the wrong ones.

What the inspector looks at on a fitting

  • Set screws actually tightened — a connector that slides on the tube is not a connector.
  • Locknuts bitten into the enclosure, inside and out where the fitting calls for both, so the metal is held and the path through it is solid.
  • A bushing on every raceway end that conductors pass over, so the insulation is not sitting on a sharp edge.
  • The bond continued through every fitting where the metal raceway is the bonding path — including the reducing washers and the eccentric knockouts that interrupt it, which is where a grounding bushing earns its lug.
  • Straps and supports at the intervals and distances the book gives for that raceway, and a strap on each side of a box or fitting where it asks for one.
  • No fitting doing a job it is not listed for — an indoor fitting outdoors, a dry-location coupling in a slab, a clamp meant for one cable holding two.

Some of these get their own glossary entry — the LB and C bodies, for one. The glossary explains the words; this page shows the things.

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