Conduit & Grounding Bushings

Where a conduit enters a box, the bare end of the raceway has to be dealt with - smoothed so it won't cut conductors, bonded so it carries fault current, or reduced to fit a smaller knockout. Bushings handle all three: an insulated bushing softens the throat, a grounding bushing adds a bonding lug, and a reducing bushing adapts the hole. Lumera Electric's range covers insulated, grounding, reducing, and anti-short bushings in plastic and metal.

Conduit & Grounding Bushings

What's the difference between an insulated, grounding, and reducing bushing?

Each bushing solves a different problem at the conduit end. An insulated bushing gives the raceway a smooth plastic throat so it won't nick conductor insulation. A grounding bushing adds a lug to bond the conduit for fault current. A reducing bushing adapts a large knockout to a smaller conduit size. Pick by the job.

What is a grounding bushing, and when is it required?

A grounding bushing is a metal bushing with a built-in lug for landing a bonding jumper or equipment ground. Code requires bonding bushings where standard locknuts can't be trusted to bond — at concentric or eccentric knockouts, and on circuits over 250 volts to ground, per NEC 250.97. The lug ties the conduit into the grounding path.

What does an insulated bushing protect against?

Metal conduit has a sharp edge at the cut end that can slice through conductor insulation as wires are pulled. An insulated bushing caps that edge with a smooth plastic or nylon throat, rated to a temperature like 150°C. The NEC requires an insulated throat on conduit carrying 4 AWG and larger conductors.

How does a reducing bushing or washer change conduit size?

It steps a large knockout down to a smaller conduit. A reducing bushing threads into an oversized hub to accept a smaller fitting. A reducing washer (used in pairs) fills the gap around a smaller connector in a big knockout. Both let you land a 1/2-inch fitting in a 3/4-inch opening cleanly, without an adapter run.

What is an anti-short bushing (red head) for?

Cut armored cable has razor-sharp edges where the metal jacket ends. An anti-short bushing — the red plastic "redhead" — slides over the conductors at that cut, shielding them from the jacket. It's required on AC (BX) cable terminations and standard practice on MC, so the steel armor can't abrade the wire. Install one at every armored-cable end.

Finishing the raceway? Connectors and couplings are in EMT Connectors & Couplings, the full fitting range sits under Conduit Fittings, and the bonding jumpers a grounding bushing lands are in Grounding & Bonding.