Thomas & Betts XD8-TB 3 INCH EXP/DEFL COUPLING

The XD8-TB is the 3 inch size in the XD expansion/deflection coupling line, so it goes on 3 inch trade size conduit runs. Order the matching size for the raceway you are joining; a 3 inch coupling will not adapt a smaller or larger run.

A plain expansion coupling only takes up movement along the length of the conduit, as the run grows and shrinks with temperature. An expansion/deflection fitting such as the 3 inch XD8-TB handles length change plus angular and side-to-side deflection, which is what you want at a building seismic or settlement joint, between structures, or where a run crosses from a slab to a wall that can move independently. If the only movement is thermal along a straight run, a straight expansion fitting is the simpler choice.

That is exactly the application for a 3 inch XD expansion/deflection coupling like the XD8-TB. It is installed in the run where it crosses the joint, and it absorbs both the length change and the relative movement of the two structures instead of transferring that load into the conduit, straps, and boxes. Size the fitting to the conduit trade size, and use one at each joint the raceway crosses.

Ductile cast iron. That is the material to specify where the fitting is exposed to mechanical abuse, in a garage or industrial space, or buried in structure at a movement joint. Ductile iron takes impact and bending load better than gray iron, and it is why these fittings get used on larger feeder conduit like 3 inch rather than a sheet metal body.

One part. XD8-TB is the complete manufacturer part number for the 3 inch Thomas and Betts expansion/deflection coupling, with no finish or configuration choices to specify. Quote it by that number and the size is already fixed at 3 inch.