B-Line Eaton series imperial cable tray and ladder, 6" Height, 36" Length, 18" Width, 18" and 9" Tray widths, Series 2-5 horizontal reducing tee, Alum

Plan for a 24 inch bend radius on the branch and an overall fitting length of 36 inches. That radius is what protects large power conductors from being bent tighter than their minimum bend radius, but it means you need clear room around the intersection, plus support within the manufacturer's spacing of each fitting end.

27.3 lb for the fitting itself. Aluminum keeps it to a two-man lift at height, but add the weight to the cable fill when you size the trapeze or wall bracket at the intersection, since a tee concentrates load at one point in the run.

A reducing tee like the 6A-18-09-HT24 does both jobs in one piece: it takes the 18 inch run and turns out a 9 inch branch. Using a full width tee and then a reducer adds a second set of splice plates, more hardware, and more length to the layout. Go with the straight tee and reducer only when the width change has to happen somewhere other than at the intersection.

Order it as Eaton B-Line 6A-18-09-HT24. Reading the code: 6 inch depth, aluminum, 18 inch main width, 9 inch branch width, horizontal tee, 24 inch radius. Splice plates and hardware are separate line items on B-Line tray fittings, so confirm you have the connectors for each end.