Making a cable tray tee branch by hand
When a branch has to come off a main run and there is no factory tee to hand, the junction is made from plain tray. It comes out strong and tidy, and above all with no sharp edges in the cable path. All it takes is a grinder or snips, a spanner and a tape.
What it looks like finished
The branch sits into an opening cut in the side of the main run. The sides of the branch are cut and two tabs are folded out of them, one each side. The tabs tuck <b>inside</b> the main tray, wrapping round the edge of the opening, and pull up against the side on M6 bolts from within. The base of the branch is not cut at all and runs in under the base of the main tray.
Why the tabs go inside, not outside
The reason is the cable, not the strength. Once the side of the main tray is cut it is left with a sharp edge, and a tab tucked inside covers it. The base of the branch goes under the main base for the same reason: otherwise the cut end of the base lies right in the cable path and the insulation gets damaged when the run is pulled in. The whole junction is built around one principle — no cable should ever touch cut metal.
Tab sizes
Tabs are made about 100 mm long. It comes down to the perforations: over that length there is almost always a row of ready-made holes, so nothing needs drilling — the bolt goes through the factory perforation in both trays. On top of the tab comes the swept section, another 50 to 100 mm: it splays the tabs out and gives a smooth turn instead of a hard corner.
Width of the opening
The opening is wider than the branch itself, by the reach of the tabs on both sides — otherwise the splayed tabs will not go in. A swept section turned through 45 degrees moves the edge sideways by about 0.7 of its length. So: branch width plus one and a half times the swept section. For a 200 mm branch with a 70 mm sweep that is around 300 mm, or 50 mm each side.
Marking in place beats calculating
The formula above is for sizing the job up in advance and checking the junction will fit where you want it. The final opening is drawn round the finished branch, and that is not a shortcut but the more accurate way. The fold radius depends on metal thickness, on the tool and on how the edge came over: a few millimetres out and the tab no longer seats. A finished part allows for all of it, which is why the order is branch first, marker second.
When a fitting is the better buy
If all three ways are the same width, a factory tee goes in faster and looks neater. Where the branch steps down to a smaller width, reducing tees are made for it. A hand-made branch wins where the fitting is not on site and the run has to be finished today, or where the sizes are non-standard.
Order of work
- Mark the tabs on the branch: about 100 mm, plus 50–100 mm for the sweep.
- Cut along the base of the side — where the side meets the base, from the first fold line to the end. The freed strip becomes the tab. Do not cut the base itself.
- Fold the tabs on both lines: 45° for the sweep, then 45° to sit against the side.
- Hold the finished branch up to the main run and mark round it to get the opening.
- Cut the opening in the side of the main tray.
- Straighten the tabs out — the branch will not go in otherwise.
- Run the base of the branch in under the base of the main tray.
- Fold the tabs back on the same lines, in place, tucking them inside the main tray.
- Pull it up with M6 bolts through the matching perforations.