Cable tray clash detection in Revit — and thinking through the detour straight away

Cable tray clash detection in Revit: real geometry checks against structure, ductwork and plumbing, with the hit shown in 3D.

Clashes that only surface on site

The tray runs along the corridor, the duct crosses it, the downstand beam comes lower than expected. On the plan that looks harmless, because two components drawn at different heights look the same as two that pass through each other. It gets noticed when the fitter is standing in front of the duct with the tray in his hands.

The damage is rarely the tray. The damage is the day on which nobody can carry on, and the change that then happens under time pressure — usually a detour that nobody documents afterwards.

On top of that, electrical design is structurally at a disadvantage here. Structure and ductwork are fixed earlier and move less; the tray is the trade that adapts at the end. Check only once everybody else has finished and you are checking a model in which you are the only one who can still get out of the way.

How checking is done today

There is Revit's own interference check, and there is coordination in the project's review tool. Both work, but in daily use they have two hurdles. The check runs across the whole model and returns lists with hundreds of hits, in which the relevant ones drown. And it finds the conflict but says nothing about what happens next.

The second route is looking at it in 3D. That is reliable as long as somebody looks, and it is the way of working most likely to be skipped when a deadline is close.

What the module takes over

Kollision prüfen works with real geometric intersections: it looks for cable trays and pipes passing through other trades — structure, walls, slabs, ductwork, plumbing. What is checked is the actual solid, not a bounding box.

The difference in daily use lies in what happens after a hit. From the result list you jump straight into a 3D view — if there is no suitable one, an isometric is created — the components involved are highlighted and the view zooms to them. You see the conflict instead of reading an element ID and going looking for it.

Then there is the command 45°-Sprung (auto). At a clash it builds a detour into the straight tray segment: diagonally up at 45 degrees, horizontally over the obstacle, diagonally back onto the original run. The jump height works in five-centimetre steps.

This command comes with a clear warning, and it is stated in the tool itself: the 45° jump is marked experimental and is to be used on a copy of the model only. It changes geometry, and that belongs checked before it goes into an issued set. If you would rather not, use the check alone — it changes nothing in the model.

When to check, and how often

A clash check at the end of design is a damage report. Its value lies in running it early and often: after every new issue of the architectural or structural model, and before the trays in your own model are detailed. At that point a detour costs one change to a run; two weeks later it costs coordination with three trades.

In practice that means applying the check to a manageable area — one storey, one construction section — rather than to everything at once. A list of twelve hits gets worked through. A list of four hundred gets put aside, and that is the real reason clash checks happen less often than everyone involved believes.

Because the check changes nothing in the model it can run at any time. It also does as a last look before issue, when there is no time for more.

What the 45° jump is and what it is not

The automatic detour answers a recurring set of clicks: split the tray, place two bends, insert the intermediate piece, align the heights. It is not demanding work, but it costs a few minutes every time, and it repeats often enough in one storey to add up to an hour.

The command builds the jump into a straight segment: up, across the obstacle, back down. The height grows in five-centimetre steps until the obstacle is clear. What it cannot do is judge whether the detour makes sense at that point. Sometimes the right answer is to pass under the duct rather than over it, to shift the run earlier, or to ask the other trade to move a hand's breadth.

Hence the warning the tool gives itself: experimental, copy of the model only. The jump is a proposal that saves you the drawing — not a decision you take into an issued set unchecked.

What a standards reference would not do here

No standard is named for this module in the shop, and there is a reason. A clash check is not a compliance check. Whether a clearance is sufficient, whether a penetration is permitted, whether a fire seal becomes necessary — that follows from the project, from the fire safety concept and from the structural engineer's requirements, not from a geometric test.

What the tool delivers is the groundwork: it shows where two components claim the same space, and takes you there. What follows from that stays with the designer.

The benefit therefore lies less in the individual hit than in the regularity. Check after every foreign issue and you collect a series of small corrections across a project that cost nothing individually. Check once at the end and you collect the same conflicts in one batch, at a point where every change pulls a coordination round behind it.

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