Plan an Overdrive run on DMX-rated 120 ohm shielded twisted pair, up to roughly 150 m (about 500 ft), with no more than 32 receivers, spurs under half a metre (about 18 in), a 120 ohm terminator at the far end, and no standard-speed devices sharing the line. Every figure below is an approximation for planning, not a specification, and has to be confirmed against the actual project before a design is committed.
| Item | Overdrive planning figure | Standard DMX for comparison |
|---|---|---|
| Cable | DMX-rated 120 ohm shielded twisted pair | Often gets away with much less |
| Total run length | Approximately 150 m (500 ft) | 300 m (1000 ft) commonly quoted |
| Receivers per line | Up to 32 | Up to 32, unchanged |
| Spurs and stubs | Under approximately 0.5 m (18 in) | A few metres usually tolerated |
| Termination | 120 ohm, mandatory | Frequently omitted without consequence |
| Topology | Daisy chain only | Daisy chain, with more latitude |
| Mixed speeds on one line | Not possible | Not applicable |
These are planning figures, not a specification
None of the numbers above is a specification, a limit ENTTEC warrants, or a figure you can rely on for a particular installation. What a given line will actually carry depends on the cable, the topology, and above all the fixtures on it. Treat them the way you would treat a rule of thumb from a colleague: useful for sketching, not for signing off. If you have not read what changes when DMX runs faster than the standard, start there, because it explains why these are tighter than the standard DMX equivalents.
Cable
Use DMX-rated 120 ohm shielded twisted pair from a manufacturer that publishes its cable's characteristics. In standard DMX the choice of cable is forgiving enough that many installers never think about it. In Overdrive it is a real variable, and the difference between one cable and another is much larger in proportion.
Microphone cable is not DMX cable, and the reasons it usually gets away with it at standard DMX speed do not carry over. See Can I use a microphone cable for DMX? for why it is a poor choice even at standard speed.
Structured data cable such as Cat5e is used successfully for DMX in many installations, but grades and manufacturing quality vary more than the category label suggests. If you intend to use it for Overdrive, its characteristics need confirming for the project rather than assuming.
Run length
Plan on roughly 150 m (500 ft), against the 300 m (1000 ft) usually quoted for standard DMX in How far can you run DMX cable?. The shorter figure is not because the cable stops working. It is because the faster a line runs, the less signal degradation it can absorb before the receiver's decision becomes unreliable.
One point that catches people out: the length of cable between the node and the first fixture matters in its own right, not merely as part of the total. A long leader into a dense array behaves differently from the same total length distributed evenly. If your installation has a long run before the first fixture, flag it as something to confirm rather than something to average out.
Number of receivers
Up to 32, exactly as for standard DMX. This is the one familiar number that carries over unchanged, because the limit comes from the electrical load each receiver places on the line, and that loading does not change with speed. See How many fixtures can you connect on one DMX line?.
Do not read this the other way round. Staying within 32 receivers does not make a line safe for Overdrive. It only means you have not broken the one rule that did not change.
Spurs and stubs
Keep any branch off the main run under roughly half a metre (18 in). Standard DMX tolerates a few metres and installers routinely use that latitude.
Remember what counts as a stub: a short tail from a junction into a fixture, the unused leg of a Y-splitter, a long tail coiled inside a connector box, or a drop to a socket with nothing plugged into it. These are easy to overlook because they are not on the drawing as cable runs.
Termination
Terminate the far end of every Overdrive run with 120 ohm across the two data pins. In standard DMX, termination is widely treated as optional and frequently gets away with it. In Overdrive, treat it as mandatory. See DMX termination: when the 120 ohm resistor matters for what a terminator actually does.
Topology
Daisy chain only: out of the node, into fixture one, out of fixture one, into fixture two, and so on to a terminator. No stars, no T-pieces, no Y-splitters, no passive splits of any kind. Where you need to branch, use a splitter that is rated for Overdrive.
Do not mix speeds on one line
Every receiver on an Overdrive segment must support Overdrive. A standard-speed DMX device sharing the line will not simply ignore data it cannot read. It will see continuous corrupt data and may behave unpredictably. Segments have to be homogeneous. If part of your rig needs standard DMX, give it its own output or its own segment.
Splitters and isolators are not automatically compatible
This is the requirement most likely to catch out an experienced installer, because it concerns equipment that is already installed and already working.
A DMX splitter, buffer, patch panel or optical isolator that performs perfectly at standard DMX speed may not pass Overdrive at all, or may pass it in a degraded form that works on the bench and fails intermittently on site. Optical isolation deserves particular attention: isolation is good practice and worth having, but the components used are often selected for standard DMX speeds and cannot follow a faster signal cleanly.
Do not assume existing distribution equipment passes Overdrive. Each device needs confirming. See optical isolation and DMX splitting for large-scale and outdoor installations for background on why isolation is used.
If your installation does not fit
Exceeding these figures does not necessarily mean the installation is impossible. It means the design needs to be worked out rather than assumed. The usual options are to split the run into shorter segments through a rated splitter, to distribute the load across more outputs, to run standard DMX on the parts of the rig that do not need Overdrive, or to have the design reviewed. Which of those is appropriate depends entirely on the project.
Quick checklist for an Overdrive run
- DMX-rated 120 ohm shielded twisted pair, known make and type, for the whole run.
- Around 150 m (500 ft) maximum, including the leader from the node to the first fixture.
- No more than 32 receivers on the line.
- Every spur, tail and drop under about half a metre, including the ones not on the drawing.
- One 120 ohm terminator at the far end. Not optional.
- One continuous daisy chain. No stars, Ts or Y-splitters.
- Every splitter, buffer and isolator on the line confirmed as Overdrive-rated.
- No standard-speed devices sharing an Overdrive segment.
- Every figure above confirmed against the actual project before the design is committed.
The cable is only part of it
Everything on this page is necessary and none of it is sufficient. A perfectly specified cable installation will still fail if the fixtures on it are not suitable, and the fixtures are the part almost nobody checks. See Overdrive mode: your fixtures decide whether it works.
Responsibility
Installation design is the responsibility of the system designer or installer. ENTTEC specifies the operating conditions for Overdrive mode. Verifying that a given installation meets them, including the behaviour of fixtures ENTTEC did not supply, requires a review of the specific design. Where ENTTEC supplies the node, the cable specification and the fixtures, the chain is validated as a system.