Track sections and isolation: why and how
Benjamin | TrackDrawer.com · published 13 November 2026
A track section is a length of track that is electrically separated from the rest and gets its own feed or its own detector. You need sections to hold a loco on analogue, to make a reversing loop work on two-rail, to know where a train is, and to split a large layout over several boosters. On two-rail you isolate with insulated rail joiners in one rail or in both; on Märklin three-rail you usually just break the centre conductor.
Why you divide a layout
On a layout without gaps, all the track is one electrical whole. That is simple, but it limits what you can do. There are five reasons to isolate a section, and each one calls for a different kind of break.
| What for | Two-rail | Märklin three-rail |
|---|---|---|
| Holding a loco on analogue | gap one rail, feed the section through a switch | break the centre conductor |
| Reversing loop | gap both rails, at both ends | not needed |
| Occupancy detection | gap one rail, feed the section through a current detector | isolate one outer rail (contact track) |
| Stop section at a signal | gap one rail | break the centre conductor |
| Boundary between command station and booster, or between two boosters | as the booster's manual specifies | as the booster's manual specifies |
A sixth case belongs to the turnouts: behind a live frog you gap both rails on two-rail, because the frog changes polarity. That is explained in loco stalls on the frog.
One rail or both
On two-rail the rule is simple. If you only want to switch a section off or monitor it, one rail is enough: the other rail stays continuous and is common to all sections. If the polarity of a section flips, as in a reversing loop or behind a live frog, you have to gap both rails. Gap only one, and the second rail still makes the short. Why a reversing loop causes a short circuit is covered in the reversing loop.
On Märklin three-rail both outer rails are the return and always run through. Track power is in the centre conductor, and that is what you break for a switchable or separately fed section. For a contact track you isolate one outer rail instead, so that a wheelset triggers the report.
How each system isolates
Most systems isolate with insulated rail joiners: plastic joiners that connect the pieces mechanically but not electrically. Some systems also have a dedicated piece. In our catalogue:
| System | What the catalogue has |
|---|---|
| Märklin C track | 74030 centre conductor insulators (10 pieces); 24995 contact track with an isolated outer rail |
| Märklin Z | 8588 isolating track, 55 mm |
| Hornby | R618 isolating track, 168 mm |
| Arnold N | HN8027 isolated track, one side, 111 mm |
| Kato Unitrack N and H0 | no dedicated piece; isolate with insulated joiners |
An isolating track has the same shape as an ordinary straight, so in your plan you lay it in place of a straight of the same length. A loose insulated joiner takes up no length.
Where the gaps go
- At turnouts. Turnouts are the natural boundaries. A section runs from turnout to turnout, or from a turnout to a buffer stop.
- Longer than the longest train. A train standing across a gap bridges it with its wheels or with lit coaches. A holding siding or a reversing loop must therefore hold the whole train. A worked example: a loco with four wagons in H0, using the 250 mm standard wagon TrackDrawer works with, is 5 x 250 = 1250 mm long. A block for that train is at least as long, plus the braking distance.
- A short stop section. At a signal a piece slightly longer than your longest loco is enough. The rest of the block stays powered, so only the loco goes dead and the wagons behind it stay put.
- Opposite each other. If you gap both rails, put the two gaps directly opposite each other. That way no wheelset has one wheel in one section and the other wheel in the next.
Section and block
On a real railway a block is a stretch of line in which only one train may run at a time. Signals at the start of each block guard that: that is block signalling. On a model railway you borrow the idea to let trains run on their own. Electrically a block is then often one or two sections: a length with an occupancy detector and, at the end, a stop section at the signal.
On analogue a block means the signal cuts the power in the stop section. On digital there is power everywhere: the block is then a length with a detector, and the command station or a computer program decides that the loco stops. How detectors work is covered in feedback: knowing where your train is. Which gaps remain on digital is also covered in analogue or digital control.
Label and draw
A layout with sections soon has dozens of wires. Give every section a name or number, write it on the feeder under the baseboard and keep a drawing. Anyone tracking down a fault later saves hours that way. Every separately fed section also needs its own feeder: a section without power is a section where nothing runs.
Frequently asked questions
Do I need to divide a digital layout into sections as well?
Less than on analogue, but usually a little. Holding trains works on digital without gaps, because every loco stops on its own address. You still need gaps for a reversing loop on two-rail, for occupancy detection and at the boundary between command station and booster.
Can I add a gap later?
Yes, but under ballast and scenery it is awkward. Replacing a joiner with an insulated one means lifting the track. Plan the gaps before you ballast, even if you do not use them yet: a gap that you bridge with a wire link can be opened again later with a single cut.
Sections in TrackDrawer
TrackDrawer derives the blocks of your plan from turnouts and signals. Every signal closes a block, turnouts and crossings are boundaries, and the contact tracks in a block are its detectors. In the digital panel (Pro) you see for each block the number of pieces, the length in metres, the number of detectors and the number of signals, so you can see at once whether your longest train fits. If you place a signal with a stop section on C track, TrackDrawer counts two 74030 centre conductor insulators for that section. The blocks go into the Rocrail export with their lengths.
On two-rail the check also follows the left rail through your whole plan. If the polarity flips anywhere, you get a message naming the two pieces between which you have to gap both rails.
Lay out your track in the app, place your signals and see which blocks TrackDrawer derives from them.
