Trackwork
How do you install a turnout and switch machine that will not short or stall?
Quick answer
A turnout's number is its geometry: it moves one unit sideways for every N units forward, so a number 6 is gentler and longer than a number 4. Electrofrog, or live frog, turnouts stop short-wheelbase locomotives stalling but must be wired correctly or they short. Insulfrog, or dead frog, turnouts are simpler to wire but can stall a short locomotive crossing the gap.
A turnout's number is the one piece of information that decides almost everything else about it. It is a rate, not a size: a number 6 turnout diverges one unit sideways for every six units of travel forward, measured at the frog, and a number 4 diverges more sharply over a shorter length. Higher numbers are gentler and better suited to longer equipment, and they cost more space to install. See the turnout geometry calculator for the exact frog angle and ladder length a given number produces in your own scale.
The other decision a turnout makes for you is frog type. Electrofrog turnouts have a frog that is electrically live, which prevents a short locomotive with few pickup wheels from stalling as it crosses the gap, but that live frog has to be wired correctly through the turnout's points or it will short the moment a wheel bridges the wrong two rails. Insulfrog turnouts sidestep the wiring complexity entirely by making the frog electrically dead, at the cost of a genuine stall risk for short-wheelbase equipment crossing it.
On this page
What does a turnout number actually mean?
The number is exact geometry, not a style choice. It sets the frog angle and the length the turnout takes up.
A number 4 turnout has a sharper frog angle and takes less space than a number 8, which is gentler and suits longer equipment better.
| Number | Relative frog angle | Length vs a number 4 | Best suited to |
|---|---|---|---|
| 4 | Sharpest of the common numbers | Shortest, uses the least space | Tight yards and industrial spurs with short equipment |
| 6 | Moderate | Noticeably longer than a number 4 | The common all-purpose choice on a home layout |
| 8 | Gentle | Longer again | Main line running and longer passenger equipment |
| 10 | Gentlest of the common numbers | Longest, uses the most space | High speed main line divergence, large layouts with room to spare |
See number 4 vs number 6 turnout and number 6 vs number 8 turnout for the exact geometry difference between adjacent numbers.
How do you install a turnout and switch machine step by step?
- Choose the turnout number for the location. A sharp manual turnout such as Atlas Code 83 Nickel Silver Manual Snap Switch Left HO Scale fits a tight yard or industrial spur where space is at a premium. A number 6 such as Atlas HO Code 83 Number 6 Left-Hand Super Switch or Peco HO Scale Code 83 Electrofrog Number 6 Right-Hand Turnout suits most main line and yard ladder locations on a home layout. Longer equipment and higher speed running want a number 8 like Atlas Code 100 Nickel Silver Mark 4 Number 8 Turnout Left Hand HO Scale where the space allows it.
- Decide between electrofrog and insulfrog. Choose an electrofrog, live frog turnout such as Peco HO Scale Code 83 Electrofrog Number 6 Right-Hand Turnout or Peco HO Scale Code 100 Electrofrog Number 6 Right-Hand Turnout if short-wheelbase locomotives with few pickup wheels will cross it regularly. Choose a simpler insulfrog, dead frog turnout if wiring simplicity matters more and stalling is not a concern for the equipment involved.
- Test fit before fastening anything permanently. Lay the turnout in place with adjoining track and run the locomotives that will actually use it, checking for binding through the points and a smooth ride across the frog, before spiking, gluing or ballasting anything.
- Wire the frog correctly on an electrofrog turnout. An electrofrog frog is powered by the position of the points and needs its polarity switched with them, either through the turnout's own internal contacts or an auxiliary switch on the machine. Skipping this step, or wiring the frog to a fixed polarity, is the single most common cause of a dead short at a turnout.
- Mount the switch machine and connect the throwbar. A manual machine such as Atlas Code 83 Nickel Silver Manual Snap Switch Left HO Scale needs only a mechanical link to the throwbar. A remote or DCC-controlled machine like Atlas HO Code 83 Remote Right-Hand Turnout with Switch Machine needs its own wiring run back to a control panel or accessory decoder, kept separate from the track power bus.
- Test under power before ballasting. Run every locomotive that will use the turnout, in both directions and through both routes, checking for stalls at the frog and for any short as the points throw. Fix electrical problems now, since they are far harder to diagnose once ballast is glued around the mechanism.
Why would a short locomotive stall specifically on an insulfrog turnout?
An insulfrog frog is a small gap of electrically dead plastic, and a locomotive with only two or three powered axles, all clustered close together, can have every one of its pickup wheels sitting on that dead section at the same moment while crossing it. A longer locomotive, or one with pickups spread further along its wheelbase, always has at least one wheel on live rail during the same crossing and never notices the gap. This is a purely mechanical fact about wheelbase and pickup spacing, not a quality difference between the two frog types, and it is exactly what an electrofrog turnout's live frog avoids.
Adding a keep-alive capacitor to a short locomotive's decoder is a common workaround that solves the problem without changing the turnout at all, useful when a layout already has insulfrog turnouts installed and rewiring them is not practical.
What is a wye turnout used for?
A wye turnout diverges in both directions from a straight line rather than keeping one route straight and one curved, splitting roughly evenly to the left and right. A product like Atlas Code 83 Nickel Silver Wye Turnout HO Scale in HO or Kato N Scale Number 2 Electric Wye Turnout in N is used where a track plan genuinely needs two equally diverging routes, such as a balloon track or a triangular turning arrangement, rather than the more common situation of a straight main line with a single diverging spur.
Most home layouts use far more standard left and right hand turnouts than wyes, since the typical need is a spur or siding branching off an otherwise straight route. A wye is worth reaching for specifically when the track plan calls for symmetry, not as a general purpose substitute for a standard turnout, and its two diverging legs are usually built to the same number so equipment handles either route identically.
Atlas or Peco, and does the brand matter for this decision?
Both brands make both frog types, so the electrofrog versus insulfrog decision is separate from the brand decision. What differs between Atlas HO Code 83 Remote Right-Hand Turnout with Switch Machine and Peco HO Scale Code 83 Electrofrog Number 6 Right-Hand Turnout is more about tie spacing, rail profile match to your existing track, and switch machine compatibility than about frog type. See Atlas vs Peco turnouts and electrofrog vs insulfrog turnouts for the two decisions kept separate.
Sources
- Manufacturer published turnout geometry and wiring instructions
- NMRA published turnout and frog terminology
Frequently asked questions
What does turnout number mean?
It is the rate the diverging route pulls away from the straight one, measured at the frog: a number 6 moves one unit sideways for every six units of forward travel. Higher numbers are gentler and longer, suiting longer equipment and higher speed running, while lower numbers are sharper and fit tighter spaces such as an industrial spur or a compact yard ladder.
Should I use electrofrog or insulfrog turnouts?
Electrofrog if short-wheelbase locomotives with few pickup wheels will cross the frog regularly and stalling is a real concern, provided you wire the frog polarity correctly. Insulfrog if simpler wiring matters more than stall prevention, which is the safer default for a first layout or for equipment with plenty of pickup wheels.
Why does my turnout short when a train crosses it?
Almost always an electrofrog turnout with its live frog wired to a fixed polarity instead of one that switches with the points. Check that the frog polarity actually changes as you throw the points, either automatically through the turnout's own contacts or through an auxiliary switch on the machine.
Why does a short locomotive stall crossing certain turnouts?
This usually happens on an insulfrog turnout, where the frog is a small electrically dead gap. A locomotive with few powered pickup wheels clustered close together can have all of them briefly sitting on that dead section at once. An electrofrog turnout, wired correctly, avoids this because its frog stays live.
What turnout number should a home layout use for most locations?
A number 6 is the common all-purpose choice, gentle enough for most equipment while staying a manageable length for a home layout. Use a number 4 only where space is genuinely tight, such as an industrial spur, and reserve a number 8 or higher for main line divergences where longer equipment and higher speeds matter.
Do I need a switch machine, or can I throw turnouts by hand?
A manual throw with a ground throw or a simple mechanical linkage works fine for any turnout you can physically reach. A switch machine becomes worth the wiring for turnouts hidden in staging, out of reach behind scenery, or wherever remote or DCC control from a panel or throttle is genuinely useful.
Researched, not professional advice. This page is compiled from published manufacturer specifications, instruction manuals, published NMRA standards and recommended practices, and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are hobby convention rather than a standard, and they are labelled that way wherever they appear. Always check a radius, a clearance or a grade against your own equipment before you cut wood or lay rail, because manufacturers vary and so does what your specific models will tolerate. Any permanent mains wiring in a layout room is work for a licensed electrician to your local code.