DIN rail sizes explained: TS35 and beyond

What DIN rail is, and why size matters

DIN rail is the metal strip that components clip onto inside a control panel. Terminal blocks, circuit breakers, relays, power supplies, PLC I/O and small drives all mount on it, so you can lay out, wire and later swap parts without drilling the back panel for each one.

The name comes from the German standards body Deutsches Institut für Normung, which published the original specs. Today the common profiles sit under international standards, chiefly IEC/EN 60715. Because the dimensions are standardized, a TS35 terminal block from one maker clips onto TS35 rail from another.

Size matters for three reasons: the component’s mounting foot has to match the rail profile, the rail has to carry the weight without flexing, and the rail’s depth sets how far devices stand off the back panel, which affects wiring room and enclosure depth.

TS35: the standard top-hat rail

TS35 is called “top hat” rail because its cross-section looks like a hat with a brim. The flat center fastens to the back panel, and devices clip over the two outer edges. The overall width is 35 mm. What changes between the two versions is depth.

TS35 × 7.5 mm

This is the default for terminal blocks, miniature circuit breakers, interface relays, DIN-mount power supplies and most PLC modules. It’s light, inexpensive and fits shallow enclosures. If a drawing just says “35 mm DIN rail,” this is usually what it means.

TS35 × 15 mm

The deeper profile is much stiffer. Choose it when you mount heavy devices such as larger contactors, transformers or motor starters, when the rail spans a long distance between fasteners, or when you want extra room behind devices to route wire. Because the top edges match the shallow version, anything rated for TS35 clips on.

DIN rail sizes compared

TS35 covers most new work. The other profiles show up in compact enclosures, older machines and some specialty equipment.

Beyond TS35: the profiles you’ll meet on retrofits

TS15 miniature rail

At 15 mm wide, TS15 suits small terminal blocks and miniature relays inside junction boxes and instrument housings where a 35 mm rail won’t fit. Components are not interchangeable with TS35, so check the mounting foot before ordering.

G32 rail

G rail has an asymmetric profile, with one lipped edge that hooks the device and a lower edge it snaps against. It was common on panels built before top hat took over and you’ll still find it on older machines. Some terminal blocks have feet that fit both G32 and TS35, which helps during a rebuild.

C-rail

C-section rail is open on one side and comes in several widths. You’re most likely to see it on legacy equipment. On new builds, standardize on TS35 unless a specific component requires something else.

Materials and slotted vs. solid rail

Once you’ve picked a profile, two choices remain.

• Material. Zinc-plated steel is the standard for general panels. Aluminum saves weight and doesn’t rust, but it’s softer and can deform under heavy components. Stainless steel is for washdown, food and outdoor enclosures. Copper rail is used where the rail itself carries a ground connection.
• Slotted or solid. Slotted rail has a row of elongated holes, so you can fasten it anywhere along its length and it weighs less. Solid (unslotted) rail is stiffer and is the better choice when you need to drill at exact positions.

Steel and copper rail can also serve as a grounding path when you use ground terminal blocks that clamp directly to the rail. The rail still needs to be bonded to the panel’s ground point, so treat it as part of the grounding design rather than a substitute for it.

How to choose the right DIN rail

1. Match the components. Check the mounting spec on every device going on the rail. If it says TS35 or 35 mm, you have both depths to choose from.
2. Check weight and span. Light terminals and relays are fine on 7.5 mm rail. Heavier devices or long runs between fasteners point to 15 mm.
3. Check enclosure depth. Add rail depth, device depth and door clearance. Deep rail adds 7.5 mm, which matters in shallow boxes.
4. Pick the material for the environment. Steel for general use, stainless for washdown or outdoor, copper if the rail is part of your ground path.
5. Plan the length with spare space. Leave room for end stops, labels and future additions. A common rule of thumb is 20 to 25 percent spare.

Planning rail length: a quick example

Terminal block widths vary by wire size and type, so pull the actual widths from the datasheet. Here’s how the math works for one illustrative row.

DIN rail usually comes in 1 m or 2 m lengths and is cut on site with a rail cutter or hacksaw. Deburr the cut ends so devices slide on cleanly, and fasten the rail at regular intervals per the manufacturer’s guidance.

DIN rail FAQ