DIN Rail Guide: 35 mm Standard, Rail Types and Mounting Rules

A DIN rail is a standardised metal profile — almost always 35 mm wide — that lets circuit breakers, energy meters, terminal blocks, relays and surge protective devices clip into a panel without a single screw through the device. The rail is fixed to the backplate, the spring clip on the back of each device grips the rail's flanges, and the panel becomes a modular assembly you can build, wire, test and service in place.

Three numbers decide whether a project fits together: the profile family (TS35 is the default), the rail height (7.5 mm or 15 mm), and the module width of the devices being mounted (normally a multiple of 17.5 mm). Plating, steel thickness, slot pattern and end stops do not change what fits — they decide how long the assembly survives.

Why the 35 mm profile became the default

The rail is specified in EN 60715, which grew out of the older German DIN 46277-3 standard — that is where the everyday name comes from. The important consequence is interchangeability: a compliant TS35 device from one manufacturer clips onto a compliant TS35 rail from another, which is why panel builders can mix meters, breakers and terminals from several suppliers on one run.

The top-hat shape does the work. The flat top face gives the device a stable seating plane, and the two flanges give the spring clip something to pull against, so the device is held by friction and spring force rather than by a fastener. That is also the weakness: friction holds vertically but not laterally, which is why end stops exist.

The four profiles you will actually meet

If you are quoting a replacement panel or adding devices to an existing one, photograph the rail and measure across the top face before ordering. A 32 mm rail looks close enough to 35 mm in a photo and nothing will clip onto it.

The dimensions that decide fit

• Width across the top face — 35 mm for TS35. This is the only dimension that decides whether a device clips on.
• Height — 7.5 mm standard, 15 mm deep. Height changes clearance and stiffness, not compatibility.
• Material thickness — thin rail (around 1 mm) is normal for panel runs; longer unsupported runs and heavy devices need thicker section.
• Length — 1 m and 2 m are the usual stock lengths; cut to the panel width and keep the offcut.
• Slots versus plain — slotted rail allows position adjustment and fits varying backplate layouts; plain rail is stronger and needs drilled fixing points.
• Material — zinc-plated steel is the default; aluminium is lighter and more corrosion-resistant but has weaker threads.

How many devices fit on one rail

Device widths are expressed in modules, and one module is 17.5 mm under DIN 43880 (some product families use 18 mm, so check). That makes the arithmetic simple: a 1 m rail carries about 57 modules, a 2 m rail about 114.

Plan for roughly 20 % spare capacity on a new panel. Filling a rail to its last module leaves no room for a future circuit, and later additions mean re-terminating a whole run instead of clipping in one device.

Mounting rules that prevent callbacks

• Support the rail properly. Fix it at both ends and at intervals across the span. An unsupported middle flexes when a device is pushed on, and a flexed rail releases clips.
• Fit end stops at both ends of every run. They are the only thing preventing lateral creep when neighbouring devices are inserted or wired.
• Tighten the rail before loading it. Loading devices onto a loose rail distorts the profile and makes the clip grip unevenly.
• Cut square and deburr. A burr stops the clip seating fully and, on devices that use the rail for protective earthing, produces an intermittent earth.
• Earth the rail where devices rely on it. Many surge protective devices and filters take their earth reference from the rail, so a painted or insulated mounting surface is not acceptable.
• Never mix 7.5 mm and 15 mm rail mid-run. Devices sit at different depths and the wiring plane breaks.
• Respect grouping heat. Devices mounted side by side derate; leave the spacing the datasheet asks for rather than packing a rail solid.

Material, plating and corrosion

Zinc-plated steel covers indoor panels and is what most projects should specify. Aluminium rail suits damp or coastal sites where weight and corrosion matter more than thread strength. Stainless rail belongs in washdown or food environments. In humid locations, check the fastener material against the rail: steel screws in an aluminium rail corrode at the joint, and the corrosion products raise resistance exactly where the earth path runs.

What to send with an RFQ

• Rail profile and height (TS35 × 7.5 mm, for example) and total length per panel.
• Device list with module widths, so the rail length and spare capacity can be checked.
• Enclosure depth, if any device is taller than a standard module.
• Environment: indoor, coastal, washdown, or high ambient temperature.
• Whether the rail is part of the protective earthing path.

YOMIN devices that mount on 35 mm rail

The rail is only half the assembly, so it is worth buying the devices and the rail against the same drawing. YOMIN builds DIN-rail hardware across four product families:

• DIN-rail terminal blocks — brass current bar in a PA housing with copper inlet and outlet, and the FJ6D-200 guide-rail connection terminal for panel feed-through.
• DIN-rail energy meters — including a seven-module three-phase four-wire Wi-Fi meter rated 3×5(80) A without relay, for sub-metering inside a distribution board.
• DIN-rail voltage protection — self-resetting over and under voltage protectors with adjustable overcurrent and leakage settings.
• DIN-rail surge protection — Type 2 devices for AC and PV circuits.

Browse the terminal and connector range, the DIN-rail energy meters or the fuse and protection range for the device side of the assembly. For wiring detail on the same profile, read our DIN rail terminal block guide and the step-by-step wiring walkthrough; if you are choosing between mounting styles, DIN rail versus panel meters compares the two. Meter accuracy classes are covered in the accuracy class guide.

Frequently asked questions

Is a DIN rail always 35 mm wide?

No. The 35 mm top-hat profile (TS35) is the default for industrial and commercial panels, but 15 mm and 32 mm profiles also exist. Always read the device datasheet before ordering rail, because a 35 mm device will not clip onto a 15 mm rail.

What is the difference between 7.5 mm and 15 mm DIN rail?

Both are 35 mm wide. The 15 mm version is deeper and stiffer, which gives more clearance behind the devices and better support for tall or heavy components, but it also consumes depth inside a shallow enclosure.

Do I need end stops on a DIN rail?

Yes for any run of spring-clip devices. The clip grips vertically but does not stop lateral movement, so end stops at both ends of the run keep devices from sliding when a neighbour is inserted, removed or wired.

Can DIN rail be cut on site?

Yes, with a rail cutter or a fine-tooth hacksaw. Cut square and deburr both edges, because a burr stops the clip seating fully and produces an intermittent earth connection on devices that rely on the rail for protective earthing.

Will YOMIN DIN-rail meters fit an existing 35 mm rail?

YOMIN DIN-rail meters, terminal blocks, voltage protectors and surge protective devices are built for 35 mm top-hat rail. For deep or tall devices, confirm whether the enclosure gives enough clearance for a 15 mm rail.