How to Choose the Right DIN Rail: A Selection Guide for Electrical Cabinet Assembly (2026)

To choose a DIN rail, first decide what the rail must do — mechanical mounting only, or mounting plus protective earthing. Then select the profile and size from IEC 60715 (35 × 7.5 mm top-hat for most components, 35 × 15 mm where load or span is higher), then the material and surface finish, and finally whether cut-to-length, pre-punched or pre-assembled rails save more assembly time than they cost. If the rail is part of an earthing path, check its equivalent copper cross-section and short-time withstand current under IEC 60947-7-2 rather than assuming any metal rail is adequate.

A DIN rail is a standardized metal mounting rail that holds circuit breakers, relays, PLCs, power supplies and terminal blocks inside a cabinet or distribution box. "DIN" refers to the Deutsches Institut für Normung. The rail dimensions were later carried into European (EN 60715) and international (IEC 60715) standards, which is why a 35 mm rail from one supplier accepts components from another.

The rail's primary job is mechanical support. It is not a busbar and should not be planned as a current-carrying conductor. Because it is metal, however, it is usually bonded to the enclosure and used to earth the components that clip onto it — for example, PE terminal blocks that contact the rail foot directly. That second role changes the material decision, so record it at the start of the design: "mounting only" or "mounting + earthing".

Three cross-sections are still in use:

For top-hat rails, IEC 60715 defines the 35 mm width with two heights:

A narrower 15 mm rail (TS 15) suits very small components but is far less interchangeable than TS 35. Before ordering, check three points against each component datasheet: rail width, rail height (some components need the 15 mm depth for clearance or stability) and whether a slotted rail is acceptable for the fixing method.

Material follows the function defined in the first step.

Steel (zinc-plated, usually passivated) is the default. It is strong, low-cost and widely stocked, and it covers almost all mounting-only applications. Its conductivity and short-time withstand are the lowest of the three.

Aluminum conducts better than steel and is lighter, but its oxide layer raises contact resistance, so contact surfaces need attention when the rail is in an earthing path.

Copper has the highest conductivity and short-time withstand current. It is used where the rail itself must carry earth-fault current, at a much higher material cost.

When a rail serves as the conductor for PE terminal blocks, manufacturers rate it by an equivalent copper cross-section and a 1 s short-time withstand current per IEC 60947-7-2 (120 A/mm² × cross-section). Published values:

Two rules follow. First, a steel rail can earth PE terminal blocks up to its rated equivalent cross-section, but steel may not be used as a PEN conductor under IEC 60947-7-2. Second, automation vendors' installation guides commonly specify zinc-plated, chromate-passivated steel rail for equipment earthing, because untreated aluminum can oxidize and give unstable earth resistance (see the IEEE PES white paper on DIN rail). Higher conductivity on paper does not guarantee a stable earth contact over years of service.

In procurement, request the electrical data sheet for the exact profile, thickness and material rather than reusing a value from a different rail.

Standard 1 m or 2 m lengths suit most projects. Customization becomes worthwhile when cabinets are non-standard, layouts are tight or holes must match a fixed pattern. A complete inquiry should define:

A supplier that offers controlled drawings, sample approval and repeat-order consistency makes a custom rail easier to manage as a stable part number.

DEGSON lists its NS35 top-hat rails, including the NS35/7.5-1000-00A(H), among the accessories for its DIN rail terminal blocks (product search); DEGSON terminal block datasheets such as DS10 name this rail as the mounting accessory. For the rail's material, thickness, finish and earthing data, or for a custom length or slot pattern, contact DEGSON technical support with your drawing.

In the conventional workflow, the panel builder buys bare rails, terminal blocks, end plates, partitions, jumpers and markers separately and assembles them in the shop. The hidden costs are incoming inspection of many loose parts, storage, assembly labor, line stops for missing parts and positioning errors.

A pre-assembled rail is delivered with terminals and accessories mounted to the drawing, marked and continuity-checked. Its effects:

Pre-assembly is not always the better choice. For highly standardized cabinets with strong in-house capacity and favorable loose-part pricing, in-house assembly can remain cheaper. It pays off most for builders trying to shorten lead time, reduce work-in-progress and keep quality stable across many low-volume variants.

DEGSON supplies the terminal blocks that populate these rails — for example the push-in DS2.5 (IEC 800V/24A, UL 600V/20A, 0.14–4 mm²) and the screw-type DC2.5 (IEC 800V/24A, UL 600V/25A), both to IEC 60947-7-1 — and offers pre-assembled rails as a value-added service, quoted against the customer's rail drawing and terminal list.

Can a steel DIN rail be used for protective earthing?

Yes, for PE terminal blocks within its rated equivalent cross-section — 16 mm² and 1.92 kA for 1 s for a typical zinc-plated 35 × 7.5 mm steel rail. It may not be used as a PEN conductor.

Should I choose 35 × 7.5 mm or 35 × 15 mm?

Start with 35 × 7.5 mm, which most components are designed for. Move to 35 × 15 mm when components are heavy, spans between fixing points are long, or a component datasheet requires the extra depth.

Next step: search DEGSON NS35 rails and DIN rail terminal blocks at degson.com.cn, 内部工具 datasheets and CAD, or contact DEGSON technical support with your rail drawing and terminal list for rail data, custom rails or pre-assembled rail support.