DIN Rail Types and Control Panel Layout
Short answer
- A control panel layout starts by matching the DIN-rail profile to the equipment, then arranging wiring and components so noise, temperature rise, and maintenance access stay within acceptable limits.
- The 35 mm top-hat rail (TS35) is the industrial standard, available in 7.5 mm and 15 mm depths, while power, control, and signal wiring are kept in separate zones and heat-generating devices sit near the top.
- Grounding runs to a dedicated earth bar, with a mechanical bond through painted panels, and ducts keep fill limits and 75 mm of front clearance for access.
When a control panel is built, the first question is which DIN‑rail profile will carry the devices and how the internal layout will keep power, signal, and heat from interfering with each other. The answer lies in matching the rail geometry to the equipment, then arranging the wiring and components so that noise, temperature rise, and maintenance access are all within acceptable limits.
What DIN rail profiles are available and when are they used?
The 35 mm top‑hat rail – often called the TS35 – is the de‑facto industrial standard. Its 35 mm width fits the mounting slots of virtually every modern terminal block, relay, and power module. The rail is offered in two common depth options:
- 7.5 mm depth: used when space is at a premium and the mounted devices are low‑profile (e.g., solid‑state relays, small signal modules).
- 15 mm depth: provides a larger mounting surface for heavier devices such as motor starters, contactors, or fused disconnects. The extra depth also improves rigidity, reducing rail deflection under load.
For very compact applications, the miniature 15 mm top‑hat rail exists. Its reduced width (15 mm) allows dense packing of low‑profile devices, but it cannot accept the standard 35 mm modules; you must use miniature‑compatible components.
The G‑profile rail (sometimes called the G‑rail) has a 32 mm width and a “G” shaped cross‑section. It is popular in European‑type panels where the rail is mounted on the back side of a panel and devices are inserted from the front. The G‑rail offers a larger mounting surface than the 35 mm top‑hat, which can be advantageous for heavy‑duty devices that need more screw engagement.
All of these rails are supported by a range of brackets, end‑caps, and mounting hardware. For a full list of compatible accessories, see our DIN rail and mounting hardware catalogue.
How do you choose the right DIN rail for a panel?
Selection is driven by three practical factors:
- Mechanical load: A contactor with a 30 A rating can weigh several kilograms. Use a 15 mm depth TS35 or a G‑profile with adequate screw spacing to prevent rail sag.
- Device density: If you need to fit many signal modules in a limited space, the 7.5 mm depth TS35 or the miniature 15 mm rail will keep the panel depth down.
- Future expansion: Leave at least one spare slot of each rail type you plan to use. Adding a new module later is far easier when the rail length is not fully populated.
When mounting the rail, ensure the mounting holes align with the panel’s pre‑drilled holes or use a suitable back‑plate. A misaligned rail can cause uneven screw torque, leading to premature fatigue.
How should power, control, and signal wiring be separated?
Noise coupling is the most common cause of intermittent faults in mixed‑signal panels. The basic rule is to keep high‑current, high‑frequency conductors physically separate from low‑level signal loops.
- Power zone: Place mains and DC bus bars, fuse blocks, and contactor terminals on one side of the rail. Keep these conductors in a dedicated conduit or wire duct.
- Control zone: Locate PLC I/O, relay coils, and low‑voltage control wiring on the opposite side of the rail. Use separate wireways to maintain a minimum 50 mm clearance where possible.
- Signal zone: Sensor and communication cables (e.g., 4‑20 mA loops, fieldbus, Ethernet) should run in their own ducts, preferably with metal‑shielded cable if the environment is electrically noisy.
Variable‑frequency drive (VFD) output cables are a special case. The high‑frequency switching edges generate common‑mode voltage that can easily couple into nearby signal wiring. The recommended practice is:
- Run the VFD output cable in a separate conduit that is routed away from the control zone for as long as practical.
- If the VFD cable must cross a signal duct, do so at a right angle and maintain at least a 25 mm clearance between the conductors.
- Terminate VFD output cables in a shielded terminal block and connect the shield to the earth bar at a single point to avoid ground loops.
For detailed guidance on routing ducts and fittings, refer to our wireways and fittings section.
Where should heat-generating devices go in a panel?
Heat rises, so placing the hottest components near the top of the panel helps natural convection. A typical thermal hierarchy looks like this:
- Top row: VFDs, motor‑starter contactors, and large power supplies. These devices often have built‑in fans or heat sinks that benefit from unobstructed airflow.
- Middle row: Medium‑power devices such as PLC power modules and medium‑size breakers.
- Bottom row: Low‑power signal modules, terminal blocks, and communication cards.
Leave at least 15 mm of vertical clearance above any heat‑generating device to allow air to circulate. If the panel is enclosed in a wall‑mount enclosure, ensure the enclosure’s ventilation slots are aligned with the hot zones.
Thermal calculations are straightforward: a device’s power loss (W) divided by the ambient air flow (m³/s) gives an approximate temperature rise. When the rise exceeds the device’s rated temperature, add a fan or relocate the device lower in the stack.
How full can a wire duct be, and how much access is needed?
Proper duct fill prevents overheating of cables and makes future modifications easier. The NEC and IEC standards both limit the fill to 40 % of the duct’s cross‑section for single‑conductor cables, and 30 % when multiple conductors share the same duct.
Practical steps:
- Calculate the total cross‑sectional area of all conductors that will occupy a duct.
- Select a conduit size that leaves at least 40 % free space.
- Use pull‑string or cable‑drag devices when installing long runs to avoid damaging insulation.
- Label each duct at both ends; a simple alphanumeric code (e.g., "PWR‑01", "SIG‑A") saves time during troubleshooting.
Maintain a clear front clearance of at least 75 mm in front of any terminal block or switch. This space is required for safe hand access, tool clearance, and to meet lockout‑tagout (LOTO) procedures.
How do you ground and bond a painted control panel?
A reliable grounding scheme starts with a dedicated earth bar mounted to the panel chassis. All power‑ground conductors, chassis grounds, and protective earth (PE) connections terminate on this bar.
When using painted or powder‑coated panels, the paint can act as an insulating layer, breaking the low‑impedance path required for fault currents. The remedy is to provide a mechanical bond:
- Drill a small (≈3 mm) hole through the paint at the location of the earth bar.
- Insert a copper bonding screw or a stainless‑steel grounding lug that penetrates the panel’s metal substrate.
- Secure the earth bar to this lug with a torque that meets the manufacturer’s specification (typically 5–7 Nm for M4 screws).
For the actual termination of ground and protective‑earth conductors, use dedicated ground and PE terminal blocks. These blocks feature a low‑resistance path and often include a screw‑type clamp that guarantees a solid mechanical and electrical connection.
Remember that all grounding work must be performed by qualified personnel. Improper bonding can increase the risk of arc‑flash incidents and violate safety regulations.
What does a sample control panel layout look like?
Consider a 600 mm × 400 mm wall‑mount panel that houses a 5 kW VFD, a PLC, three contactors, and a suite of analog and digital I/O modules. A practical layout would be:
- Mount a 15 mm depth TS35 rail along the top edge. This rail carries the VFD, contactors, and the PLC power supply.
- Install a second 7.5 mm depth TS35 rail below the first. Use it for low‑profile I/O modules and signal terminal blocks.
- Run a dedicated conduit for the VFD output cable. Route it along the right side of the panel, keeping at least 50 mm from the signal rail.
- Place a wireway on the left side for all control and signal wiring. Use the wireways and fittings to keep bundles organized and to provide a clear path for future additions.
- Mount the earth bar on the rear of the panel. Drill through the paint, install a copper bonding screw, and terminate all PE conductors to the bar using the ground and PE terminal blocks.
- Leave a 75 mm front clearance in front of the I/O rail. This satisfies maintenance access and LOTO requirements.
With this arrangement, power conductors are isolated from low‑level signals, the VFD’s high‑frequency output is kept away from sensitive loops, heat‑generating devices are positioned for natural convection, and the grounding path is mechanically sound despite the painted enclosure.
If you need help selecting the appropriate DIN‑rail accessories, wireway components, or grounding blocks for a specific panel design, feel free to contact us for sourcing assistance.
Related reading: what a subpanel is and how to lay one out; what a power distribution block is; cable routing and wire management basics.
Related: Wiring Duct: Selection, Fill and Routing in Panels.
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Request a QuoteFrequently asked questions
What is the difference between 7.5 mm and 15 mm TS35 DIN rail?
The 7.5 mm depth suits tight spaces and low-profile devices such as solid-state relays and small signal modules, while the 15 mm depth suits heavier devices such as motor starters, contactors, or fused disconnects. The 15 mm depth also adds rigidity, reducing rail deflection under load. Both are 35 mm top-hat rail.
How should power and signal wiring be separated in a control panel?
Power, control, and signal wiring should be kept physically separate, with high-current conductors apart from low-level signal loops. Control wiring uses separate wireways with a minimum 50 mm clearance where possible. Sensor and communication cables run in their own ducts, preferably with metal-shielded cable in an electrically noisy environment. Noise coupling is the most common cause of intermittent faults in mixed-signal panels.
How should VFD output cables be routed in a control panel?
VFD output cables should run in a separate conduit routed away from the control zone for as long as practical. If the cable must cross a signal duct, it crosses at a right angle with at least 25 mm clearance between conductors. The cable terminates in a shielded terminal block, with the shield connected to the earth bar at a single point to avoid ground loops.
How do you ground a painted control panel?
Paint can act as an insulating layer that breaks the low-impedance fault path, so a mechanical bond is needed. Drill a small hole of about 3 mm through the paint at the earth bar location, then insert a copper bonding screw or stainless-steel grounding lug that penetrates the metal substrate. Secure the earth bar with torque meeting the manufacturer's specification, typically 5–7 Nm for M4 screws.