Comb Rail or Busbar System - Which to Use for Feeding?
Comb rails and busbar systems distribute the incoming supply to modular DIN-rail devices in the enclosure. This guide explains when a compact comb rail is enough and when a high-capacity busbar system makes sense - including current rating, pole count and finger safety per IEC 61439.
View distribution productsWhat separates a comb rail from a busbar?
A comb rail (also insulated busbar or pin busbar) is a prefabricated connecting bar that feeds several adjacent DIN-rail devices in parallel. It looks like a comb: one continuous copper conductor with tap-offs at the standard 18 mm pitch. A busbar system, by contrast, is a horizontal bar assembly mounted in the enclosure from which individual outgoing circuits branch off via adapters.
The comb rail replaces loose single-wire jumpers between miniature circuit breakers or residual current devices. That saves wiring time, cuts error sources and produces a clean, repeatable board layout. The busbar system is the higher-level distribution stage for larger currents and many outgoing circuits.
- 18 mm pitch: matches standard modular devices (1 module = 17.5 mm).
- Versions in 1, 2, 3 and 4 pole for single, split and three-phase distribution.
- Three-phase combs use staggered pins (L1-L2-L3 alternating).
- Busbars are usually electrolytic copper, 5, 10 or 12 mm bar thickness.
When to pick a comb rail, when a busbar system?
The choice comes down mainly to rated current and the number of outgoing circuits. Comb rails cover classic residential and commercial distribution, while busbar systems start where currents and selectivity demands rise.
As a working rule: up to around 125 A and a manageable number of identical outgoing circuits, the comb rail is the fastest and most economical solution. As soon as multiple distribution panels, high short-circuit withstand or flexible circuits that change during operation are required, the busbar system plays to its strengths.
- Choose a comb rail: many identical breakers in one row, current up to about 125 A, fixed layout.
- Choose a busbar: high total currents, many panels, required short-circuit withstand Icw.
- Always rate the rail above the total load or the upstream protective device.
- Watch the permitted number of protected outgoing circuits and derating when devices are grouped.
What matters for safety and assembly?
Touch protection is mandatory. Comb rails ship with an insulating cover and must be closed off with an end cap at the cut interface to stay finger-safe. Compliance with IP2X touch protection and the stated short-circuit withstand is essential.
- Match the comb rail to the terminal width and connection type of the devices (pin or fork tap-off).
- After cutting, insulate open ends with an end cap and cover unused pins.
- Coordinate the rail short-circuit withstand with the upstream protective device.
- Follow the manufacturer approval for the rail / device combination (built assembly per IEC 61439).
Frequently asked questions
What does the 18 mm pitch mean on comb rails?
Modular DIN-rail devices have a module width of 17.5 mm. Comb rails are built to this roughly 18 mm pitch so the tap-offs land exactly on the terminals of adjacent devices.
How much current can a comb rail carry?
Common comb rails are rated for 63 to 125 A. The decisive value is the rated current at the feed point, because with single-end feeding the rail carries the sum of all outgoing circuit currents.
When is a busbar system worth it?
As soon as high total currents above 125 A, several distribution panels or a required short-circuit withstand come into play. The system also allows flexible outgoing circuits that can be changed during operation via adapters.
Must a comb rail be insulated after cutting?
Yes. After cutting to length, close the interface with an end cap so it stays finger-safe (IP2X) and cover any unused pins.
Looking for the right distribution gear?
We supply comb rails at 18 mm pitch, busbar systems and matching accessories including end caps and touch protection - coordinated to IEC 61439.
Standard tested
Components per IEC 61439 for built assemblies.
Finger-safe
End caps and covers for IP2X included.
Right pitch
Comb rails at 18 mm pitch from stock.
Expert advice
Our specialists help you size the system.