Switchgear
Planning a low-voltage main distribution board (NSHV): a guide for commerce and industry
The main distribution board determines how safe, available and expandable a building's power supply is. This guide shows the most important planning steps – from the load calculation to routine verification.
TOKSEL Elektrotechnik editorial teamPublished on 5 min read
The low-voltage main distribution board (NSHV) is the heart of the power supply in commercial and industrial buildings. This is where energy arrives from the transformer or service connection (Hausanschluss) and is distributed to parts of the building, production areas and large loads. Planning errors often only become apparent years later – in the form of missing reserves, unnecessary shutdowns or expensive conversions. That is why it pays to clarify the most important points systematically from the outset.
1. Draw up a load calculation
It all starts with the question: how much power is really needed? To answer it, all loads are recorded and assessed using realistic simultaneity factors (Gleichzeitigkeitsfaktoren) – because not every machine runs at full load at the same time. A careful load calculation (Leistungsbilanz) prevents both expensive oversizing and later bottlenecks.
Factor in the future as well: charging infrastructure under the GEIG, heat pumps, photovoltaics, battery storage and new production equipment all increase power demand. A reserve of 20 to 30% in capacity and space has proven itself in practice.
2. Define the network type and earthing concept
In modern commercial and industrial installations, a TN-S system with separate neutral and protective conductors from the main distribution board onwards is standard. Combined with a central earthing point (ZEP), it reduces stray currents on cable screens and pipework – important for the electromagnetic compatibility of IT and control systems.
3. Calculate short-circuit current and selectivity
The switchgear must be able to safely withstand the short-circuit current that can occur at its installation location. Decisive factors include the rated short-time withstand current (Icw) and the rated peak withstand current (Ipk) of the busbars as well as the breaking capacity of the protective devices.
Selectivity (discrimination) is just as important: in the event of a fault, only the protective device immediately upstream of the fault location should trip – not the main switch. Coordinated characteristics of circuit breakers and fuses ensure that the rest of the operation keeps running.
4. Choose the form of internal separation
DIN EN 61439-2 distinguishes between forms of internal separation from Form 1 to Form 4. They describe how busbars, functional units and terminals are segregated from one another.
| Form | Separation | Typical use |
|---|---|---|
| Form 1 | no internal separation | smaller distribution boards with low availability requirements |
| Form 2 | busbars separated from the functional units | commercial premises with moderate requirements |
| Form 3 | additionally, functional units separated from one another | where individual outgoing feeders are to be maintained during operation |
| Form 4 | additionally, the terminals of the functional units separated | high availability, e.g. production or data centres |
Higher forms improve protection when working on individual outgoing feeders and limit the effects of faults. However, they require more space and increase costs – so the choice should match the required availability.
5. Rated current, temperature rise and installation location
In addition to the rated current of the switchgear assembly (Schaltgerätekombination), temperature rise plays a major role: circuit breakers, fuses and busbars generate heat losses that must be dissipated. The switchroom therefore needs adequate ventilation and, if necessary, air conditioning.
The space available is also crucial: operating aisles must be sufficiently wide, doors must be able to open fully, and the room should remain accessible for maintenance, replacement and future extensions. The requirements for operating and maintenance gangways are set out in DIN VDE 0100-729.
6. Metering and energy management
Modern main distribution boards are more than just distributors. Multifunction meters and communication modules provide data on consumption, peak loads and power quality. This transparency is the basis for energy management – for example in accordance with ISO 50001 – and helps to avoid expensive peak loads.
7. Design verification and routine verification
Under DIN EN 61439, a design verification (Bauartnachweis) must be available for every switchgear assembly. It proves that the system used is suitable with regard to temperature rise, short-circuit withstand strength and insulation properties, among other things. As a rule, it is based on the verifications provided by the system manufacturer.
Before delivery, the switchgear manufacturer carries out the routine verification (Stückprüfung) on every single assembly: visual inspection, wiring, insulation properties, protective conductor connections and function. The results are documented and handed over together with the circuit diagrams and equipment labelling.
Experience from the region
We plan and build low-voltage main distribution boards and sub-distribution boards for commercial and industrial businesses in Cologne, Hürth and the Rhein-Erft district – from the incoming panel with circuit breaker to the NH fuse outgoing feeders for individual buildings. Find out more under Switchgear construction. If an existing system is to be modernised, also read our guide on switchgear retrofits.
Frequently asked questions
How long does it take to manufacture an NSHV?
That depends on the size, complexity and delivery times of the components. Allow sufficient lead time for coordination, manufacturing and testing – especially if large circuit breakers or special components are required.
Who is responsible for the design verification?
In principle, the manufacturer of the switchgear assembly. In practice, the manufacturer relies on the verifications provided by the system manufacturer and carries out the routine verification of each assembly itself.
Can an existing NSHV be extended?
Often yes – provided the short-circuit rating, temperature rise and space allow it and suitable system components are available. For older installations, a retrofit or an additional panel is often the more economical solution.
Related service
Switchgear construction
Low-voltage main distribution boards, sub-distribution boards and meter cabinets – engineered, built and tested to DIN EN 61439.
This article provides a general overview (as of October 2026) and does not replace an assessment or advice in the individual case. The applicable standards, laws and the requirements of your grid operator are decisive.
