The Role of Electrical Distribution Panels
The electrical distribution panel is the central point of any electrical installation. It receives power from the main source and distributes it in a controlled manner to individual circuits, providing protection for each circuit through dedicated devices (breakers, fuses, relays).
A well-designed and properly built panel guarantees three essential things: user safety, equipment protection, and continuity of supply. An undersized or non-compliant panel can lead to overheating, nuisance tripping, or — in extreme cases — fires.
Types of Electrical Panels
Main Distribution Board (MDB)
This is the first panel in the installation, fed directly from the electrical connection or transformer. Its role is to distribute power to sub-distribution boards and main circuits. The MDB typically contains:
- The main automatic circuit breaker
- Measuring devices (ammeters, voltmeters, or power analyzers)
- Main installation protection devices
- Changeover switches (for alternative sources, generators)
The MDB is sized based on the total installed power and the estimated maximum simultaneous demand.
Sub-Distribution Boards (SDB)
Fed from the MDB, sub-distribution boards serve specific zones or floors within a building. They enable logical segmentation of the installation, facilitating both operation and troubleshooting. The benefits of segmentation include:
- Fault isolation — a problem on one circuit does not affect the entire building
- Easy access to zone-level protection
- Reduced cable cross-sections on longer cable routes
Industrial Panels
Panels for industrial environments have additional requirements compared to residential or commercial ones:
- Mechanical robustness — metal construction resistant to vibrations and impacts
- Higher protection ratings — IP55 or IP65 for dusty or humid environments
- Ventilation — forced or natural, sized for heat dissipation
- Busbar systems — for high currents, replacing individual cables
- Separate compartments — per compartmentalization requirements (Forms 1-4b, EN 61439-2)
Proper Panel Sizing
Sizing an electrical panel involves several critical factors:
Installed Power and Diversity Factor
Not all circuits operate at maximum capacity simultaneously. The diversity factor (Ks) enables realistic sizing:
- Lighting: Ks = 0.8 - 1.0
- General socket outlets: Ks = 0.3 - 0.5
- Industrial equipment: Ks = 0.5 - 0.8 (depends on the technological process)
Short-Circuit Current
The panel must withstand the maximum possible short-circuit current at the point of installation. This is calculated based on the total upstream circuit impedance and determines:
- The breaking capacity of circuit breakers
- The mechanical and thermal resistance of busbars
- Protection coordination (selectivity)
Spare Capacity
Best practice requires maintaining at least 20-30% free space in the panel for future expansion. An installation that evolves with the company’s needs saves significant costs over time.
IP Protection Ratings
The IP (Ingress Protection) rating defines the panel’s resistance to solid objects and water penetration. The appropriate IP rating depends on the installation environment:
| IP Rating | Protection | Typical Use |
|---|---|---|
| IP20 | Protection against direct contact | Clean indoor spaces, offices |
| IP30 | Protection against objects > 2.5 mm | Standard indoor spaces |
| IP44 | Protection against splashing | Semi-outdoor spaces, garages |
| IP55 | Protection against water jets | Industrial environments, technical rooms |
| IP65 | Full dust and jet protection | Harsh industrial environments |
| IP66 | Protection against powerful jets | Outdoor, washdown areas |
Selecting an insufficient IP rating compromises safety and panel durability. Selecting an excessive rating increases costs without real benefits.
The EN 61439 Standard
The EN 61439 standard is the primary reference for low-voltage switchgear and controlgear assemblies in Europe. It replaced the older EN 60439 standard and introduced several important changes:
Key Requirements
- Design verification — the original manufacturer must demonstrate conformity through calculations, tests, or comparison with reference designs
- Routine verification — each manufactured panel must be individually verified (continuity, insulation, operation)
- Temperature limits — maximum permissible temperatures for components and connections, verified by measurement or calculation
- Short-circuit withstand — demonstrated through testing or calculation per standardized methods
Forms of Internal Separation
The standard defines four forms of internal separation, with increasing complexity and cost:
- Form 1 — no internal separation (simplest)
- Form 2 — separation between busbars and functional units
- Form 3 — separation between all functional units and from busbars
- Form 4 — complete separation, including connection terminals
The choice of form depends on operational requirements: the ability to work on one circuit without shutting down others, the required safety level, and the available budget.
Component Selection
The components of an electrical panel must be selected as an integrated system, not as individual parts:
- Circuit breakers — coordinated for selectivity (a fault trips only the nearest protection device)
- Residual current devices (RCDs) — type AC, A, or B, depending on the type of connected loads
- Contactors — sized for the appropriate utilization category (AC-1, AC-3, etc.)
- Busbars — cross-sectioned for both rated current and short-circuit current
- Terminal blocks — certified for the cable cross-sections used
- Surge protection devices (SPDs) — type 1, 2, or combined, depending on the installation point
Labeling and Documentation Requirements
A compliant electrical panel must be accompanied by:
- Updated single-line diagram reflecting the actual state of the installation
- Clear labeling of each circuit (identification, destination, rated current)
- Panel nameplate (manufacturer, reference standard, rated current, IP rating)
- Operating and maintenance instructions
- Verification certificate issued at commissioning
Documentation must be kept throughout the panel’s service life and updated with every modification.
Steiner Systems is ANRE certified and an official R&M Partner. Contact us for the design and construction of electrical distribution panels compliant with the latest standards.