MCB / DB Selection Calculator
Screen one circuit or incoming feeder for MCB current rating, then plan distribution-board space independently.
MCB rating check
DB circuit and space planner
| Circuit group | Number of circuits | Actual modules per device |
|---|---|---|
| Lighting (SP example) | ||
| Sockets (SP example) | ||
| AC / dedicated (DP example) | ||
| Other (TP example) |
MCB candidate range: 6, 10, 16, 20, 25, 32, 40, 50 and 63 A. Enter cable capacity after installation, temperature and grouping corrections; an unknown value withholds the candidate. Screening requires Ib ≤ In ≤ Iz and Ib ≤ In × manufacturer derating factor. Factor 1 assumes no derating and must be verified for the actual product and enclosure. Unknown fault current is explicitly unverified; Icn must be checked at the actual supply voltage. Product availability varies.
DB planning counts physical DIN modules, not branded SPN/TPN ways. Default widths and accessory space are editable examples; RCBOs and switched-neutral devices can have different widths. Spare percentage adds outgoing module space and is rounded upward. Example enclosure sizes are 12, 18, 24, 36, 48, 72 and 96 modules. Verify row layout, phase distribution, manufacturer way definitions, busbar rating, enclosure heat limits and accessory compatibility. This planner does not calculate each outgoing circuit’s breaker rating.
Preliminary planning only. A qualified electrical professional must confirm trip curve, inrush, fault disconnection time, short-circuit withstand, selectivity, earthing and required RCD/RCBO protection. MCBs do not replace residual-current protection. Balanced three-phase and electrical input kW are assumed; motor shaft kW and phase imbalance require separate assessment. No automatic diversity or spare-load allowance is applied.
Reference: Schneider Electric: protective scheme criteria.
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Worked example
At 5 kW, 230 V single phase and power factor 0.9, load current is 24.15 A. If corrected cable capacity is explicitly entered as 30 A and breaker derating is 1, the listed current-rating candidate is 25 A. A proposed 6 kA breaking capacity fails if prospective fault current is 10 kA, so selection is blocked. Unknown fault current remains unverified. Independently, the default space plan is 11 outgoing modules + 3 spare + 8 accessory modules = 22, fitting the example 24-module enclosure by space only.