DB Board Load Calculator — South Africa

Add up the breaker sizes (in amps) for every circuit on the board. For a single-phase board, the total load is the sum of all circuit breaker ratings. In practice, not all circuits run at full load simultaneously — applying a diversity factor of 50–70% gives a more realistic picture. SANS 10142-1 requires the main breaker to be rated at or above the maximum demand of all circuits combined.

Phase balance refers to how evenly the electrical load is distributed across the three phases (L1, L2, L3) of a three-phase supply. Imbalance causes the neutral conductor to carry current, generates heat in transformers and motors, reduces efficiency and can cause tripping on sensitive equipment. Keeping the three phases as close to equal load as practical is standard good design practice for any residential or commercial board. A well-balanced board distributes similar total loads across all three phases.

The main breaker must be rated at or above the maximum demand of the board. For a house, Eskom typically supplies a 60A or 80A single-phase connection. A main breaker of 60A, 63A or 80A is standard for residential boards. For three-phase supplies, 40A per phase (120A total) is common. The main breaker must also be coordinated with the supply authority's limit — you cannot install a main breaker larger than your municipality's supply rating without upgrading the supply.

A diversity factor accounts for the fact that not all circuits on a DB board run at full load simultaneously. In a home, you rarely use every appliance at once. A diversity factor of 0.5–0.7 (50–70%) is commonly applied to residential boards when calculating maximum demand. This calculator shows the installed load (all breakers at full rating) — apply your own diversity factor to estimate realistic running load. SANS 10142-1's informative annex on assessing estimated load covers this method for different building types; always confirm the applicable factor with a registered electrician for anything beyond a standard residential board.

There is no fixed maximum number of circuits per DB board under SANS 10142-1 — it depends on the physical size of the board enclosure, the busbar rating and the total load. Residential boards typically accommodate 8–24 ways. Each circuit must have its own breaker, and earth leakage protection (RCCB or RCBO) is required on socket and bathroom circuits. A registered electrician must assess whether the existing board can accommodate additional circuits or whether a larger board or sub-board is needed.

No. Under South Africa's Electrical Installation Regulations 2009, all work on a distribution board must be carried out by a registered electrician. The completed installation requires a Certificate of Compliance (CoC), which is mandatory when selling a property. This calculator is a planning and assessment tool only — always use a registered electrician for actual DB board work.

The main DB board (also called the distribution board or consumer unit) is fed directly from the supply meter and contains the main breaker for the whole installation. A sub-distribution board (sub-DB) is fed from a single breaker on the main board and serves a section of the property — common for granny flats, garages, workshops or large homes where running every circuit back to the main board is impractical. Each sub-DB has its own set of circuit breakers, and the feeder breaker on the main board must be sized to carry the total load of everything on the sub-DB.

Surge Protection Devices (SPDs) are strongly recommended and, since the 2024 update to SANS 10142-1, are required on new installations and significant alterations in many circumstances — particularly where sensitive electronics, solar inverters or alarm/security systems are connected. SPDs protect against voltage spikes from lightning strikes (common in South Africa's summer storm regions) and switching surges from the utility grid. An SPD is typically installed at the main DB board, with additional Type 2 devices at sub-boards protecting sensitive equipment. Ask your electrician whether your board has SPD protection — retrofitting is usually straightforward.

A circuit breaker (CB) protects against overload and short-circuit by tripping when current exceeds its rating — it does not protect people. An RCCB (Residual Current Circuit Breaker, sometimes called an earth leakage unit) monitors for current leaking to earth (e.g. through a person or faulty appliance) and trips within milliseconds to prevent electric shock, but provides no overload protection on its own. An RCBO combines both functions — overload, short-circuit AND earth leakage protection — in a single device per circuit. SANS 10142-1 requires earth leakage protection on socket outlets, bathroom circuits and outdoor circuits; RCBOs are increasingly preferred over a single RCCB covering multiple circuits, because a fault on one circuit won't trip every other circuit on the same RCCB.