DB Board Load Calculator — South Africa

Add all circuits on your distribution board, check total load against your main breaker, and verify phase balance for three-phase supplies. SANS 10142-1 aligned.

Quick answer: Total distribution board load is the sum of all circuit breaker ratings on the board. In practice, not every circuit runs at full load simultaneously, so applying a diversity factor of 50–70% gives a more realistic picture of actual demand than simply adding up nameplate breaker sizes (SANS 10142).

⚡ Last Updated: June 2026  ·  SANS 10142-1 Aligned
🗂️ DB Board Load Calculator — Add Your Circuits
Single phase = 230V / Three phase = 400V
Check your main isolator or Eskom agreement
Not all circuits run at full load at once
Circuits on this board
Circuit Name Breaker (A) Qty Total (A)
0A Loading vs main breaker 100%
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Installed Load
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Max Demand (with diversity)
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Apparent Power
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Main Breaker
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% of Main Breaker
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Total Circuits

⚠️ For planning purposes only. All DB board work in SA must be carried out by a registered electrician under SANS 10142. A Certificate of Compliance (CoC) is required.

How to Use This Calculator

Select single or three-phase board type and enter your main breaker size (check the main isolator label or your Eskom/municipal agreement). Choose a diversity factor — 70% is typical for SA homes — then add every circuit on your board with its breaker size, quantity, and (for three-phase) the assigned phase.

Click Calculate to see your installed load, maximum demand, apparent power (kVA), and percentage of main breaker capacity. Three-phase boards also show phase balance — keep imbalance below 10% per SANS 10142-1.

Understanding DB Board Load in South Africa

A distribution board (DB board) is the central point from which all electrical circuits in a building are controlled and protected. Every home and commercial property in South Africa has at least one. The DB board contains circuit breakers for each circuit — lights, plugs, geysers, stoves, pool pumps — and a main breaker or isolator that protects the entire installation from the supply side.

Understanding your board's total load is essential for three reasons. First, safety — an overloaded board trips constantly, causes voltage dips, and creates fire risk if the main breaker is incorrectly sized. Second, planning — before adding a new circuit (air conditioner, electric vehicle charger, solar inverter), you need to know whether your existing main breaker and supply can accommodate the additional load. Third, compliance — SANS 10142-1 requires that the main breaker capacity matches the maximum demand of the installation, and a registered electrician must verify this when issuing a CoC.

How to Calculate DB Board Load — The Formula

Load calculation — SANS 10142-1
Installed Load (A) = Sum of all (Breaker Size × Quantity) Max Demand (A) = Installed Load × Diversity Factor Apparent Power = Max Demand (A) × Voltage (V) ÷ 1000 [kVA] % Loading = (Max Demand ÷ Main Breaker) × 100 Phase Imbalance % = ((Max Phase − Min Phase) ÷ Max Phase) × 100

What is a diversity factor?

Not every circuit runs at full load simultaneously. In a home, you are unlikely to be running the stove, geyser, tumble dryer, pool pump, and all plug circuits at the same time. The diversity factor accounts for this. A factor of 70% means you assume 70% of the installed capacity will be in use at any one moment — a realistic estimate for most South African homes.

SANS 10142-1 Table 5 provides diversity factors for different building types. For residential installations, 0.6–0.7 is typical. For this calculator, 70% is set as the default, but you can adjust it. Always use 100% (installed load) when assessing whether your main breaker is physically capable of handling worst-case demand.

Three-Phase DB Boards — Phase Balance Explained

In a three-phase supply (common in larger homes, townhouse complexes, businesses, and most Eskom commercial connections), the supply is delivered across three conductors — L1, L2, and L3 — each 120° out of phase. Ideally, the load across all three phases should be equal. When it is not, the neutral conductor carries a current proportional to the imbalance, generating heat and wasting energy.

Good practice is to keep phase imbalance below 10%. Above 15–20%, you will notice overheating in the DB board, transformers on the street running hot, and sensitive equipment behaving erratically. When building or modifying a three-phase board, a registered electrician will deliberately balance large loads (geysers, air conditioners, motors) across the three phases.

Common mistake: Putting all heavy single-phase loads (stove, geyser, tumble dryer) on L1 and light loads on L2 and L3. This is a classic cause of phase imbalance. Distribute heavy loads evenly — one geyser on L1, one on L2 if you have two; stove on L3; tumble dryer on L1 or L2.

Common South African DB Board Circuits and Typical Breaker Sizes

  • Lighting circuits: 10A or 16A per circuit, typically 1–4 circuits for a house
  • Plug / socket circuits (15A): 16A or 20A breaker
  • Geyser (3kW): 20A dedicated circuit with double-pole breaker and earth leakage
  • Electric stove / oven: 40A dedicated circuit
  • Pool pump: 16A dedicated circuit
  • Air conditioner (split unit): 16A or 20A per unit
  • Tumble dryer: 16A or 20A dedicated circuit
  • Garage / gate motor: 16A
  • Inverter / solar feed: 32A–63A depending on inverter size
  • EV charger (7kW): 40A dedicated circuit — requires supply upgrade assessment

When Does a DB Board Need to Be Upgraded?

Your DB board needs assessment or upgrading when:

  • The main breaker trips regularly under normal use
  • You want to add a large new load — EV charger, solar inverter, additional geyser, second air conditioner
  • You are selling your property and the existing board has no CoC or is non-compliant
  • The board is older than 20–25 years (outdated technology, no earth leakage protection)
  • Phase imbalance on a three-phase board exceeds 10–15%
  • The installed load (sum of all breakers) exceeds the main breaker rating at any diversity factor above 70%
⚠️ Disclaimer: This calculator is a planning and assessment tool aligned to SANS 10142-1, based on the circuit breaker sizes and diversity factor you enter. It does not replace an inspection by a registered electrician. Actual board capacity depends on enclosure size, busbar rating, supply authority agreement and installation condition. All DB board work in South Africa must be carried out by a registered person, with a Certificate of Compliance (CoC) issued on completion. SA Property Tools accepts no liability for decisions made based on this information.

Frequently Asked Questions

How do I calculate the total load on a DB board in 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.
What is phase balance and why does it matter on a three-phase DB board?
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. SANS 10142-1 recommends keeping phase imbalance below 10% for most installations. A well-balanced board distributes similar total loads across all three phases.
What size main breaker do I need for my DB board?
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.
What is a diversity factor and should I use one?
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 Table 5 provides guidance on diversity factors for different building types.
How many circuits can I put on a DB board in South Africa?
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.
Can I add circuits to my existing DB board myself in South Africa?
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.
What is the difference between a DB board and a sub-distribution board (sub-DB)?
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.
Do I need surge protection (SPD) on my DB board in South Africa?
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.
What is the difference between a circuit breaker, an RCCB and an RCBO?
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.
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