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 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.

DB Board Load Calculator South Africa

⚡ Last Updated: May 2026 · SANS 10142-1 Aligned

🗂️ DB Board Load Calculator — Add Your Circuits

Board Type

Single phase = 230V / Three phase = 400V

Main Breaker Size (A) Check your main isolator or Eskom agreement

Diversity Factor (%)

Not all circuits run at full load at once

Circuits on this board

Circuit Name	Breaker (A)	Qty	Phase	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.

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%

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, multiplied by quantity. This gives the installed load. Apply a diversity factor of 50–70% for a realistic maximum demand estimate. SANS 10142-1 requires the main breaker to be rated at or above the maximum demand. This calculator does both steps automatically.

What is phase balance and why does it matter?

Phase balance is how evenly load is distributed across L1, L2 and L3 on a three-phase board. Imbalance causes the neutral conductor to carry current, generates heat, reduces efficiency, and causes equipment problems. SANS 10142-1 recommends keeping phase imbalance below 10%. Distribute heavy loads — geysers, stoves, large appliances — evenly across the three phases when wiring a three-phase board.

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. Eskom typically supplies residential properties with a 60A single-phase or 40A per phase (three-phase) connection. You cannot install a main breaker larger than your supply authority's connection agreement without a formal supply upgrade. If your calculated demand exceeds your current main breaker at a 70% diversity factor, consult a registered electrician about a supply upgrade or load management strategy.

What is a diversity factor and which should I use?

A diversity factor (0–100%) accounts for the fact that not all circuits run simultaneously at full load. For most South African homes, 70% is a realistic working figure. Use 100% (installed load) to assess worst-case demand and verify the main breaker is not undersized. Use 50% for a conservative running-cost or tariff assessment. SANS 10142-1 Table 5 provides diversity factors by building type.

How many circuits can I put on a DB board?

There is no fixed maximum under SANS 10142-1 — it depends on the physical board enclosure size, busbar rating, and total load. Residential boards typically accommodate 8–24 ways. Every circuit needs its own breaker. Earth leakage protection (RCCB or RCBO) is required on socket and bathroom circuits. If you are running out of ways, a sub-board (second DB fed from the main) is the standard solution.

Can I add circuits to my existing DB board myself in South Africa?

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

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DB Board Load Calculator — South Africa

Phase Balance