How does IEC 60364 handle EV charging in maximum demand calculations?

IEC 61851 (EV supply equipment) and the draft IEC 60364-7-722 (EV charging installations) address EV charging infrastructure. The simultaneity factor for multiple EV chargers depends on whether static or dynamic load management is used. Without load management, simultaneity factors of 0.7–1.0 are typical for small numbers of chargers. With smart charging (ISO 15118 or OCPP-based), the simultaneity can be reduced to 0.3–0.5 because the system actively manages charging schedules.

Can I use measured data instead of calculated demand factors?

Yes, and IEC 60364-1 encourages this approach for existing installations being modified. Actual metered demand data over a representative period (at least one year, capturing seasonal peaks) provides the most accurate basis for sizing. The growth allowance should still be applied to the measured peak. For new installations, measured data from comparable buildings in the same climate zone can be used to calibrate simultaneity factors.

How does IEC 60364-8-1 (Energy Efficiency) affect demand calculations?

IEC 60364-8-1 recognises that energy-efficient equipment reduces overall demand. LED lighting (60–70% reduction versus fluorescent), variable speed drives on HVAC (30–50% energy reduction), and high-efficiency motors all reduce the utilization factor for their load category. However, the demand assessment should still be based on the rated power of the installed equipment as the worst case, with efficiency gains reflected in the utilization factor rather than ignored entirely.

Maximum Demand Calculator — IEC 60364 🌍

InternationalEdition IEC 60364-1:2005+A1:2015Free Online Tool

Maximum demand assessment under IEC 60364-1:2005+A1:2015 follows a principles-based framework rather than prescribing rigid demand factor tables. Clause 311.1 requires that the general characteristics of the installation be assessed, including the maximum demand, but the specific numerical factors are intentionally left to national annexes and engineering judgment.

This design philosophy reflects IEC's role as a framework standard adopted by over 80 countries, each with different load profiles, climate conditions, and consumption patterns. The key concepts introduced by IEC 60364 are the simultaneity factor (factor of simultaneous use) and the utilization factor (the ratio of actual demand to rated capacity), which together provide a rigorous mathematical framework for demand estimation.

This calculator implements the IEC methodology using internationally accepted simultaneity and utilization factors with full transparency, allowing engineers in any country to verify the factors against their own national annex requirements and adjust where needed.

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How Maximum Demand Works Under IEC 60364

Framework Principles: Clause 311.1

IEC 60364-1, Clause 311.1 requires the assessment of general characteristics of the installation, including the supply characteristics and the nature of the demand. The clause mandates consideration of:

The maximum demand of the installation as a whole
The number and type of loads and their expected usage patterns
The daily and seasonal variation of demand
Provision for future increases in demand (load growth)

Unlike NEC or AS/NZS 3000, IEC 60364 does not provide specific tables of demand factors within the standard itself. Instead, it establishes two key engineering concepts that form the basis of any demand calculation.

Step 1: Determine Utilization Factor (k_u)

The utilization factor accounts for the fact that equipment rarely operates continuously at its full rated power. It is defined as:

k_u = P_actual / P_rated

Typical utilization factors from IEC guidance and engineering practice:

Electric motors — 0.75 (motors rarely operate at full rated output continuously)
Lighting — 1.0 (lighting is either on or off, minimal partial loading)
Socket outlets — 0.1 to 0.3 (most outlets are unoccupied most of the time)
HVAC systems — 0.8 (cycling between compressor stages)
Industrial process equipment — 0.5 to 0.9 (varies widely by process)

Step 2: Determine Simultaneity Factor (k_s)

The simultaneity factor (also called diversity factor or coincidence factor) accounts for the probability that not all loads will operate at their peak simultaneously. It is defined as:

k_s = P_simultaneous_max / Σ(P_individual_max)

Typical simultaneity factors by load grouping:

Lighting circuits — 0.9 (high simultaneity, especially in commercial buildings)
HVAC systems — 0.8 (multiple units cycling at different times)
Socket outlet circuits — 0.3 to 0.5 (low simultaneity in office environments)
Residential dwellings in a building — 0.4 to 0.8 depending on number of units
Industrial machinery groups — 0.5 to 0.8 depending on process sequencing

Step 3: Calculate Demand at Each Distribution Level

The IEC approach is hierarchical. Maximum demand is calculated at each level of the distribution system, from individual circuits up through sub-distribution boards to the main switchboard:

P_board = k_s × Σ(k_u × P_rated)_per_circuit

At each level, the simultaneity factor may differ. For example, three sub-distribution boards may each have k_s = 0.7, but at the main switchboard level, the simultaneity factor between the three boards might be k_s = 0.8. The overall demand is the product of these cascading factors.

Step 4: Apply Load Growth Allowance

IEC 60364-1, Clause 311.1 explicitly requires consideration of future load growth. Unlike some national standards that ignore growth, the IEC framework treats it as a fundamental design parameter. A typical load growth margin is 20–30% for commercial installations with a 10–15 year design horizon, though this varies by country and building type.

P_design = P_max_demand × (1 + growth_factor)

Step 5: Verify Against Supply Capacity

The calculated maximum demand must be compared against the available supply capacity, considering the reference impedances defined in IEC TR 60725. This technical report provides standardised supply impedance values for different supply types (single-phase, three-phase, LV networks) that are used when the actual supply impedance is not known from the utility.

Step 6: Document per National Annex Requirements

Each country that adopts IEC 60364 publishes a national annex specifying local requirements for demand assessment. For example, the French national annex (NF C 15-100) provides detailed demand tables, while other countries refer to utility planning guides. The designer must identify and apply the relevant national annex for the installation's jurisdiction.

Key Reference Tables

IEC 60364-1, Clause 311.1 — Assessment of General Characteristics

The foundational clause requiring assessment of maximum demand. Specifies that the designer must consider the number and type of loads, their usage patterns, daily and seasonal variations, and provisions for future load growth. Sets the framework for demand assessment without prescribing specific numerical factors.

Referenced as the regulatory basis for performing the maximum demand calculation under any IEC 60364-based national standard. Every demand assessment should cite this clause.

IEC TR 60725 — Reference Impedances and Public Supply Network Impedances

Provides standardised reference impedance values for different supply configurations (single-phase, three-phase, various voltage levels). Used when the actual supply impedance from the utility is not available for verification calculations.

Apply when verifying that the supply can support the calculated maximum demand. Use the reference impedance values for voltage drop and fault current calculations at the point of supply.

Simultaneity Factor Tables (National Annex Dependent)

Each national annex provides specific simultaneity factors for different load types and groupings. These tables translate the IEC framework principle into locally applicable numerical values. For example, the French NF C 15-100 provides detailed k_s values by circuit count and load type.

Select the simultaneity factor for each group of circuits or loads from the applicable national annex. Apply hierarchically from individual circuits up through distribution boards to the main switchboard.

Utilization Factor Guidance (IEC 60364-1 Informative Annex)

Provides indicative utilization factors for common load types: motors (0.75), lighting (1.0), socket outlets (0.1–0.3), HVAC (0.8). These are informative guidance values that may be adjusted based on specific knowledge of the installation's operating conditions.

Apply to each load or load category to account for partial loading and operating duty cycle before applying simultaneity factors at the distribution board level.

IEC 60364-8-1 — Energy Efficiency (Clause 8.3)

Addresses the interaction between energy efficiency measures and demand assessment. Energy-efficient equipment (LED lighting, variable speed drives, high-efficiency motors) may reduce the maximum demand below traditional estimates, but the demand assessment must still cover the worst-case scenario.

Consider when assessing installations with significant energy-efficiency features. Reduced demand should be reflected in the utilization factors but not in the simultaneity factors, which relate to timing rather than magnitude.

IEC 61439-1 — Switchgear and Controlgear Assemblies

Defines rated diversity factor (RDF) for switchgear assemblies, linking the maximum demand calculation to the thermal rating of the switchboard. The switchboard must be thermally rated for the diversified demand, not the full connected load.

After calculating maximum demand, verify that the selected switchboard assembly has a rated diversity factor at least equal to the calculated simultaneity. If RDF is lower than the demand warrants, a higher-rated switchboard or additional cooling is required.

Worked Example — IEC 60364 Maximum Demand

Scenario

A small commercial building with: 50 kW general lighting, 30 kW HVAC (3 × 10 kW split systems), 20 kW socket outlets (40 outlets across 8 circuits), 15 kW miscellaneous fixed equipment (server room UPS, security systems, lifts). Three-phase 400 V supply.

Lighting demand (k_u = 1.0, k_s = 0.9)

Lighting utilization factor is 1.0 (luminaires are either on or off). Simultaneity factor of 0.9 reflects that 90% of circuits will be active during occupied hours — some areas may be unoccupied or using daylight harvesting.

P_lighting = 50 × 1.0 × 0.9 = 45.0 kW

45.0 kW

HVAC demand (k_u = 0.8, k_s = 0.8)

Three 10 kW split systems. Utilization factor of 0.8 accounts for compressor cycling (systems do not run at full capacity continuously). Simultaneity factor of 0.8 reflects that not all zones will demand maximum cooling simultaneously due to solar orientation and occupancy differences.

P_hvac = 30 × 0.8 × 0.8 = 19.2 kW

19.2 kW

Socket outlet demand (k_u = 0.2, k_s = 0.5)

40 socket outlets with 20 kW total connected capacity. Utilization factor of 0.2 reflects that most commercial outlets power monitors and chargers, not high-power equipment. Simultaneity of 0.5 reflects that roughly half of workstations are active at any time.

P_sockets = 20 × 0.2 × 0.5 = 2.0 kW

2.0 kW

Miscellaneous fixed equipment (k_u = 0.9, k_s = 1.0)

Server room UPS, security cameras, fire alarm, and lift motor. These are critical loads with high utilization and are always operational. Simultaneity factor of 1.0 because all systems run continuously.

P_misc = 15 × 0.9 × 1.0 = 13.5 kW

13.5 kW

Subtotal maximum demand (before growth)

Sum all diversified category demands to get the current maximum demand before any load growth allowance.

P_subtotal = 45.0 + 19.2 + 2.0 + 13.5 = 79.7 kW

79.7 kW

Apply load growth allowance (20%)

Per IEC 60364-1 Clause 311.1, a 20% growth margin is applied for this commercial building with a 10-year design horizon. This accounts for additional equipment, tenant fit-out changes, and EV charging infrastructure that may be added.

P_design = 79.7 × 1.20 = 95.6 kW

95.6 kW — equivalent to 138 A at 400 V three-phase (I = P / (√3 × V × PF) with PF = 1.0 for worst case)

The design maximum demand of 95.6 kW (138 A at 400 V three-phase) determines the main incoming cable size, switchboard rating, and transformer capacity. The calculation demonstrates the IEC hierarchical approach: utilization factors reduce individual loads based on operating duty, simultaneity factors reduce grouped loads based on timing probability, and a load growth margin ensures the installation can accommodate future changes without major infrastructure upgrades. The connected load of 115 kW is reduced by 31% through the k_u and k_s factors, demonstrating the cost savings that proper demand assessment provides.

Common Mistakes When Using IEC 60364

1
Assuming that IEC 60364 provides universal demand factor tables that apply in every country. The standard deliberately defers to national annexes for specific numerical factors. An engineer working in multiple countries must identify and apply the correct national annex for each project jurisdiction.
2
Confusing the simultaneity factor (k_s) with the utilization factor (k_u). The utilization factor relates to how heavily each individual load is used relative to its rating. The simultaneity factor relates to the probability that multiple loads will peak at the same time. Both must be applied — they address different phenomena.
3
Ignoring the load growth requirement in Clause 311.1. IEC 60364 explicitly requires consideration of future demand increases. Designing to exactly the current maximum demand with no growth margin violates the standard's intent and results in installations that need expensive upgrades within a few years.
4
Applying residential simultaneity factors to commercial or industrial loads. Commercial buildings with air conditioning have much higher simultaneity than dwellings because the HVAC operates during all occupied hours. Industrial loads depend on process sequencing. Each installation type requires its own analysis.
5
Neglecting to verify the calculated demand against the switchboard's rated diversity factor (RDF) per IEC 61439-1. The switchboard thermal rating must be consistent with the expected diversified load, not just the total connected load or the individual circuit ratings.

How Does IEC 60364 Compare?

IEC 60364 is intentionally the <strong>most flexible</strong> framework for maximum demand assessment. It provides engineering principles (simultaneity factors, utilization factors, load growth) rather than mandatory tables. This makes it suitable for adoption across 80+ countries with vastly different load profiles, but places greater responsibility on the designer to justify the factors used. NEC and AS/NZS 3000, by contrast, remove much of this judgment by providing mandatory demand tables that must be followed exactly.

Frequently Asked Questions

In IEC terminology, the simultaneity factor (k_s) and diversity factor are the same concept: the ratio of the maximum simultaneous demand to the sum of individual maximum demands. Some standards (notably NEC) define diversity factor as the inverse (sum of individual demands divided by maximum demand), which is always greater than 1. IEC 60364 consistently uses the simultaneity factor definition, which is always between 0 and 1.

National annexes specify the actual numerical values for simultaneity and utilization factors. For example, the French NF C 15-100 provides detailed simultaneity factor tables by circuit count (e.g., k_s = 0.9 for 2–3 circuits, 0.8 for 4–5 circuits, decreasing to 0.6 for 10+ circuits). The German DIN VDE 0100 provides different values based on building type. Engineers must identify the applicable national annex for their project location.

No. Clause 311.1 requires that future demand increases be considered, but does not mandate a specific percentage. The load growth allowance is left to engineering judgment based on the building type, expected lifespan, and local experience. Typical values range from 10% for well-defined industrial processes to 30% or more for speculative commercial buildings. Some national annexes provide specific guidance — for example, some specify 25% for office buildings.

Maximum Demand Calculator for Other Standards

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