EV Charging Load Calculator — Expansion Demand
Adding chargers to a factory, warehouse or commercial site? Enter each group's electrical input, how many there are and the simultaneity your load management will enforce, plus the load already running at that time. You get the coincident kW and kVA — checked against a limit if you give one.
What this tool estimates
The coincident kW and kVA a charger expansion puts on the supply: each group's electrical input × number × an enforced simultaneity, plus the other load running at the same time — and, if you enter them, the line current and the margin against a limit.
What it cannot decide
- Whether the transformer, LT panel, cables or DISCOM sanctioned load can take it — it compares against a limit you supply; it does not know your limits.
- What simultaneity is safe to plan for — below 100% it must be enforced by load management or justified by measured use.
- Harmonics, phase unbalance from single-phase chargers, earthing and the protection each charger needs.
- The DISCOM's connection terms, any EV tariff or separate metering, or what the Electrical Inspector will require.
Result
The coincident demand exceeds the limit you entered. The options are a lower enforced simultaneity, fewer or smaller chargers, charging outside the site's peak, or more capacity — and the DISCOM sanctioned load may need an enhancement.
You have planned on less than 100% simultaneity. That figure holds only if a load-management system enforces it or measured use justifies it — otherwise use 100%.
| Group | Input each | Chargers | Simultaneity | All at full input | Coincident |
|---|
| Step | Value |
|---|
| Simultaneity | kW | kVA | Against your limit |
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Method version 6 October 2026. A screening estimate, not a design: see the limits below.
How this calculator works — and where it stops
What it calculates
The coincident kW and kVA a charger expansion puts on a site's supply — each group's electrical input × quantity × an enforced simultaneity, plus the other load running at the same time — and, from values you enter, the line current and the margin against a capacity limit.
Inputs
- Charger groups. For each: the rating per charger in kW and whether it is the electrical input or the rated output; the efficiency, when it is an output; the number of chargers; and the simultaneity — the share of the group charging at full input at the same moment (0–100%).
- Other coincident load in kW — what already runs on the same supply at the hours the chargers will be busiest. 0 to size the chargers alone.
- Power factor of the combined load (more than 0, at most 1).
- Optional: a capacity limit to check against, in kVA, kW or amps, and the line-to-line supply voltage for a three-phase current.
Method
- Input per charger = the input rating as given, or rated output ÷ efficiency.
- Each group: connected kW = input per charger × number; coincident kW = connected kW × simultaneity.
- Coincident demand (kW) = the groups' coincident kW + the other coincident load.
- Apparent power (kVA) = coincident demand ÷ power factor.
- With a voltage: line current (A) = kVA × 1,000 ÷ (√3 × voltage), for a balanced three-phase load.
- With a limit: margin = limit − demand, compared in the limit's own unit (kVA, kW or amps). A negative margin is shown as an excess, not rounded to zero.
- Sensitivity: the same site with every group at 25%, 50%, 75% and 100% simultaneity.
Assumptions
- An AC charge point passes mains power through to the car's on-board charger, so its rating is close to what it draws from the supply. A DC charger converts inside the unit, so its rated output is less than its input by its efficiency. If a datasheet gives the input in kVA, multiply it by the input power factor on the same datasheet — or ask the supplier for the input in kW.
- Simultaneity below 100% holds only where a load-management system enforces it — capping the group's total input — or where measured use at a comparable site justifies it. Without either, the defensible figure is 100%.
- Chargers draw their full input while charging; the taper as a battery fills is ignored, which keeps the figure on the safe side.
- One power factor applies to the combined load. Loads at different power factors strictly add as kW and kVAr separately, so a single figure is a simplification.
Limitations
- Does not know your limits: the transformer's spare capacity, the sanctioned load or contract demand and the feeder's rating come from you — the tool only compares.
- No harmonics, no phase-unbalance check for single-phase chargers, no cable sizing, earthing or residual-current protection.
- No DISCOM or inspection process: connection terms, any EV tariff or separate metering and load enhancement are for the DISCOM; whether the installation needs the Electrical Inspector's approval under the CEA (Measures relating to Safety and Electric Supply) Regulations, 2023 is for the project to confirm with the inspectorate. The tool applies no clause of either.
- Steady state only, and no standby supply: whether chargers may run on a DG set, and what that does to its sizing, is outside it.
Worked example
Produced by running this calculator with the inputs below.
Inputs
- One group: 4 AC chargers, 22 kW electrical input each, 50% simultaneity enforced by load management
- Other coincident load 20 kW
- Power factor 0.95
- Illustrative checks: a 415 V supply and a 100 kVA limit
Working
- Group coincident kW = 22 × 4 × 50% = 44 kW (88 kW if all four ran at full input).
- Coincident demand = 44 + 20 = 64 kW.
- Apparent power = 64 ÷ 0.95 = 67.37 kVA.
- Line current at 415 V = 67.37 × 1,000 ÷ (√3 × 415) = 93.7 A.
- Margin against the 100 kVA limit = 100 − 67.37 = 32.63 kVA.
Result. 64 kW and 67.37 kVA at PF 0.95 — inside the illustrative 100 kVA limit by 32.63 kVA. With no load management (all four at 100%) the same site needs 108 kW and 113.68 kVA, and the limit is exceeded by 13.68 kVA.
Sensitivity — what moves the answer
- Simultaneity moves the answer most: with every charger at 25% the site needs 42 kW (44.21 kVA); at 75%, 86 kW (90.53 kVA); at 100%, 108 kW (113.68 kVA).
- An output rating mistaken for an input understates the load: if 22 kW were the chargers' output at 94% efficiency, each would draw 23.40 kW and the site 66.81 kW (70.32 kVA).
- Power factor: the same 64 kW is 71.11 kVA at PF 0.90 and 64 kVA at unity.
How engineers use the result
To reserve capacity for chargers at the planning stage, to decide how much load management a site needs before a transformer or sanctioned-load upgrade becomes necessary, and to check a charger supplier's proposal against the site's limits.
When a professional design must replace it
Before ordering chargers or applying for a load enhancement: an electrical engineer confirms the input ratings from the datasheets, the load-management scheme that will enforce the simultaneity, the coincident site demand from logged data, and the feeder, protection, earthing and harmonic effects — together with the DISCOM's connection requirements, the Electrical Inspector's, and any EV-charging provision in the building bye-laws that apply to the site.
Sources
- Apparent power S = P ÷ PF; balanced three-phase line current I = S ÷ (√3 × line voltage) — definitions
- Central Electricity Authority (Measures relating to Safety and Electric Supply) Regulations, 2023 — the safety regulations electrical installations are inspected under; this tool applies no clause — confirm what applies with the Electrical Inspector
Questions people ask before using it
What information do I need before estimating EV charging load?
For each group of chargers: the datasheet's electrical input in kW — or its rated output and efficiency, which the tool converts — and how many there will be; the simultaneity your load-management system will enforce, or 100% if there is none; the other load that runs at the same time as charging, from logged demand at those hours; and the power factor. To check against a limit, the transformer's spare capacity, the headroom under your sanctioned load or contract demand, or the rating of the feeder that will supply the chargers.
Which site conditions could change the EV charging load?
Charging that lines up with the production or air-conditioning peak — fleet vehicles returning at a shift change, for example; a load-management system that is not installed, or not set to enforce the simultaneity you assumed; DC chargers drawing more than their output rating because of conversion losses; single-phase AC chargers unbalancing the phases; harmonics from DC chargers; high ambient temperature derating chargers and cables; and later additions that use the spare capacity you planned around.
What should I send an engineer for a project-specific EV charging review?
The single-line diagram; the charger models and datasheets with their input ratings; a parking layout showing where each charger goes; the load-management scheme you intend to use; logged site demand for the hours vehicles will charge; the DISCOM sanction letter or contract demand; and the transformer and LT panel details. With those an engineer can check the feeder, protection and earthing, and whether the connection needs a load enhancement.
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