EngineerHub.orgCan your main fuse support the planned loads?
Basic mode uses a simple existing-load profile and automatically places single-phase loads on the least-loaded phases. Advanced mode accepts measured L1/L2/L3 current, power factor and actual phase assignments. Both modes calculate each phase separately because one phase can overload even when total household kilowatts look acceptable.
How to use this calculator
Select single- or three-phase and enter the main-fuse rating shown by your utility or electrician.
Use Basic mode when you do not have phase measurements. Use Advanced mode for measured L1, L2 and L3 current.
Select the EV charger, heat pump, sauna and any other high-power equipment that may operate at the same time.
Check the limiting phase, the EV charging cap and whether scheduling or dynamic load management is needed.
First time here? Start in Basic mode. The result is intentionally conservative but remains a planning estimate—not permission to alter wiring or protection.
Home supply and appliances
IEC-style 230/400 V household model. Three-phase service is common enough to justify per-phase screening and 11/22 kW AC charger presets.
Single-phase loads are automatically assigned to the least-loaded phases for a best-case planning view.
Example homes
Existing coincident load
EV charger
Heat pump
Electric sauna heater
Other major loads
Add an induction hob, water heater, dryer, second EV charger, workshop machine or another large appliance.
Can the loads run together?
| Phase | Calculated | Planning limit | Spare |
|---|
Recommended next step
Per-phase loading and operating combinations
Each bar is compared with the selected planning limit and main-fuse rating. The scenario table shows whether common combinations fit and the EV charging power that would retain the planning reserve.
Scroll horizontally to view the full phase chart.
| Operating scenario | Highest phase | Planning headroom | Maximum EV setting | Result |
|---|
Regional connection-capacity reference
Approximate nominal active-power capacity before existing household loads, diversity, imbalance or installation constraints.
| Connection | Approximate nominal capacity | Interpretation |
|---|
Worked example: 3 × 32 A European home with an 11 kW EV charger
A step-by-step interpretation of the calculator’s default Continental Europe / IEC scenario.
This example intentionally uses the calculator’s Basic mode so the assumptions are visible. It is a screening case, not an installation design. The household profile is a heuristic starting point; measured phase currents should replace it for a purchasing or service-upgrade decision.
| Load component | L1 | L2 | L3 | How it is obtained |
|---|---|---|---|---|
| Existing household profile | 5.1 A | 6.4 A | 4.8 A | 16%, 20% and 15% of the selected 32 A service rating |
| 11 kW EV charger, 3-phase | 16.0 A | 16.0 A | 16.0 A | I = P /(√3 · 400 V · 0.99) |
| 3 kW heat pump, 3-phase | 4.6 A | 4.6 A | 4.6 A | I = P /(√3 · 400 V · 0.95) |
| 9 kW sauna heater, 3-phase | 13.0 A | 13.0 A | 13.0 A | Resistive load, PF ≈ 1 |
| Calculated simultaneous current | 38.7 A | 40.0 A | 38.4 A | L2 is the limiting phase |
| Nominal service rating | 32.0 A | 32.0 A | 32.0 A | Nameplate comparison only |
| Planning limit with 10% reserve | 28.8 A | 28.8 A | 28.8 A | Calculator planning allowance, not a code requirement |
The EV, heat pump and sauna are all balanced three-phase loads, so each adds current to all three phases. The pre-existing household profile is slightly highest on L2. Adding the full loads raises L2 to about 40.0 A, above both the 28.8 A planning limit and the 32 A service rating.
Before EV charging, L2 already carries about 23.9 A from the assumed household load, heat pump and sauna. Only about 4.9 A remains to the 28.8 A planning limit. Converting that three-phase current back to EV power gives roughly 3.3 kW.
If the only objective were to remain below the nominal 32 A service rating, the same scenario would permit roughly 5.5 kW of EV charging. The calculator deliberately reports the lower value when a planning reserve is applied, leaving some allowance for unlisted and varying loads.
Real household loads rarely stay at every nameplate maximum simultaneously. Before increasing the service size, compare measured high-load phase currents, dynamic EV load management, shifting the sauna or water heating in time, and the actual heat-pump auxiliary-heater behavior.
Background
Engineering basis, equations, assumptions, interpretation and practical limitations for this calculator.
Residential electrical systems are not interchangeable. A European 230/400 V three-phase service, a UK 230 V single-phase service and a North American 120/240 V split-phase service distribute current differently. The preset therefore changes the actual current equations and conductor topology rather than only changing labels.
- Continental Europe / IEC: 230 V line-to-neutral and 400 V line-to-line are used as the default low-voltage household model. Single-phase and balanced three-phase loads are supported.
- UK & Ireland: the same 230 V / 400 V nominal system is used, but single-phase residential service and approximately 7 kW domestic EV charging are emphasized.
- North America: the calculator uses a 120/240 V split-phase model. 120 V loads are assigned to L1 or L2; 240 V loads span both legs and therefore add the same current to each leg.
- Custom: voltage, frequency and topology can be entered directly for screening of other systems.
Single-phase / single-leg current: I = P / (VLN · PF)
Balanced three-phase current: I = P / (√3 · VLL · PF)
North American 240 V split-phase load: I = P / (VLL · PF), with the same current applied to both service legs.
Planning limit: Iplan = Iservice(1 − reserve)
Three-phase loads are treated as balanced. The model is deliberately a current/headroom screen rather than a full dwelling load calculation under any national wiring code.
Model validation note: the equations above are dimensionally consistent when power is entered in watts, voltage in volts and power factor as a ratio. The tool compares conductor current with the selected service limit; it does not calculate thermal cable ampacity or protective-device trip time.
- Confirm the actual service rating. Use the utility agreement, meter documentation, panel/service information or an electrician. Do not open sealed equipment.
- Measure representative simultaneous current. Smart-meter phase/leg data or electrician measurements are much better than annual energy use.
- Use maximum electrical input for major equipment. Include heat-pump backup heaters and other loads that can genuinely overlap with charging.
- Confirm the connection type. A nominal kW rating is not enough; determine whether the equipment is single-phase, three-phase, 120 V leg, or 240 V line-to-line.
- Treat presets as starting points. Service sizes and charger ratings vary by network, property and installation.
Basic-mode household profiles: Low, Typical and High are deliberately simple screening profiles expressed as fractions of the selected service rating. They are not national diversity factors. Their purpose is to let a user explore the tool before measured L1/L2/L3 or split-phase leg currents are available.
Continental Europe: 3.7 and 7.4 kW single-phase charging and 11/22 kW three-phase charging are useful screening presets. Whether a particular charger or current is permitted depends on the local distribution network and installation.
UK & Ireland: the model emphasizes 230 V single-phase domestic charging around 7 kW. Three-phase 400 V charging remains available for properties that actually have a three-phase supply.
North America: 120 V Level 1 and 240 V Level 2 charging are represented. The calculator treats 240 V charging as a load spanning both split-phase legs.
These presets describe electrical topology and common planning cases. They do not determine connector type, installation permission, tariff eligibility or code compliance.
North American code context: EV charging is treated as a continuous load for NEC Article 625 purposes, and service/feeder sizing can involve load calculations and permitted energy-management controls. This calculator intentionally does not reproduce those code calculations; its 120/240 V preset is a conductor-current and headroom model only.
- It does not size conductors, breakers, service equipment or RCD/GFCI protection.
- It does not calculate voltage drop, fault current, short-circuit duty, earthing/grounding, neutral current, harmonics or inrush.
- It does not reproduce country-specific dwelling demand/diversity calculations or utility service-upgrade rules.
- Fuse and breaker operation is not instantaneous at the nameplate current; time-current behavior is outside this model.
- Basic-mode phase/leg placement is a best-case planning arrangement. Actual wiring may be less balanced.
A result of “Fits” therefore means only that the modeled simultaneous current is below the calculator’s selected planning limit. It does not mean that conductor sizing, overcurrent protection, EVSE continuous-load treatment, earthing/grounding, RCD/GFCI protection, utility approval or installation rules have been satisfied.
- IEC 60038 — standard voltages.
- UK Office for Zero Emission Vehicles — residential chargepoint technical specification.
- U.S. Department of Energy — EVGrid Assist charging-level definitions.
- Use the applicable local wiring rules, utility requirements, equipment instructions and qualified electrical-design input for an actual installation.
Frequently Asked Questions
Practical questions about regional systems, service capacity, EV charging and model limitations.
Because household supply topology changes the current calculation. Continental Europe and the UK use IEC-style 230 V / 400 V systems, while North American homes commonly use 120/240 V split-phase service. The calculator changes its conductor model as well as its presets.
It uses 230 V line-to-neutral, 400 V line-to-line and 50 Hz as the default household model. It supports single-phase loads and balanced three-phase loads and emphasizes 11 kW and 22 kW three-phase EV charging as useful screening cases.
The nominal 230 V / 400 V, 50 Hz system remains, but the default household supply is single-phase, service examples emphasize 60 A, 80 A and 100 A, and approximately 7 kW single-phase home charging is emphasized. Three-phase remains available when the property actually has it.
The preset uses 120 V line-to-neutral and 240 V line-to-line. A 120 V load is assigned to L1 or L2. A 240 V load spans both legs, so the same line current is added to each leg. This is different from a European balanced three-phase calculation.
Use Custom when the supply voltage or topology differs from the included regional defaults. Select single-phase, three-phase or split-phase and enter the nominal line-neutral voltage, line-line voltage and frequency.
An 11 kW three-phase charger draws about 16 A per phase at 400 V. Whether it fits depends on the simultaneous household current on every phase. Dynamic load management is often the practical solution.
The charger itself is only part of the service load. Cooking, electric heating, heat pumps, showers and other simultaneous loads can materially reduce headroom. Use measured peak demand where possible and have the installation assessed under the applicable UK requirements.
It is treated as a 120/240 V split-phase service with a 200 A limit on each hot leg. 240 V loads use both legs; 120 V loads can create leg imbalance.
Service protection acts on individual conductors. Single-phase or 120 V loads can concentrate current on one phase or leg even when the total household power appears moderate.
A compatible controller measures household current and reduces or pauses EV charging so the configured service or phase/leg limit is not exceeded.
Not necessarily. Operation depends on current magnitude, duration, temperature and the device time-current characteristic. This calculator compares nominal current only.
No. It is a preliminary planning tool. Actual EV charging and service upgrades require verification of conductors, protection, earthing or grounding, voltage drop, fault levels, equipment requirements and applicable local rules.
They are EngineerHub screening assumptions expressed as fractions of the selected service rating. They are not IEC, BS 7671, NEC or utility diversity factors. Use measured phase or leg current in Advanced mode for a real installation decision.
No. It only means the modeled simultaneous conductor current is below the selected planning limit. Cable sizing, protection, voltage drop, fault current, earthing or grounding, RCD/GFCI requirements, EVSE continuous-load rules and utility approval must be checked separately.