kW, kVA and amps: what connection power do you need
Choosing the right power for your connection is one of the most common sources of confusion for property owners: some ask for too little and end up with fuses that keep “tripping”, while others ask for too much and pay needlessly. In this guide we clarify what kW, kVA and amps mean, how to correctly estimate the power you need, and what you can run on a single-phase or three-phase connection. All values are officially confirmed through the ATR (Technical Connection Approval / aviz tehnic de racordare) issued by Retele Electrice Romania S.A. (formerly E-Distributie Muntenia).
kW, kVA and amps: what each one means
These three quantities describe the same connection from different angles. They are easy to mix up, but each has a clearly defined role.
- kW (kilowatt) – active power. This is the energy your equipment actually converts into light, heat or motion. In practice, kW represents the “real” consumption that you pay for on your bill.
- kVA (kilovolt-ampere) – apparent power. This is the total power the grid must deliver, including the “reactive” part required by motors, pumps and compressors. kVA is the unit in which the approved power is expressed in the ATR.
- Amps (A) – current. This is the quantity that the connection fuse “sees”. If the installation draws more amps than the fuse rating, the fuse trips and you are left without power.
The relationship between them
The link is determined by voltage and by the power factor (cos φ). For an ordinary home, with resistive loads (light bulbs, hobs, water heaters), cos φ is close to 1, so kW ≈ kVA. With motors and industrial equipment, the difference grows.
Indicative formulas:
- Single-phase (230V): kVA = (A × 230) / 1000
- Three-phase (400V): kVA = (A × 400 × √3) / 1000 ≈ A × 0.693
So a single-phase 50A fuse corresponds to a power of around 11.5 kVA, that is approximately 11 kW at cos φ ≈ 1. This is also the typical value of a residential single-phase connection.
How many kW does a single-phase and a three-phase connection have
The question “how many kW for single-phase?” has a practical answer: in everyday use, a single-phase connection provides up to ~11 kW (a typical 50A fuse on 230V). This is enough for most homes that do not have large three-phase loads.
A three-phase (400V) connection generally starts at 11-22 kW and can go well above this, depending on the requirement and on the grid capacity in the area. Three-phase distributes the load across three phases, so it powers high-demand equipment without overloading a single phase.
| Connection type | Voltage | Typical fuse | Indicative power | Suitable for |
|---|---|---|---|---|
| Single-phase | 230V | 25–50A | up to ~11 kW | flats, small/medium houses |
| Three-phase | 400V | 3×20 – 3×32A | ~11–22 kW | large houses, heat pumps, electric cars |
| Industrial three-phase | 400V | 3×40A and above | 25 kW and above | warehouses, workshops, guesthouses |
You can find details and prices for each option on the service pages: single-phase connection and three-phase connection.
How to estimate the power you need
You do not simply add up the power of all appliances, because they never all run at the same time. You use a simultaneity factor (how often they run together). The steps are simple:
- Make a list of the large loads and note the power of each one (in kW).
- Identify what runs simultaneously during a realistic consumption peak (for example: hob + oven + water heater + heating boiler in the evening).
- Add up the peak power and add a 20-30% margin for the future (electric car, extra air conditioning, extension).
- Choose the connection type that covers this requirement.
Example calculation
A house with an induction hob (3.5 kW), oven (2.5 kW), water heater (2 kW), heating boiler + pumps (0.5 kW), lighting and small appliances (1.5 kW) has a realistic peak of ~7-8 kW if they do not all run at once. A single-phase connection of ~11 kW covers this situation comfortably. If you add a 7.4 kW car charger or air conditioning in several rooms, you move towards three-phase.
For a quick, personalised estimate, use the connection cost calculator, which also gives you a price guide depending on type and power.
Table of typical loads and their power
The values below are indicative and help you build your list from step 1.
| Load | Typical power | Recommended type |
|---|---|---|
| LED lighting (whole house) | 0.2–0.5 kW | single-phase |
| Fridge + freezer | 0.3–0.6 kW | single-phase |
| Washing machine | 2.0–2.5 kW | single-phase |
| Electric water heater | 1.5–3.0 kW | single-phase |
| Induction hob (4 zones) | 3.5–7.4 kW | single-/three-phase |
| Electric oven | 2.0–3.5 kW | single-phase |
| Air conditioning (1 unit) | 0.8–1.5 kW | single-phase |
| Heating boiler + small pumps | 0.3–1.0 kW | single-phase |
| Electric car charger | 3.7–22 kW | single-/three-phase |
| Heat pump (house) | 4–12 kW | three-phase |
| Pressure pump / borehole pump | 0.7–2.2 kW | single-/three-phase |
| Welding machine / workshop | 3–10 kW | three-phase |
You will notice that many individual loads are small; the problem appears at peaks and with three-phase equipment (large heat pumps, fast car charging, workshop tools). These push the decision towards three-phase.
When three-phase is mandatory
You switch to three-phase if you find yourself in at least one of these situations:
- Fast car charging (above 7.4 kW) or two electric cars.
- A high-power heat pump for heating/cooling.
- Three-phase equipment from the manufacturer (certain professional hobs, lifts, motors).
- Economic activity – workshop, warehouse, guesthouse, laundry.
- A total requirement that constantly exceeds ~11 kW.
If you already have single-phase and need more power without changing the type, you can request a power upgrade (spor de putere) (from 350 lei in fees, plus the Retele Electrice Romania tariffs). If the requirement grows substantially, the correct solution is to switch to three-phase through a new connection.
How the power is officially set: the role of the ATR
Whatever your own calculations are, the legally approved power is the one stated in the ATR. You declare the requested power in the grid connection (racordare) application, and the operator Retele Electrice Romania checks availability in the grid and issues the approval with the approved power and the connection tariff. This is why the final price of the connection is confirmed through the ATR and cannot be guaranteed on the basis of an estimate alone.
SUN WATT SRL, an ANRE-certified company (execution and design), prepares your dossier, correctly sizes the requested power and assists you throughout the process, including in obtaining the ATR. See the services and indicative prices or write to us directly via the contact page. Phone: 0733 097 440.
Conclusion
Keep the essentials in mind: kW is the real consumption, kVA is the contracted power (the unit in the ATR), and amps are the limit of the connection fuse. For an ordinary home, single-phase of ~11 kW is usually enough; for heat pumps, fast car charging or economic activity, you choose three-phase (400V). Estimate the power starting from the realistic consumption peak, add a 20-30% margin, and confirm everything through the ATR. For personalised figures, use the cost calculator and request a quote.