Single-phase or three-phase: what a sauna heater and a chiller ask of your mains

Short version: a small heater can run on a good single-phase 230 V circuit; larger heaters are normally three-phase 400 V machines, and the data plate says which a given model is. A chiller draws 4 to 16 amps depending on its class and runs on its own circuit. If your board is full, the answer is a new circuit or a new supply, and that is your electrician's and your utility's decision.

The arithmetic

On a single phase at 230 V, current is power divided by voltage. On three phases at 400 V, the current in each phase is power divided by 1.73 times 400. The table is built from the ratings in our catalogue; the chiller figures are approximate electrical draws.

The amps in the table are calculated from the kilowatts at a power factor of 1. A real compressor draws somewhat more, and more again for a moment at start-up, so the data plate of the actual unit decides. A 4 HP chiller is more often a three-phase machine; whether a single-phase version is offered depends on the model.

What a villa board offers, country by country

Standards worth naming in a specification: EN 60335-2-53 for sauna heating appliances and infrared cabins, EN 50160 for the voltage characteristics of public networks, HD 60364-7-702 for electrical installations of swimming pools, and the Low Voltage Directive 2014/35/EU, which covers equipment between 50 and 1,000 V AC.

Three numbers to find before you call the electrician

Three numbers settle most of the argument, and all three are on paper in the house. The first is the contracted power on your electricity bill, in kW or kVA. The second is the rating of the main breaker, printed on its lever, in amps. The third is the spare room in the distribution board: a photograph with the cover off shows an electrician within a minute whether a new circuit fits. Send us the three and we check the loads against them before we draw anything.

When to ask for three-phase

• A cabin of eight seats or more: the heater is 10.5 kW and up.
• Two chillers, or a chiller and a large heater running at the same time.
• A hotel, club or clinic, where the board already carries kitchens, pumps and lighting.
• A long cable run to a deck or garden building, where three phases carry the same power at lower current.

Load management, without gadgets

A villa can often avoid a new supply by sequencing: the heater runs on a timer so it is ready at six, the chiller is on its own circuit, and the two do not both peak at the same moment as the oven and the pool pump. We list the loads of everything in the layout, so your electrician can see the worst case in one table.

Three villas, worked through

1. A Spanish flat at the higher electrification grade, 9,200 W of design power. A 6 kW heater (26 A) leaves 14 A for the oven, the washing machine and the lights. It works with a timer and a habit: no oven during a session. A 4 HP chiller (16 A) cannot run at the same time as the heater without a larger supply.
2. A Portuguese house on a 6.9 kVA single-phase contract. The heater alone is close to 6 kVA, so everything else must be off while it runs. The sensible answer is a step up to 10.35 kVA, which is the single-phase limit for a new installation, or three-phase if the distributor agrees.
3. An Irish house on a standard 12 kVA connection, 52 A. The heater and the chiller together draw about 42 A. That leaves 10 A, so the oven is a decision and a shower is a luxury. A timer on the heater, a chiller on its own circuit and a sequence on paper solve it without a new supply.

A long cable, and the volts it eats

Take a 6 kW heater 40 m from the board on a 6 mm² copper cable. Copper's resistivity is about 0.0175 ohm mm² per metre, so each conductor has about 0.12 ohm; the round trip is 0.23 ohm; at 26 A that drops about 6 V, 2.6 per cent of 230 V. That is acceptable. Double the distance or halve the cable size and the drop doubles or quadruples, and a heater that sees 215 V instead of 230 V makes less than it should. We size the cable for the run, and your electrician confirms it.

What the electrician should give you

1. A dedicated, protected circuit for the heater and another for the chiller, with the right residual-current protection.
2. An isolator at the cabin and at the plant space.
3. A cable sized for the distance as well as the current.
4. A certificate for the work, in the form your country requires.
5. A short note of what the board can still carry.

The loads in the table belong to the chiller systems and the glass-front saunas; Spain, Portugal and Ireland each have a supply note of their own.