3 phase power electrical radiators (400V)


live in Sweden and have a bunch of three (3) phase heaters at home. Was planning to control these via Z-wave of course but discovered they are 380V/400V. I believe they use 2 power lines instead of one.
Any ideas on how to solve this?

You will have to ask an electrician to confirm, I am just thinking up loud!

If you get a 3phase solid state relais and activate that with a fibaro FGS 221 (3KW), I think that would work.


Just want to make clear; 3 phase-400V is not to play arround with yourself .

Good luck,

Thanks for the input. One idea is also to use a Fibaro 2x1.5kW relay and control the two phases at the same time. Or?

No. Wait, scratch that. Dear god, no.

Some three-phase appliances use all three active wires, sometimes also the neutral. Motors and pumps fall into this category. If you want to turn one of these devices on or off you need to supply or cut power to all three active lines simultaneously. If you don’t then you could damage the appliance. Three Z-Wave switches can’t guarantee that.

Some “three-phase” appliances use the difference between two adjacent 120? phases to provide a single 415 VAC sine wave. Heaters and boilers fall into this category. You could control this with a single relay, but it’d have to be one that is rated to 415 V and it’d have to be happy with both wires being 240 V apart from earth.

Cor’s recommendation of a three-phase solid-state relay is on the money. Get an electrician in and have them install the relay, then you need only worry about tripping the relay with low-voltage DC. Did I mention getting in an electrician?

A three pole relay or contactor with a 240v coil will do this easily.

Use the 3 sets of relay contacts to switch the load (one for each phase wire) and operate the 240v coil which only draws low current from an z wave appliance switch.

The contactor or relay needs to go into a box to keep fingers away, there may be room inside the cool part of the heater for it, if not then some form of enclosure will be needed, make sure it’s earthed if it’s metal.

If you are controlling several of these heaters you can give each one a relay of its own and common all the coil wires so one appliance switch controls them all if you want.


Is the radiotors really 3 phase 400 VAC? In most cases they are connected using 2 separate 230 VAC phases with the brown wire connected to L1 and the blue “neutral” connected to L2. The difference between two 230 VAC phases is 400 VAC.

Anyway, using the Fibaro FG221 Relay Switch there is a possibility using an alternative power supply for the load. Please refer to

and see the “single switch - option with an alternative power supply for the load” image.

Using a cable or wall tube that contains two phases (L1, L2), a true neutral (N) and ground, it would be possible to power the switch with L1 and N, the radiator with L1 and L2 and thus switching the L2. However, I’m neither an electrician nor an experienced user of z-wave switches, so I’m not sure this is safe.

It is rather odd that there are no switches that are capable switching 400 V. There are “heavy duty switches” that are capable switching pretty high currents, but none that is specifically for 400 V.