Unexpected voltage measured - explanation?

Hello everyone,

With my refrigerator, I measured the voltage at the starter device on the back (similar to the one in the attached picture) using a multimeter and noticed strange values.
At 1 and 2, the power cable is connected directly and thus permanent voltage is present; here you measure about 230V, as expected.
At 3 and 4, voltage is present when the relay switches (i.e., when the compressor is supposed to run). When the device is running and you measure here, you get a voltage of over 270V (!)
Even when measuring the voltage (in the switched state) between 4 and 2 or between 1 and 3, you get this value.
How can this be explained?

Regards
N

This is not unexpected but absolutely normal.

It is a Steinmetz connection.

The capacitor creates an auxiliary phase. However, this phase shift is less than 90° instead of 120°. Therefore, only an elliptical rotating field is generated, which is sufficient to set a direction of rotation for the motor, allowing it to start independently. However, this also causes a pulsating torque profile, and depending on the demanded torque, humming noises occur at twice the mains frequency. The capacitor and the motor coil together form a series resonant circuit. During operation, a higher voltage than the mains voltage occurs across the capacitor. To prevent damage, it should be designed for 400…450 V AC, as with the capacitor motor. Due to the capacitor, the currents in the individual branches are different in magnitude. The starting current of the motor depends on the required torque and can be several times the rated current. Since operating larger motors causes increased single-phase loads on the grid, permission to operate motors with Steinmetz connection is limited to 1.5 kW depending on the supplier.

Ah great, thanks for the detailed explanation! This principle was new to me until now - after a bit of googling, it seems that the Steinmetz connection is used to run three-phase motors single-phase. Which in my case is probably the refrigerator compressor. Now this raises another question for me: What happens if you connect another load (not a motor) in parallel at the points I labeled as 3 and 4 using branch terminals, but this load expects 230V? I’m asking because my original plan was to connect a transformer and behind it 12V PC fans here, which should run whenever the compressor is running. I was, of course, impatient and already tried it, and the result is surprising here as well: Although more than 270V appear at the transformer, it still delivers exactly 12.0 V at the output and the fan runs normally... why? Regards N

With what ulterior motive do you want to carry out your experiment?

Without sound knowledge, I wouldn't even approach that in your place. Electricity is deadly. Only trained professionals should handle 230V circuits and for good reason. The Schuko plug was created for laypeople, after that it's the end. Everything beyond that -> trained professional.

Who says that I am an amateur. Can I please get just one answer to my question.