I have a Multiplus 24/5000/240 and an Autotransformer. According to the Autotransformer manual the Relay is 12 V, and the output voltage of the Multiplus/Quattro is also 12V regardless of the DC Voltage of the Inverter. Here is what it says in the manual
When the Internal ground relay is not selected in VE Config or Victron Connect, there is 12V on the external terminal of the Multi/Quattro for the ground relay control (on all models 12/24/48V this voltage is 12V).
However if I measure the voltage I get the DC Voltage of my system (in my case 27V) and not 12V. I am afraid this will burn out the coils on the Ground Relay in the Autotransformer.