1 Tore with 2 identical windings red and blue
Finally a copper winding connected to black bananas: this will be the secondary
The magnetic fields from the 2 primary red and blue will mutually cancel each other
No intensity in the secondary as long as the primaries remain identical
If the intensity of one of the 2 primary is higher, the copper coil will be fed
Currently red and blue wire carry the same intensity to power the bulb
The ammeter connected to the secondary coil displays 0
This toroid acts as a differential transformer. secondary intensity = primary difference
If the second bulb uses the right path, there is still no intensity in the secondary
I assure this time a direct return to the generator, by its 'land' ...
Now 1.06 mA! A fault current is generated!
Here is the simplified principle of the AC Alternative DDR Differential
We will measure the trigger of a true 30 mA DDR
The bulb feeds red / blue. The rope wire is connected to the potentiometer available in green
Its setting changes the resistance between phase (red) and earth (green): the leakage current!
Here is the test setup with a commercially available DDR 30 mA differential
The use of 24 V does not cause any concern because it measures I and not U! Except for test button
The test button produces only 3 mA (1/10 °) at 24 V (1/10 ° of 230 ~ 240 V)
A DDR triggers between I / 2 and nominal I; therefore between 15 mA and 30 mA for this model
The ammeter is connected to the 'ground' return of the generator and ...
... And to the leakage terminal controlled by the potentiometer
It triggered just above 21 mA
It triggers instantly for 22 mA, 22 is between 15 and 30: it works!
Real test under 230 V ~ 50 then 60 Hz to check the test button!