Earth Leakage Protection & Measurement Transformers for Low Voltage.

  • To be used with ELR-B, ELR-3C, D30 and DM30 relays.
  • The transformer and relay assembly sensitivity is fixed by the relay.
  • The toroidal transformer CTD-1/28 is specifically designed for DIN rail mounting.


Tipe Code Core Inner ø Weight(kg.)
CTD – 1/28 41055  – 28 mm 0,2
CT-1 / 35 41060 Closed 35mm 0,2
CT-1 / 60 41065 Closed 60mm 0,3
CT-1 / 80 41070 Closed 80mm 0,5
CT-1 / 110 41075 Closed 110mm 0,5
CT-1 / 160 41080 Closed 160mm 1,4
CT-1 / 210 41085 Closed 210mm 1,5
 CT-1 / 300 41088 Closed 300mm 4,4
 CT-1 / 350 41090 Closed 350mm 4,8
 CT-1 / 400 41092 Closed 270mm 8,3
CTA-1 / 60 41066 Open 60 mm 0,3
CTA-1 / 110 41076 Open 110mm 0,5
CTA-1 / 160 41081 Open 160mm 1,4
CTA-1 / 210 41086 Open 210mm 1,5

Working principles: The toroidal transformer is installed between the source and the load. The system works on the current balance principle. In a correct installation the vector sum of the currents is zero and the relay will not trip.

In case of an insulation fault on the circuit a leakage current flows to earth. Now the vector sum of the current passing through the transformer is not zero, this imbalance is detected by the transformer, which induces a current in the secondary winding which is connected to the relay.

If the fault level is higher than the selected sensitivity, and when the trip time delay has elapsed, the relay trips and actuates on the shunt trip of a circuit breaker or the coil of a contactor interrupting the supply to the load.

The dimensioning of the toroidal transformer depends on the diameter of all active wires (not earth conductors) put through the transformers.

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