External Current Sensors

The external Residual Current Sensors are available in 500:1, 1000:1, 2000:1 and 10.000:1 ratio and are limited for the output voltage to max. 27 Vrms. High voltages in the case of loose or broken wires are thus avoided. The Current Sensor measures the residual ground fault current according to the Core Balance principle, in that all the current carrying conductors, including the Neutral wire, are fed through the sensor. Normal Core Balance Transformers are made from 2 possible metal groups, mu-metal or Silicon Iron and have an as low as possible winding count to make sure that a high amplification factor is maintained. Both metals have their drawbacks:

• Both metal groups are not linear and have their largest error in the low current region.
• Mu-metal is very sensitive to low temperatures. Below 0°C most mu-metals stop operating, just when ice deposition is a ground fault hazard.
• The power conversion of Silicon-Iron is poor, so bigger cross-section cores are used. The lower the detection level, the bigger the cross-section has to be.
• Mu-metal is sensitive to lock-up due to DC currents. Over a long time it may restore, but one never knows when and how good the core will perform when needed. A high AC current can restore the correct trip point, at the cost of a system trip.

Modern electronics, with some precautions, can overcome the standard problems with Silicon-Iron materials. The drawbacks of mu-metals are material related and cannot be handled by electronics and are most dangerous to use due to lock-up and low temperature behaviour.

Our state-of-the-art Ground Fault protection devices consisting of Silicon-Iron core material with a small cross-section area to save material and highly integrated electronics makes it possible to have an accurate trip current range from 30 mA to 60 A and a Short Circuit detection of over 160 A using one and the same Current Sensor.

These sensors are compatible with all ground fault relays produced by GFS: DGF7-types, DGF10, DGF100, GFU20 and GFU21.
This includes the products brand labled for Eaton Corp.: D64RPBH13, D64RP14, D64RPBH15, D64RP18, D64RPB30, D64RPB100.

GFS manufactures Current Sensors brand labelled for Eaton Corp. known under the following names: