Bender isoUG425-D4-4 Earth Fault Monitor for 12-120 V DC

Earth fault detection for low-voltage DC control and battery supplies

The Bender isoUG425-D4-4 is an ISOMETER for earth fault detection in unearthed DC systems (IT systems) with system voltages of 12 to 120 V. It monitors the asymmetrical insulation resistance RF between the system and earth, measures the system voltage Un (true RMS and DC) with under- and overvoltage detection, and measures the DC residual voltages between L+ and earth and between L- and earth. The maximum permissible system leakage capacitance is 50 uF. The article number of the push-wire terminal version is B71036320.

An important detail from the datasheet: the isoUG425 is not an insulation monitoring device in the sense of IEC 61557-8. It uses a passive measuring method that evaluates the offset voltage produced by a fault on one conductor. Faults that are equally large on both the positive and the negative conductor to earth (symmetrical faults) are not detected. This is why it suits battery-backed DC supplies where a single-conductor fault is the expected case.

Technical specification

Passive measurement and what it means for the application

The isoUG425 measures from a minimum system voltage onwards. Detected faults can be assigned to the alarm relays through the menu, so that K1 may indicate a fault on L+ and K2 on L-, or both relays can be used as pre-warning and alarm. Voltage limits can alarm when the DC system voltage leaves its window. Because it only sees asymmetry, a system with equal leakage on both poles will look healthy; where such symmetrical faults must be detected, an ISOMETER per IEC 61557-8 such as the IR425-D4-2 or iso685-D-P on this site is the right choice. The device can be parameterised from the front or through BMS or Modbus RTU, for example with a COM465IP gateway.

Installation notes

• Connect E and KE separately to PE with the same cross section as the supply terminals A1 and A2.
• Protect the supply with 6 A fuses (5 A for UL and CSA applications); use 60/75 C copper conductors for UL.
• If supplied from the DC system itself, both lines must be fused; below 24 V DC use a separate supply.
• Mount vertically so that the cooling slots are ventilated; an external test/reset button can be connected at T/R.
• The alarm must be audible or visible when the device is inside a control cabinet.

GCC use cases

Typical applications are 24 V, 48 V and 110 V DC control and battery supplies in substations, gas compressor stations and telecom shelters, where a first earth fault must be signalled without tripping. See the relays category for other Bender devices.

Selection and installation notes

Insulation and residual current monitoring devices are selected from the system type (IT, TN or TT), the system voltage, the leakage capacitance and the alarm levels needed. Connect the device to the system and to earth as the manual shows, set the response values from the system design, check the coupling or measuring current transformer and its wiring, and test the alarm and relay outputs after commissioning. Do not do an insulation test of the plant with the monitor connected unless the manual allows it.

Information needed for a quotation

Send the full model code, the quantity, the delivery location in Oman or the GCC, the intended use and any accessories needed, so that the complete package can be quoted together.

Documents and supply information

The manufacturer data sheet is attached to this page and should be read together with the project specification and the site risk assessment before a purchase is confirmed. Ratings, standards and dimensions are quoted as printed on that sheet. Lead time, stock position and certificates available with the shipment are confirmed in the quotation, and we supply to Oman and the wider GCC region for industrial, utility and building services projects.