DOLD AN5873 Insulation Monitor

Core Performance & Industrial Application

The DOLD AN5873 (VARIMETER IMD) monitors the insulation resistance of ungrounded DC and three-phase AC IT systems per IEC/EN 61557-8.

It detects both symmetrical and unsymmetrical insulation faults using a low-frequency alternating measuring voltage injected between line conductors and PE.

The separate auxiliary supply allows monitoring even when the monitored mains is de-energized, with no additional coupling device required.

An LED chain and analog output show the actual ground resistance; on fault the relay trips and the red fault LED lights.

It supports manual or auto reset selection, external reset/test button connection and hysteresis or de-energized-on-trip configuration.

It is widely used as spare replacement in medical IT systems, industrial isolated networks and off-grid DC installations.

Technical Specifications

▶ Product type: Insulation monitoring relay

▶ Brand: DOLD (VARIMETER IMD)

▶ Model: AN5873 (AN5873.11/102)

▶ Monitored system: 3 AC 24 ~ 690 V / DC ≤ 1000 V IT system

▶ Auxiliary supply: AC 230 V (0.8 ~ 1.2 UN, others on request), 40 ~ 400 Hz, ~4 VA

▶ Response value RAN: Fixed 50 kΩ (10 ~ 440 kΩ on request)

▶ Measuring voltage: Approx. ±13 V; max measuring current <0.3 mA

▶ Measuring cycle: 2 ~ 16 s adjustable, factory 2 s

▶ Output: 1 changeover contact, 8 A @ AC 250 V

▶ Analog output: Voltage proportional to insulation resistance

▶ Reset: Built-in reset button; external reset/test option

▶ Operating standard: IEC/EN 61557-8

▶ Mounting: DIN rail, 100 mm module width

▶ Feature: Fault LED chain, manual/auto reset selectable, mains-off monitoring

▶ Country of origin: Germany

▶ Compliance: CE certification

Industry Applications

Applied in medical isolated IT systems, industrial ungrounded power networks, UPS and off-grid DC insulation monitoring spare replacement.

Note: Confirm auxiliary voltage, response threshold and relay contact configuration against the nameplate before ordering