Continuous monitoring of de-energized loads and conductors

Offline Monitoring

Continuous monitoring of de-energized loads and conductors

Many types of loads that are temporarily or mainly disconnected (standby mode) must function reliably when needed. This applies, for example, to fire pumps, slide-valve drives, lift motors, or emergency power generators.

However, ground faults may occur at the supply line or at the load itself due to humidity or other impacts during prolonged downtimes. If these ground faults are not detected, the protective device triggers and operation is not possible when connecting the installation. In more severe cases, engine fires may occur.

"Offline monitors" can prevent this since they monitor the insulation resistance of de-energized loads in order to report faults at an early stage. Special ISOMETER®s (IR420-D6, IR425-D6, IRDH, iso685 series) are used for this purpose. For this solution, it is irrelevant whether the temporarily or mainly disconnected loads are supplied by grounded or ungrounded systems.

If the insulation resistance between the disconnected load and ground falls below the set response values, the alarm relays switch and the alarm LEDs light up. Monitoring the generator grounding status and leakage values can prevent issues and allow better generator availability during emergencies. The measured value is indicated on the internal display. Therefore, changes that may occur over time or that depend on specific environmental conditions are easily detectable.

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Areas of application


2020 Guidelines (US) Technical Information 1.9 MB EN2020/06/1515.06.2020


DIN 14687-1

Firefighting and fire protection - Permanently installed generator (generating set) < 12 kVA for the use in firefighting vehicles

DIN 14686

Firefighting and fire protection - Switch cabinet for fixed generators (generating set) ≥ 12 kVA in fire-brigade vehicles