Residual current monitors

Unscheduled downtimes of machines and plants mean a considerable cost factor. By early detection of insulation faults DOLD insulation monitors help to prevent failures of electrical equipment and thus ensure a better operating reliability and plant safety.

They are used both in earthed and also non-earthed systems, but differ in their function principle:

In earthed systems (TN systems) DOLD residual current monitors detect fault current with the principle of differential-current measurement and are mainly used to avoid cost-intensive downtimes and to prevent the risk of fire which is latent in the case of slowly evolving insulation faults.

In non-earthed systems (IT systems), the insulation resistance to earth of the system to be monitored is measured. Such systems are secured by insulation monitors the use of them in IT systems is required by law by the norm “Safety of Machinery” DIN EN 60204-1 or DIN VDE 0100-410. Thanks to deliberately kept simple functionality of DOLD’s insulation monitors customers benefit from a considerable cost advantage combined with the high quality standard accustomed from DOLD.

  • Save space thanks to compact design
  • Cost-effective and easy-to-use by kept simple functionality
  • Flexible by extended application range of our insulation monitors for systems up to 500V AC and 1000 Hz, i.e. also application for 400V three-phase systems Monitor DC systems up to 280V without auxiliary voltage
  • Improve efficiency: avoid unscheduled downtimes and data losses
  • Improve operational reliability and safety: monitor also at standstill, no interruption of operation in the case of single-phase-to-earth fault
  • Better fire safety: detect slowly evolving insulation faults, minimize accidental arcs as frequent fire cause, split and separetely monitor systems in fire- and exlosion-prone areas
  • Improve workplace safety: no malfunctions of machinery and systems due to earth faults

Earthed (TN) systems

Non-earthed (IT) systems

Differential-current and insulation monitors are used for early detection of insulation faults in applications where unscheduled downtimes of machinery would have serious consequences.

They are used in earthed systems for reasons of efficiency and protection against fire and accidents, but they are required by law in non-earthed systems for the same reasons according to DIN VDE 0100-410 and DIN EN 60204-1. Applications include:

  • Wood working industry: fire prevention
  • Chemical industry: prevent the interruption of chemical production processes
  • Automotive: prevent downtime of entire production lines if one partial area fails
  • Food industry: prevent consequential losses, e.g. failure of a cooling plant
  • Medical: prevent the failure of live-saving facilities
  • Data processing: prevent data loss in computer centers, data processing equipment and systems
Residual current monitors for earthed systems VARIMETER RCM
Function Type of
ranges [A]
Housing Style:
Width [mm]
Residual current monitor,
Type A
0.01 ... 10;
0.01 ... 30
+ + + + + Distribution board: 35
Switch cabinet: 35
IL 5882, SL 5882
Residual current monitor,
Type A, with integrated transformer
AC; DC pulsating 0.01 ... 10;
0.01 ... 30
+ + + + + Distribution board: 105 IR 5882
Residual current monitor,
Type B
AC; DC 0.01 ... 3 + + + + + Distribution board: 70 RN 5883