Insulation monitoring

Insulation monitoring refers to the permanent monitoring of the insulation resistance of an electrical network with an isolated neutral, in line with the IT-system requirements of the NF C 15-100 standard. Socomec's ISOM range of insulation monitoring devices (IMDs) and the ISOM Digiware L-60/F-60/D-x5 modules measure this resistance in real time and trigger an alarm as soon as a first fault appears. OhmScanner technology locates the fault by monitored outgoing circuit, making preventive intervention easier with no interruption to continuity of service.

Operation of Socomec ISOM insulation monitoring systems

IMD principle on an isolated-neutral network

On an IT network, the first insulation fault does not cause any automatic shutdown of the installation. The insulation monitoring device injects a measurement voltage between the network and earth to continuously assess overall insulation resistance. Our installation feedback confirms that this continuous monitoring detects degradation before it reaches the critical danger threshold.

Fault location by outgoing circuit with OhmScanner

OhmScanner technology combines the IMD with detection tori installed on each outgoing circuit. When an abnormal insulation resistance appears, the system identifies the circuit concerned with no need for a shutdown. Our installation experience shows that this per-circuit location significantly reduces diagnosis time in data centres and operating theatres.

Ranges and modules available for insulation monitoring

ISOM IMD and ISOM Digiware L-60, F-60, D-x5 modules

The ISOM range includes standalone insulation monitoring devices as well as modules compatible with the Digiware bus. The L-60 and F-60 modules provide the measurement and location functions respectively, while the D-x5 modules extend communication capabilities. Our standard practice favours Digiware integration when insulation monitoring needs to fit into a centralised measurement and control architecture.

ISOM FP-60 portable locator and torus accessories

The portable ISOM FP-60 fault locator complements the fixed installation by allowing manual fault-finding on site. The associated detection tori, with a polyamide finish, install on DIN rail in the electrical panel. We observe that this combination of fixed and portable tools provides complete insulation-diagnosis coverage.

Standards and compliance for insulation monitoring

Normative references IEC 61557-8 and IEC 61557-9

Insulation monitoring devices are subject to the IEC 61557-8 standard, which defines the requirements for measuring insulation resistance. Fault location, for its part, complies with IEC 61557-9. These two standards guarantee measurement accuracy and alarm-signal reliability under varying operating conditions.

Regulatory application under NF C 15-100

The NF C 15-100 standard requires the IT system and permanent insulation monitoring in healthcare facilities for hazardous locations, as well as in installations where continuity of service is a major constraint. Feedback from design offices confirms that this requirement systematically applies to operating theatres and intensive-care units.

Typical applications and field experience

Continuity of service in critical installations

Insulation monitoring is mainly used in hospitals, data centres and continuous industrial processes. In these contexts, an unplanned shutdown would have major financial or health consequences. Our installation feedback shows that the IT system combined with a high-performance IMD is the technical solution chosen whenever downtime is unacceptable.

Preventive maintenance and reduced downtime

Early detection of insulation degradation turns corrective intervention into preventive intervention. The operator has the time needed to plan the repair during a maintenance window. In the field, we find that this approach reduces unplanned failures by more than sixty per cent in installations fitted with per-circuit location.

Frequently asked questions

What is the difference between an IT network and a TN-S network for insulation monitoring?

The IT network (isolated neutral) allows the first insulation fault without a shutdown and requires permanent insulation monitoring for safety. The TN-S network (earthed neutral) trips protection as soon as the first fault occurs and does not require an IMD.

Can ISOM insulation monitoring be integrated into an existing supervision system?

ISOM Digiware modules communicate natively on the Digiware bus, allowing their integration into a centralised measurement architecture. Insulation-fault information thus becomes remotely accessible on the building management system.

When should the ISOM FP-60 portable locator be used rather than fixed per-circuit location?

The fixed per-circuit locator (OhmScanner) suits installations with a limited, stable number of circuits to monitor. The portable FP-60 is relevant for occasional extensions, temporary networks or where the outgoing-circuit configuration changes frequently.

Are ISOM detection tori compatible with all cable types?

The tori associated with ISOM systems adapt to the conductor sections commonly found in low-voltage distribution. Their DIN-rail fixing standardises their installation in electrical panels regardless of the manufacturer of the surrounding modular devices.