State-of-the-art solutions for electrical fire prevention, beyond the standards

In addition to the requirements of IEC 60364-4-42, some additional preventive measures may be selected to mitigate the risks of electrical fire even more pro-actively.

Earth fault monitoring

Increasing the sensitivity of the protection system will reduce the risk of fire but can also increase the risk of unexpected tripping on disturbance that are not real fault. (See Sensitivity of RCDs to disturbances).

Where balance between sensitivity and continuity of service is challenging, the monitoring of earth fault with no automatic disconnection brings also benefits.

Earth current monitoring and alarming allow:

• Early detection of deterioration of insulation
• Abnormal leakage currents
• Detection of neutral to earth unwanted contact in other place than the dedicated earthing link

Fig. F96 – Exemple of 250 A MCCB with earth leakage measurement and alarming (Compact NSX Micrologic 7.3 E AL)

Fig. F97 – Exemple of external earth leakage monitoring relay

Prevention against fire due to connection issues

One of the leading causes of electrical fires in low-voltage equipment is faulty power connections of cables, busbars, and circuit breakers, particularly when the connections are completed on-site.

A faulty power connection can lead to an increase in electrical contact resistance which, in turn, can induce a thermal runaway, which can turn into a fire ignition if not detected early enough.

Power connection maintenance generally involves inspection (visual, thermographic) and cleaning, on a regular basis (yearly). Or with other specific verification means for withdrawable circuit-breakers and/or functional units, to verify the possible ageing of the withdrawable contacts (surface condition, contact pressure ...).

IEC 60364-5-52 Clause 526 provides general requirements for electrical connections reliability and maintainability to achieve durable electrical continuity.

The regular maintenance (visual inspection, thermography, cleaning, ...) of power connections is good, but does not cover the risk of connection failure between yearly inspections.

Additional / new solutions can provide complementary measures of protection against faulty connections.

Additional / new solutions solutions are being proposed by manufacturers, such as:

• More reliable power connections: connections providing a spring-pressure reserve on cables in the event of thermal dilation, creeping, or loosening as a result of external vibrations, for more reliable connections
• Power distribution systems for LV switchboards, with busbars, distribution blocks, device feeders and other connection accessories designed to simplify the wiring, and coordinated with the switching and pretective devices, for a fully tested solution
• Continuous thermal monitoring of power connections, using thermal sensors, for early detection of faulty connections and alarming
• Cable insulation decomposition sensors, which analyze the air inside the switchboard to detect the presence of different gases and particles which indicate abnormal heating of cable insulation material (PVC / XLPE, EPR), early enough to avoid damage to the cable insulation.

Example of solutions proposed by Schneider Electric

Find below 2 examples of switchboards with additional fire prevention mitigation measures / products related to power connexions.

For more information on electrical fire origins, and the latest solutions to mitigate the risks, download the Electrical Fire Prevention Guide (PDF)

* Temperature sensors installed on each phase of the horizontal-vertical busbar junctions, as well as on the ACB upstream/downstream connections.
* One ambient temperature measurement sensor installed in each column (optionally)

Fig. F98 – Example of high power switchboard equiped with thermal sensors

* One sensor at the top of each column, analyzing gases and particles in the air inside the switchboard

Fig. F99 – Example of LV switchboard equipped with cable insulation decomposition sensors