Keep tabs on blown fuses in motor controls

An ABB Automation Tech (LV Products) product story

Edited by the Engineeringtalk editorial team Jul 3, 2000

The new OFM electronic fuse monitor has been developed by ABB Control to provide increased safety and faster repairs for three-phase motor control centres

The new OFM electronic fuse monitor has been developed by ABB Control to provide increased safety and faster repairs for three-phase motor control centres by indicating locally and remotely when a fuse blows.

The unit is a fraction of the price of other electronic fuse monitoring systems, and more reliable than electromechanical types.

The most important application for the OFM fuse monitor will be in complex motor control centres where critical circuits need to be monitored.

Its facility for immediate tripping after a blown fuse will eliminate the danger of 2-phase motor loading as well as preventing unsafe neutral voltages.

The fuse monitor features a compact design which simply snaps into position on either side of ABB's new OS switchfuse, and spade-type connectors are pushed on to each side of the fuse link in each phase.

The device can also be used with ABB's OESA switchfuses or OFAX fusebases as well as other manufacturers' switchfuses.

The unit shows a green LED on the front of the panel when the circuit is functioning correctly and two auxiliary contacts can be used to provide status information to a remote monitoring system, and/or to trigger audible or visual alarms when a fuse blows.

In the case of one or more blown fuses the green LED turns off and a red LED is illuminated.

The OFM fuse monitor is reset automatically after the blown fuse or fuses have been replaced.

Although the unit is powered from the supply upstream of the fuse, the auxiliary contacts are galvanically isolated from the power source so that the mains supply is never connected to the control circuit, even under short-circuit conditions.

The OFM fuse monitor is available in two types; the OFM 260 for voltages between 100 and 260 VAC and the OFM 690 for voltages between 380 and 690 VAC.

According to ABB Control's product manager Jay Gorecha, "Until now, fuse monitoring systems have either been electromechanical devices, using striker pins, which have not proved completely reliable, or they have been too expensive for widespread application.

Our new OFM electronic unit will enable routine circuit monitoring in many applications." ABB Control's new OS switchfuses combine the economy and small size of traditional switchfuses with the safety of a design that shrouds the fuse.

Their higher current and motor power ratings - up to 160A (AC-23) and 90kW (AC-23, 415V) - in compact, DIN-rail or base mounted housings, mean space can be saved in motor control centres and distribution boards.

To give system builders and OEMs maximum design flexibility, OS switchfuses can be mounted either way up, with the switch mechanism between poles if required.

The handle can be mounted on the front or the side of the switchfuse - a useful feature in compact motor control centres where space is at a premium.