Fuse monitor boosts motor control safety

ABB had developed a solid-state motor fuse monitor which it asserts is more reliable than electromechanical types and cheaper than previous electronic devices. When a fuse in a three-phase motor control centre blows, the monitor can indicate this both locally and remotely, minimising the danger of two-phase motor loading as well as preventing unsafe neutral voltages.

"Until now," says Jay Gorecha, ABB Control`s product manager in the UK, "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".

He claims that the new OFM monitor is cheap enough to allow routine electronic monitoring in many installations.

The monitor is designed to snap into position on either side of an ABB OS switchfuse, but can also be used with other suppliers` switchfuses and with ABB`s OFAX fusebases. Spade-type connectors are pushed onto each side of the fuselink for each phase.

When the circuit is operating normally, a green LED is illuminated. If a fuse blows, a red LED comes on and the event can be monitored remotely via two auxiliary contacts. These contacts, which can also be used to trigger audible or visual alarms, are galvanically isolated from the power supply so that the control circuit is never connected to the mains, even if there is a short-circuit.

The monitors are available in two versions, spanning voltages of 100-260V AC and 380-690V AC.