Fuse Blown

Yes, a back EMF is created when the field collapses. While clearing fuses may be unusual, opening the driver transistor is not. A diode is inserted across the coil to dissipate this surge.

Tks JW .

Point noted. will test the installation of the diode.

Before energising the circuit, verify that the cathode of the diode is connected to the positive of the DC supply feeding the relay.

Otherwise either the circuit protective device or the diode will fail catastrophically.

I have experience in a motor circuit that if there is an interruption in the millisecond range, it will not blow the immedaite fuse but will trips the MCB, due to voltage spiking.

i know your question is something else, but this starting statement is intriguing, and if you will pardon me, somewhat wrong.

All tripping is due to current. If there is an interruption in millisecond range, it is due to a short circuit current, which is cleared based on the magnitude of the current, (not voltage) by the MCB. The fuse will blow on longer duration faults, which are not quite short circuits, but higher than overloads certainly (>8xIn). On normal overloads (say up to 8 x In) the overload relay will act, tripping the contactor.

Or maybe i misunderstood your statement, if so, sorry.

Guru,

You are right, I did not phrase it correctly, my experience is with one mixer control, where there is no deadband set in the control circuit which interlock to the weight system. As usual the fluctuation of weight reading trigger the stop and restart almost instantenously and trip the MCB.

This is was realised only after a video camera is use to capture the audio, a double mechanical knock was heard.

Tks Guru.