Today was a bad day - atleast for me.

In a test rig panel that was due for dispatch next week, a freak accident happened ( a slipped screw driver ) and the 415V ac line shorted momentarily with the +24V dc line and the ELCB tripped in a jiffy. But not before the damage was done.

The following cards serviced by the 24V dc line went dead (smoked):

1. A proportional amplifier card
2. A flowmeter signal conditioner.
3. The 24V dc SMPS

Roughly 1800 USD and lots of confidence and time down the drain.

Fortunatley the whole MCU and I/O cards were serviced by a separate 5V switcher and they survived the incident.

Damage control has started and it is here that I want some advice from the experts who are used to such multi power ( 415V ac, 230V ac, 24V dc and 5V dc )in a single panel.

Is there any way to protect the low voltage circuits ( 5V and 24 V) from such freak shorts ? In my case all the 24V feeders were having proper fast acting fuses - but being thermal elements could not react fast enough. Would zeners or SCRs or transorbs help to control damage ? Is there any method against this madness ?

Thank you guys.

Raghu

PS: I am not too sure if this is on topic - but in my current mind set, felt like discussing with some experts. And no better place than this forum.