Ceramic bottle fuse holder, sudden short to DIN rail (earth)

[sysrq]

Hello...
Anyone had any extended experience with ceramic bottle fuse holders.
Shortly after turning on isolator switch there was phase to ground short between one of fuse terminal metallic parts and DIN rail (35A gL/gG fuses have been taken out to test the correct working order of contactors).
MCB with C32 type curve and 6 sqmm conductors tripped as it should.
Might be due to deterioration of dielectric strength or due to close proximity of live metallic components to DIN rail (tight construction). Replaced it with another C32 MCB (only had limited amount of spare ones available).
Will have to put some dedicated motor protection circuit breaker or C25/C20 MCB since the current transformer is only on one phase conductor and with unknown settings on the analogue PLC input.

 

[Marvo]

Is the circuit supplied by a drive/VFD or is it just standard 3 phase? Any chance of photos?

 

[sysrq]

There is no VFD in this Vecoplan model since it's made in 1994.
Contactors must withstand frequent reversals and stalled/locked motor conditions.
When it's stalled then current goes above 40 Amps till the contactors got disconnected after 5-10 seconds. Then after a while (2-5 seconds) it reverses direction to clear the obstruction and eventually regain normal operation.

Probably will try to attach some photos at some point in the future.