Hello,


I would say to detect a blown fuse. If a fuse blows, the MCB will trip and that is monitored via aux contacts.


Regards,


Jon

Odd one that.


I hope the MCB has sufficient breaking capacity for the fault currents, also, how are they making the connections to the fuselinks?


Why not just use a 3 phase monitor?

The connections are parallel into the large fuse carrier and then single to the MCB. Very good point maybe a MCB cost less than a 3 phase monitor? We have approximately 10 of these MCC trays that feed our Frequency drives. The first one I saw, I thought there was a mistake so I checked the other trays and got the circuit diagrams to check the circuits, they are all the same. 

I thought I would share this with the community as this is the first time I have come across this.

Hello,


Out of interest, what drives are they connect to? 


Regards,


Jon

Are L1, L2 & L3 permenantly live?


It could be a "pre-charge" circuit, ours used to be internal, we would switch out a high resistance just after the 3ph was applied to the drive, to reduce the magnetising current in the inernal RLC filter etc. as inrush current limiting.

The drives are connected to ABB variable frequency drives of different kW ratings 1.5kW up to 7.5kW about 10 of them each with there own MCB tray.

L1, L2 & L3 are permanently live and connected via the tray to the busbars then through an Isolator to the parallel fuses and MCB down to the drive.


Regards,

Steven