Hello guys,

I will try to summarize my problem as follows

I want to monitor the status (& also remote control) of a UL489 miniature circuit breaker (MCB) in some control panel. The MCB brand is Weidmuller & will be equipped with Shunt trip. The control unit is Beckhoff IPC Cx.

The shunt trip data sheet mentioned that " rated current at 24 vdc is 2A" , "minimum response power 30 VA"
The auxiliary contact data sheet mentioned that " rated current at 24 vdc is 6A"
Beckhoff's Digital input terminals (ELxxxx) mentioned that " rated input current for each channel is 3 mA"
Beckhoff's Digital output terminals (ELxxxx) mentioned that " max output current for each channel is 500 mA"

1) Monitoring : if i wired the NO auxiliary contact to the terminal's channel the drawn current will NEVER be larger than 3 mA , now if the available power supply is 1A 24 vdc ( the power supply will serve other small calculated loads)...It will be enough , correct ? i.e " rated current 6A at 24 Vdc" means maximum "possible" current but won't be necessarily be drawn , if so , why would it need to be that large current it is designed for the purpose of monitoring ?!

2) control : i think i can't wire the shunt trip directly to the DO terminal channel , the min. response power is 30 VA , so Imin = 30 / 24 = 1.25 A hence the terminal can't supply that current & the device won't trip remotely , so i have to use a relay (mechanical or solid state) with different power supply to the relay with ampere higher than 1.25A , correct ?

3) protection : is it a good practice to use some sort of fusing (like 0.5A fuse) for each channel in the Digital input & also digital output terminals? and is i am going to use relays for the Digital output terminals , would i still need fuses or the relay would isolate both parts (input to relay & output of relay ) or should i fuse after the relay output to protect the relay ?

Thank you all in advance & please excuse me for being the first time wiring shut trips & monitoring circuit breakers inside panels.