Originally posted by: 2112elec
hi guys, I would like some info on MCCBs. I have looked in the product catalogues but none answer what I am after.
1) could someone give a scenario where the ground fault pick up function is used.
Typically on the larger 630A and above where you have an upstream device (ACB) with un-restricted earth fault protection that you need to grade with. Parallel cable runs may also need the 'RCD' element to trip the larger devices especially on longer cable runs.
2) I cannot find a tripping time if this function is used (on any make)
If it is instantaneous does this mean 0.1, or 0.2 etc
The tripping characteristic is typically a 'definite time' characteristic that can be time delayed from 0.1 to 0.4 seconds on some of the larger devices.Instantaneous is faster than 0.1, you're down at the 0.01sec time delay for instantaneous
3) I have seen the ground fault used where the 5 second disconnection time could not be achieved due to high Ze. Is this a correct use of this function?
The Neutral-Phase, Phase-Phase fault current still needs to meet the Ze of the device without the RCD element. If the Ze is high for 'earth fault' it may be high for the phase-neutral faults too.