Gentlemen,
Thankyou for you input. Since my first post I have been able to confirm that the system within this facility is an IT system. (unearthed neutral)
Given this, we were planning on bringing the three phases and neutral into our system to provide 400v phase to phase and 230v phase to neutral.
Assuming that the 230v loads are somewhat balanced accross all 3 phases I would assume that the neutral would have to be protected since it is ungrounded and therefore considered a current carrying conductor. If fusing was used and in the unlikely event that the neutral fuse blew while the line fuses did not, you would effectively disconnect the neutral from your 230v loads placing in series across two 400v phases. (not good).
Given this I would assume that the proper way to protect this would be to use a 4 pole breaker to assure that all phases and neutral are disconnected when a trip condition occurs.
I have been searching for information regarding this but have been unable to find anything. Does anyone know how or where to verify my line of thinking.
Thanks.
