1ph DB Piggy backed off 3ph DB Before Isolator. - EICR

[spinkieieie]

Hi Guys,

This is the second time I've come across this on an EICR, but with slightly different circumstances.
It has made me ponder if my previous code, and if my current idea for coding is correct or not.

Basically someone has bodged an extra single phase supply off the incomer side of a 3 Phase DB Isolator. To me this is bad workmanship and people who do it should recieve a slap..! Surprisingly, they managed to get it to fit without trimming strands off.

Previously scenario it was protected by an MCCB, I coded it a C3, as if the phase it was on tripped on over-current, it would trip the whole MCCB Making the motors, heaters and other accessories on the 3PH db safe. So to me, a C3 seemed legit. Wasn't sure what BS7671 number to put on it.

In this scenario it's protected by a BS88 3PH Switch fuse.
Now i'm thinking this time round, it should be a C2, as if it we're to blow the fuse on OC, the machinery on the rest of the board could go into OC.
Once again, no idea on what reg no to put on it.

Anyone got any feedback or had experience with this?

Cheers,
Steve

 

[Toneyz]

It doesn't sit right with me. what I suppose you have to assess is taking diversity into account are the three phases reasonable balanced and that one of the phases is now overloaded. If a circuit breaker is used all three phases are disconnected if a fault/O.L. happens however a fuse could blow under these circumstances even if the piggyback load was not there

 

[Lucien Nunes]

Yes, it's not so much about how many phases each DB has, or whether the shared submain has linked OCPD, but whether the piggyback load pushes the submain beyond design current. If not, e.g. that phase on the TP+N DB is suitably light, then the problem is an organisational one of the shared submain rather than one of loading. If that phase is now too heavily loaded, it's like any other overloaded DB.

TP loads should be resilient to loss of a phase as this is still a common occurrence despite many circuits having linked OCPD. Supply faults are often one phase down, or one company fuse out. Some are not as well protected as they should be though.