Really confused

[Sintra]

Came across a very strange circuit set up today and was wondering if anybody had seen anything like it before. I will state now that this is not a UK installation so BS 7671 might not be applicable. OK we have six lighting circuits with 4 fittings per circuit each controlled by a 1 gang 1 way switch (very simple so far). Each circuit is fed via a 15A 3871 MCB but is fed from 2 seperate DB's. For example lighting circuit No. 1 is fed from DB 1 circuit 1L1 and also DB 2 circuit 1L1 and lighting circuit 2 is fed from DB 1 circuit 1L2 and DB 2 circuit 1L2. The neutral for the circuit only comes from DB 1. The circuits are all wired in pvc insulated cable within galvanised conduit and trunking. I have attached a schematic drawing for 1 circuit to try and give a clearer picture of the set up. I hope someone can explain this as it took me about 4 hours today to isolate the damned things as the 2 DB's are not even close to each other and i hadn't got a clue that they were fed from different sources. :mad2:

 

[Deservices]

I can't see the diagram, but only one dis board should be feeding it ,presumably the one that also has the neutral in. Maybe at some point they cut power to one board and temporary fed them from the other board and forget to remove.

 

[Des 56]

My sympathies to you
Not seen anything like that myself,but I can see reasons not to do this

 

[Daibhid]

I would be of the opinion that it may of been from an old emergency backup system, which might of been modernised i.e. originally having a secondary back-up source (Battery or similar) and then if the building underwent a modernisation, instead of tracing all cables, they installed 2 DB's to new supplies and on they went. It doesn't make any other sense to me as it's not practical to have two sources unless one is a back-up in the case of an emergency? Does this help?

 

[Silly Sausage]

A quick glance shows the switch is fed from two sources.
Lose one of them as quickly as possible.

 

[Gage]

Look like an Em. Bodge in case of SM1 Being down or vice versa. Either that or the spark was sadly misinformed on how to wire this bad boy

 

[Sintra]

I would be of the opinion that it may of been from an old emergency backup system, which might of been modernised i.e. originally having a secondary back-up source (Battery or similar) and then if the building underwent a modernisation, instead of tracing all cables, they installed 2 DB's to new supplies and on they went. It doesn't make any other sense to me as it's not practical to have two sources unless one is a back-up in the case of an emergency? Does this help?

That was my original thoughts but both DB's are backed up by a stand by gen set as they originate from the same panel board.

 

[Gage]

That was my original thoughts but both DB's are backed up by stand by a stand by gen set as they originate from the same panel board.

Well on this note I have to go with the 'Helping the circuit out' excuse...story behind this being...at my factory there was a spark who used to put a strand of copper across rewireable fuses to 'Help it out' LOL. No one ever understood his theory before he was so unfortunately made redundant

 

[Sintra]

Lol i like that :lol:

 

[Engineer54]

More likely someone has made a bad mistake during the original installations. I'd just disconnect the feed from the additional supply DB in the switch, and mark it, from where it originates!! lol!!