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!!

 

[grantr37]

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

is that that history woman in your avatar off the TV?

 

[Silly Sausage]

Can't remember her name, but for a blonde, she's quality intellectual -----, love her!
Give me a raven haired big assed lass anytime though!!!

 

[grantr37]

and the point about the picture is that the woman who does the history documentary stuff on TV is well fit....as is the tally-ho bird off the crabbies ginger beer advert and her who was in foyles war n all that ....

don't get me wrong, Lilly cole etc= whoah, but geeky bird would deffo.....

I do say....spiffingly good...I should say....

 

[funkymonkeytwo]

Seems very odd have never come across that before I'd just disconnect a live job done btw what app did you use for your schematic drawing I'm impressed

 

[Engineer54]

Seems very odd have never come across that before I'd just disconnect a live job done btw what app did you use for your schematic drawing I'm impressed

I have, and on my own house in Cyprus too!! lol!! The electrician had wired the stair lights with a feed from both CU's!! An obvious mistake, but easily done if not thinking straight on a Monday morning!! lol!! In Cyprus, on most house's of 3 bedrooms and above, they install an additional CU on the landing for the upstairs power/lighting... (And my house is on a 3 phase supply, as are both the CU's!!)

And another reason why i don't like to see 2 CU's in a standard sized property....

 

[MDJ]

The only time I have seen anything like that is in TSB Banks probably 20 years ago where some special circuits are fed by essential and non essential supplies, but the switching arrangement was catered for this, when one supply was killed the other then took over but control gear was in place to stop back feeding, I didn't get too involved with it as I was helping another spark on the job at the time not running the job, that set up you have shown Sintra is dangerous by the look of it and needs disconnecting from one board, it looks strange for sure, is there anything else connected before the switch on one of the feeds?

 

[Sintra]

No mate straight from the 2 MCB's to the switch. Guys have been tracing out all the lighting circuits on one floor this weekend and they are all fed from 2 MCB's will pop up a wee drawing in a few minutes.

 

[Sintra]

Here is a schematic of the wiring layout

 

[snowhead]

That looks to be intentional.
A fail safe back up for the wiring installation, with no switching between the 2 required.

It must be a Hospital or High security building, Prison maybe??

If it's not the U.K it must be permitted and must be familiar to persons who normally work on that type of system

 

[Sintra]

Have to meet the premises officer and the facilities manager tomorrow afternoon so hopefully they will be able to shed some light on it.