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Coding muddled circuits

Chris Pearson
This isn't quite what happened ...


You are doing a PIR on a property which has had about three phases of alterations. The householder wants to retain power so that she may use Wifi for her work, so each circuit is locked off individually. Whilst inspecting the downstairs lights, you undo a switch which controls an outdoor luminaire beside a door leading from the dining room to the garden. You get a shock (both literally and figuratively). ?


FI reveals that the lamp was fed from the upstairs lighting circuit.


I think that such a situation is rather dangerous. One might argue that safe isolation should be applied to every accessory, but I think that it would be reasonable for an ordinary person to change a broken switch. It isn't so much a matter of one fault to danger, but one repair to danger.


It also means that if the CU is marked "downstairs lights" and "upstairs lights", the markings are inappropriate.


C2 seems rather extreme - a lot of effort might be required to separate the circuits.

C3 gets my vote.

no code seems reasonable subject to the installation being sound in all other respects.


Interested to hear your views!
Parents
  • 0
    HI Chris


    I'm willing to bet we have all learned the same way - by making mistakes sometimes.


    Small Mistakes. Small mistakes are minor miracles sent to teach us to watch out. (We've all had them)


    Not my way to do things but - Lighting circuits are often run between household floors especially on the stairs and landings. Outside lights can be supplied from either circuit. Sockets; always expect the upstairs/downstairs divide to be violated at some point; if the house holder was refurbishing the lounge umteen years ago - and he/she want to add a socket in the bedroom - maybe it was easier to extend from the ground floor up to the bedroom for example. 


    Isolation of a single circuit with multiple items on that circuit (Such as DSSOs) = don't assume that this item (eg: DSSO) is on the isolated circuit if you cant see every cm of its run......... assume it is on a different circuit.


    And most importantly of all - and the hardest lesson to learn - is watch out for the shared neutral circuit. That'll make a revelation of your thinking. Most especially when you "isolate" a single circuit while leaving other circuits live. 


    A fluke "wand" (a volt stick I think its called) with audible warning is my most recommended bit of check kit for small stuff.


    The end flashes to shows its on and turns solid with an audible beep when it detects an electrical field. (Not be relied on as a sole form of proving dead but useful to back up a very sure assumption - after checking with the ol volt meter of course)


    Even with the DB main switch off, assume that the neighbours house electrics have crept into your property over the last century and wave the wand around before cutting/working on the cabling.


    Certainly if you ever get into a large office kitchen or commercial kitchen, there will be multiple circuits that supply that lot. 


    Kind Regards
Reply
  • 0
    HI Chris


    I'm willing to bet we have all learned the same way - by making mistakes sometimes.


    Small Mistakes. Small mistakes are minor miracles sent to teach us to watch out. (We've all had them)


    Not my way to do things but - Lighting circuits are often run between household floors especially on the stairs and landings. Outside lights can be supplied from either circuit. Sockets; always expect the upstairs/downstairs divide to be violated at some point; if the house holder was refurbishing the lounge umteen years ago - and he/she want to add a socket in the bedroom - maybe it was easier to extend from the ground floor up to the bedroom for example. 


    Isolation of a single circuit with multiple items on that circuit (Such as DSSOs) = don't assume that this item (eg: DSSO) is on the isolated circuit if you cant see every cm of its run......... assume it is on a different circuit.


    And most importantly of all - and the hardest lesson to learn - is watch out for the shared neutral circuit. That'll make a revelation of your thinking. Most especially when you "isolate" a single circuit while leaving other circuits live. 


    A fluke "wand" (a volt stick I think its called) with audible warning is my most recommended bit of check kit for small stuff.


    The end flashes to shows its on and turns solid with an audible beep when it detects an electrical field. (Not be relied on as a sole form of proving dead but useful to back up a very sure assumption - after checking with the ol volt meter of course)


    Even with the DB main switch off, assume that the neighbours house electrics have crept into your property over the last century and wave the wand around before cutting/working on the cabling.


    Certainly if you ever get into a large office kitchen or commercial kitchen, there will be multiple circuits that supply that lot. 


    Kind Regards
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