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Topic Title: Emergency Lighting Circuit
Topic Summary: Wiring
Created On: 08 November 2017 09:22 AM
Status: Read Only
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 08 November 2017 09:22 AM
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jorgemilton

Posts: 11
Joined: 17 May 2017

Hello, Good morning
My name is George.

I was testing a emergency lighting circuit at an apartment, three bed, so I found a short between Earth and Neutral.

I suggested to the Project Leader, to run a new leg from the second alarm at the hall to the bed 3 (which is the first point, coming from the DB). Which was a 2 metres cable and there was a little hole to pass the cable.

But he did not like it, he wanted to run a new leg from the second alarm at the hall to the bed 2, which was more complicate because it needs to cut the ceiling, come from a low level to a high lvel, pass through fire proof, 5 metres cable.

I would like to know it my suggestion was correct or not. The circuit is protected by a RCBO, 10A, type B. and the security device was part of the circuit (which is incorrect).

I added a picture, I will hope it works.

https://ibb.co/igednb

Thank you very much for the answers and your time,.
 08 November 2017 10:17 AM
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mapj1

Posts: 9550
Joined: 22 July 2004

What you are really asking is, does a radial circuit have to be a daisy chain, or can it be centre fed, or even a Tree layout.
In general all 3 layouts are OK in most situations.
But some safety critical systems like alarms have a 'line terminator' in the last fitting as part of their self testing, and these can only be wired as simple chains, or the self test fails.
It is not clear from your description if it is the case here.
More generally circuits wired as simple chains are easier to test, having only one far point, and in some cases where the plans are held centrally, there may be a contractual need to stick to the original layout.
So you may be right or wrong.

-------------------------
regards Mike
 08 November 2017 10:20 AM
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AJJewsbury

Posts: 15990
Joined: 13 August 2003

http://ibb.co/igednb

I'd say your suggestion isn't wrong, but it might have some on-going disadvantages. If I've understood correctly your suggestion is to turn a simple radial into a centre-fed radial. In many way's that's better in principle (lower Zs, lower currents, lower voltage drop etc) - but it might have some consequences that your boss might prefer to avoid. Firstly any future routine testing will be more complicated - often testing (R1+R2 and Zs) is just done at the furthest point on a simple radial as that covers all the wiring in one go - in your scenario those tests would have to be done for both end points - so increasing the work. If it's the kind of site that's well documented then your suggestion would also mean a change to the 'as built' records (so that future workers can know what's been done) - which will carry not only the administrative overhead of making the change but also making sure that the now outdated previous version is recalled. Similar situation where there isn't documentation but there are many units (e.g. flats) all done in the same way - having one that's different will trip people up in the future. So you're boss's suggestion - which I think is basically to repair the fault where it is and leave the circuit arrangement unchanged may well be easier/cheaper overall when all the consequences are taken into account.

- Andy.
 08 November 2017 11:58 AM
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jorgemilton

Posts: 11
Joined: 17 May 2017

Can I ask if the link to my picture works?. It only needs copy and paste at any search engine, Google or Yahoo, etc

https://ibb.co/igednb
 08 November 2017 12:11 PM
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ArduinoXR

Posts: 47
Joined: 16 August 2017

Works perfect George. Andy is spot on with his assessment. Because there would essentially be 2no. EOL connections in your design it means more testing, also as-builts would have to be changed to allow for proper testing and efficient fault-finding in future. No harm to be thinking about these things, we all learn something new everyday.
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