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Topic Title: Em lighting.
Topic Summary: 400V
Created On: 09 November 2017 01:08 PM
Status: Read Only
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 09 November 2017 01:08 PM
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SKElectrical

Posts: 1122
Joined: 01 February 2009

A while back I started a topic about combined emergency fittings which have their 'switched lives' and 'auxilary lives' supplied from different circuits. I assumed at the time that the sparky had made a mistake.
I now come across installations where the combined emergency fitting is supplied from different DBs (each DB controlled by a contactor). This is intentional.
Any thoughts.
100s of huge installations.
 09 November 2017 01:19 PM
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davezawadi

Posts: 3895
Joined: 26 June 2002

This sounds as though you have a significant shared neutral problem, unless the sections of the fittings have separate N connections.
Assuming that they do, the only difficulty is ensuring isolation for maintenance, probably covered by a warning notice and a lockout procedure. Remember that the neutrals must be separate throughout the final circuit, and of course a connection would trip RCDs and cause unknown current distributions through neutral cables across the installation.

-------------------------
David
BSc CEng MIET
david@ZawadiSoundAndLighting.co.uk
 09 November 2017 02:28 PM
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mapj1

Posts: 9553
Joined: 22 July 2004

3 phase lighting circuits distribute 3 phases and one neutral, but would normally come either from adjacent fuses, or a ganged 3 pole breaker. Actually even without the uncertainty about how the neutral gets back, it sounds like a recipe for the lights going out due to a fault in DB1 and the batteries not being charged to due to the other board having already been off for a week and not noticed.
Not really sure when you would use the contactor to isolate the supposedly permanent supply.
I presume the design authority is unreachable.

-------------------------
regards Mike
 09 November 2017 04:29 PM
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kellyselectric

Posts: 186
Joined: 22 July 2016

This seems totally mad to me surely the emergency lights need to be from the same breaker as the main light then if it trips or the board loses power then the emergency lights come on exactly when they are needed. Think about it thats when they are needed most
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