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Topic Title: Theatre Lighting bars
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Created On: 11 July 2013 07:38 PM
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 11 July 2013 07:38 PM
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nottheboy

Posts: 2
Joined: 11 July 2013

I have a project coming up that involves the installation of Internally Wired Bars (IWB's) over a studio/theatre space. Each of these IWB's has 12 (15A round pin) outlets and will be feed via 2.5mm Tri rated cable. To save myself 12 CPC's I will run a single CPC to each of these 12 way bars. However I am coming a bit unstuck with the Adiabic Equation. It only appears to relate to a single protective device. These 12 ways on an IWB go back to a patch bay and ultimately can be all on 1 phase or spread across all 3 depending on how the technician plugs it up. The 12 ways are protected by individual 10A Type C MCB's not a single protective device as the equation works on.

So my question is how to calculate the the correct CSA? Zs of the main DB where the dimmers will be wired into is 0.12ohm. Max PSC of phase to neutral is 2.3kA. I suspect the answer is a 4 or 6mm back from the IWB (where the 12 CPC's and metal work would be commoned to)but that is only through experience of using IWB's not installing them.

Thoughts and comments welcomed as the brain is a bit frazzled today.
 11 July 2013 11:18 PM
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AJJewsbury

Posts: 11679
Joined: 13 August 2003

For common c.p.c.s BS 7671 requires it to be sized for the most onerous circuit - so if you have 12 identical circuits, it would be the same size as you'd use for any one of them. If you like, just assume that only one fault will occur at a time - it doesn't matter which phase etc the other circuits are on or what their protective device is doing, as they're not involved.
- Andy.
 12 July 2013 05:32 AM
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davezawadi

Posts: 2775
Joined: 26 June 2002

The sizing is as Andy says, however I like to fit 2 CPCs, simply because other things may be hung from the bars, and the power may be from other sources than the dimmers. Presumably you are wiring in 1.5 singles in conduit, so two 1.5 CPCs will give a large margin of safety for the other equipment (which is unlikely to be over 5kw in a normal theatre) fed from alternative sources. The extra cost will be trivial. If you are wiring with multicore then it is usual to use 18 core 1.5 cable which has 6 circuits each with its own CPC and which never gives any problem. Remember to IR test your circuits before connecting to the dimmers!

-------------------------
David
CEng etc, don't ask, its a result not a question!
 12 July 2013 12:58 PM
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BigRed

Posts: 558
Joined: 10 November 2006

Indeed, Dave is right here, we installed hundreds of these, we used SY ( with the proper glands!) 1 18 core per 6 circuits and the bar was earthed with a 4mm cable off th ebox at the end of the IWB Watch the length from th edimmers though, wou may have to go up to 2.5mm SY to satisfy the earth loop readings.
 02 August 2013 06:21 PM
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nottheboy

Posts: 2
Joined: 11 July 2013

Thanks for the comments, only just noticed the email notification wasn't switched on and I had failed to see the other posts!
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