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Topic Title: RCBO's on lighting Circuits
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Created On: 16 April 2014 10:27 AM
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 16 April 2014 10:27 AM
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Mattysmith1983

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I'm currently looking at College scheme to which there are a large number of classroom areas which will benefit from standard T5 florescent lighting. The wiring method is T&E on cable basket leading to an LCM modules and then flex's off the LCM to each fitting. From experience florescent lighting can cause a fair bit of nuisance tripping. What are peoples thoughts on this can this method? does it justify using standard MCB's or does this type of installation need RCBO's.

Even though the College has what could be classed as a day to day care taker / handy man he cant be classed as a skilled person.
 16 April 2014 10:47 AM
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AJJewsbury

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What's driving the desire for RCDs? Unprotected cables buried in walls, high Zs, circuit also serving a bathroom, local RA... ?
- Andy.
 16 April 2014 11:02 AM
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Mattysmith1983

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The installation method would be driving the need for RCD's
 16 April 2014 11:02 AM
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Parsley

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When I was an apprentice many years ago T&E and college building would never have been mentioned in the same sentence.

The caretaker might not be skilled but he should be instructed by his employer's as per EAW reg 16.

Regards
 16 April 2014 11:16 AM
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Mattysmith1983

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These days its all about cost so T&E installations are becoming more common in buildings.
 16 April 2014 11:24 AM
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AJJewsbury

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The installation method would be driving the need for RCD's

Which bit exactly? If it's just switch drops, you could perhaps use BS 8436 cable or steel conduit for those little bits.
- Andy.
 16 April 2014 11:24 AM
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Mattysmith1983

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For curiosity then i take it this type of installation would need RCBO's if no skilled or instructed persons sere present i.e a typical office building.
 16 April 2014 11:27 AM
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AJJewsbury

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For curiosity then i take it this type of installation would need RCBO's if no skilled or instructed persons sere present i.e a typical office building.

No exactly. BS 7671 only demands RCDs for certain particular situations - usually concealed in walls or feeding general use sockets (subject to the skilled/instructed bit) - or bathrooms or where Zs is high - avoid those and you avoid the need for RCDs.
- Andy.
 16 April 2014 11:28 AM
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Mattysmith1983

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Yeah the switch drops but even the actual cable basket installation doesn't remove the need for RCD's as its not an an enclosed containment system and nor does it provide mechanical protection
 16 April 2014 11:40 AM
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Parsley

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Originally posted by: Mattysmith1983

These days its all about cost so T&E installations are becoming more common in buildings.


Reduced CPC's and high fault currents isn't a good combination, Using type C breakers also needs careful consideration manufacturer's data may be required.
Circuits may also have high Ut values if the Ze is lower than expected.

Regards
 16 April 2014 11:43 AM
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Parsley

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Originally posted by: Mattysmith1983

Yeah the switch drops but even the actual cable basket installation doesn't remove the need for RCD's as its not an an enclosed containment system and nor does it provide mechanical protection


Is the cable basket concealed?

Regards
 16 April 2014 11:52 AM
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peteTLM

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Originally posted by: Parsley

Originally posted by: Mattysmith1983



Yeah the switch drops but even the actual cable basket installation doesn't remove the need for RCD's as its not an an enclosed containment system and nor does it provide mechanical protection




Is the cable basket concealed?



Regards


Do the switch drops in galv conduit (and by default earthed at the switch end).
If its in basket its going to be pretty obvious or in a void of some sort.

T and E in basket isnt great, but unless its running through a welding shop, javelin throwing arena or above a kiln then there isnt a problem.

Only instructed persons are going to be drilling or doing anything to the fabric of the building.

The bigger risk would be being plunged into darkness (em lighting should be there of course).

-------------------------
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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 16 April 2014 11:55 AM
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Mattysmith1983

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No its open in the ceiling void. but clause 522.6.5 would apply.
 16 April 2014 12:04 PM
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Mattysmith1983

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If they didn't install the switch drops in galv conduit then this surely justify RCD's
 16 April 2014 12:13 PM
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AJJewsbury

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No its open in the ceiling void. but clause 522.6.5 would apply.

I think your regs are out of date (at least by numbering) - I take it you mean 522.6.100. Surely you're not running the basket through holes in joists <50mm from the top/bottom are you? (There's no RCD option for ceilings anyhow).

even the actual cable basket installation doesn't remove the need for RCD's as its not an an enclosed containment system and nor does it provide mechanical protection

T&E is a sheathed cable isn't it? In most situations it doesn't need enclosure - it can be just clipped to a surface after all.

- Andy.
 16 April 2014 12:20 PM
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Parsley

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I think Matty means 526.6.100 (v)

That's why I queried if the basket was concealed. No need for RCDs as far as I can see. Good practice would be to install switch drops in Galv conduit as Pete already stated.

Regards
 16 April 2014 02:58 PM
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Mattysmith1983

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Sorry yeah its the old 17th edition Regs
 16 April 2014 03:04 PM
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Mattysmith1983

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So are you both of the opinion If they didn't install the switch drops in galv conduit then they still no need RCD's protection.
 16 April 2014 03:53 PM
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Parsley

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RCD's or steel conduit are not required to comply with BS7671 for this type of building. However the majority of the specs I see ask for steel conduit for concealed cable drops in this type of building.

Regards
 16 April 2014 04:15 PM
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Mattysmith1983

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This purely based on the Instructed persons statement otherwise they would need to comply with clause 522.6.101 and 522.6.103 for it to comply. Sorry if i'm going over old ground here put to say you don't need either RCD's or galv conduit for the switch drops in a partition wall contradicts these clauses.
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