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Topic Title: Max Zs readings.
Topic Summary: Lighting Max Zs readings. Minor Works Certs,
Created On: 18 February 2013 02:56 PM
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 18 February 2013 02:56 PM
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BILLYBOY65

Posts: 35
Joined: 11 May 2011

We are carrying out some remedial work to a retail chain and have to replace emergency lighting fittings that are faulty, these are straight swops normally. We are carrying out MW certs and have instances where the Max Zs has been exceeded for the Overcurrent devices, some are old style type4 and others are standard 60898 C10 breakers. We are recording this information on the MW certs but we are aware that this circuit is not compliant, (although it was not compliant before we altered the circuit), I am not sure where I go with this with regard to informing the client.

Some advice please on this one please.

Cheers

Billy
 18 February 2013 03:10 PM
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Ricicle

Posts: 833
Joined: 23 October 2006

If the metallic parts of the EM light are enclosed within insulating material such as in a bulkhead type light then not too much of an issue as it stands.
If metallic casing accessible then you might need to lean on the client a bit more to get the remedials sorted.
You have not electrically made the circuit any worse, but the circuits purpose is improved as the lights now function IMO.

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Empty barrels make the most noise.
 18 February 2013 03:21 PM
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bpelectric

Posts: 3
Joined: 16 December 2008

If your just replacing the fitting like for like i dont see a need to issue a cert but you could replace the MCB with an RCBO. If memory serve's me right, Check Reg 633.2 Im sure that covers this.
In any case you need to inform the client in writing ASAP
 18 February 2013 07:48 PM
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BILLYBOY65

Posts: 35
Joined: 11 May 2011

Installation of an RCBO is not really an option, these are long runs of Lighting, wired through steel trunking, probably 30 flourescent fittings on the circuit, nuisance tripping would be prevalent.

I realise MW certs are not a requirement but the client has a thing about when we disconnect the earth of an accessory, he requires this tested to prove that it got reconnected and we have left the circuit as safe as it was originally.
 18 February 2013 10:20 PM
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lyledunn

Posts: 600
Joined: 13 August 2003

Max Zs for type D and type 4 mcbs can be derived from their thermal characteristic thus perhaps mitigating your concern. check the curves remembering that 5s disconnection was and may still be a perfectly legitimate and acceptable situation. a wee bit of sup bonding may even let you exceed that limit (providing thermal constraints are met).

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Regards,

Lyle Dunn
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