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Discuss Rcbo/Rcd protection in the Electrical Forum area at ElectriciansForums.net

C

cliffed

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The new breed of sparkies think that if the Zs is high,just stick a rcbo/Rcd on that curcuit.
Back 20 years ago there was no way you would do that.
Interesting in the code book by Napit,thus is what it says.
Opinions plz
 

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Aico 3000
J

Julie.

Esteemed
Arms
They are correct.

I don't agree with it, but 531.2.2 specifically allows it.

Personally the circuit should be designed correctly, ensuring the Zs is sufficiently low for standard protection to apply.

I think it would be much better if it was allowed only in the most extreme circumstances, for example on a well designed installation, but where the Ze is higher than would normally be expected.

It shouldn't be used to make a poor design complaint.
 
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pc1966

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I agree 100% with Julie on this point. Relying on the complexity of RCD electronics as your primary protection to me is a high risk (compared to a fuse or MCB that can disconnect on adequate Zs) and the regulations ought to be written to allow it only when there are no reasonable alternatives.
 
C

cliffed

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  • Thread Starter Thread Starter
  • #4
Agree,& from the design to the install there should be no way the circuit would go over the Zs required for safe disconnectoon,
 
P

pc1966

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The classic case is TT where Zs is too high and, while a RCD is not mandatory, it is typically the only means of meeting disconnection times.

High current / long sub-mains can also get close if Ze is at the upper end but often thay have a 5s disconnect time so with a BS88 fuse you can often be OK, also far cheaper than a fancy MCCB / RCD setup!
 
Risteard

Risteard

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Esteemed
Arms
They are correct.
Are they? They suggest a C3 observation, which is not appropriate for a compliant solution.

(In the interests of clarity, I don't like that "solution" either.)
 
J

Julie.

Esteemed
Arms
Are they? They suggest a C3 observation, which is not appropriate for a compliant solution.

(In the interests of clarity, I don't like that "solution" either.)
The they is the younger electricians in that the regs do allow it. Sorry if it appeared I meant codebreakers

As for codebreakers, well there are many points that appear harsh or wrong, I can't remember the wording in codebreakers, but I think the point is slightly different, willing to be corrected, but last I looked at those recommended observations it read like gobbledegook to me!
 
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Dustydazzler

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Esteemed
Arms
i know plenty sparks over the years who no longer even do a ZS tests & just do rcd trip times as according to them the rcd is the be all & end all...
 
BruceBanner

BruceBanner

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I think there is, another reg that states reliance on an Me device for basic protection should not be relied upon, as, they fail over time as all ME devices do. I never have, or will do. Time to dig out the book.
 
Ian1981

Ian1981

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i know plenty sparks over the years who no longer even do a ZS tests & just do rcd trip times as according to them the rcd is the be all & end all...
The Niceic brought out an article in their connections magazine which says the same thing, as long as the cpc is confirmed by continuity (R1+R2) etc and the rcd is checked and it’s effectiveness tested, then it is not necessary to measure Zs as per the regulations.
Circuits without rcd protection requires Zs to be measured by direct measurement or other means.76ED816E-0A58-4CED-B287-01CE05A9F81F.png9F400807-1563-4681-A39A-A245BCF62D54.png
 
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D

Dustydazzler

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Esteemed
Arms
The Niceic brought out an article in their connections magazine which says the same thing, as long as the cpc is confirmed by continuity (R1+R2) etc and the rcd is checked and it’s functionality tested, then it is not necessary to measure Zs as per the regulations.
Circuits without rcd protection requires Zs to be measured by direct measurement or other means.
for years and years one of my jobs as an apprentice was to go round our big job sites and do all the ZS tests (every single plug socket) Once the subby sparks had all moved on to the next site.

now I would only have to test the rcd at the board

where is the fun in that
 

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