Does a DNO 30mA RCD Isolator satisfy 411.4.204 (411.3.2.2)

[jbingham]

IMHO you are worrying about the wrong problem....

Unless this is a really really big property..

which I am guessing it isn't, (as only 4-way wylex box)..

I would be very worried if max Zs for some 60898's cannot be met on a domestic TN-s system?

e.g.  a 6A 60898, type B  Max Zs 7.28..   (table 41.3  pg 62)

so lets minus off 0.8 worth of possible Ze for a TN-S..

that gives us 6.48ohms worth of R1+R2 portion of the Max Zs..      (R1+R2=Zs-Ze)

So 6.48ohms is around 179m of 1.0mm/1.0mm T&E,    

Or  214m of 1.5mm/1.0mm T&E...

{on a lighting circuit}...  

150+ Meters is a BIG domestic lighting circuit!!!

How BIG is this house??

(Do the sums for 16A / 32A  2.5mm & 6.0mm)...?

If you cant get your Zs on a domestic TN-s,  then as Murdoch say's,  it needs FI..

Not a cowboy get out of jail 30ma RCD card!!!!

P.S.

How are you meeting 314.1 (i)  with just a single 30ma upfront RCD?

:C

Agreed..

No need for tin hat IMHO!

Guinness

Testing hasnt been done yet. So far, a lot of time has been spent doing a very thorough visual!  If necessary, FI will be done. 

Did a cowboy write 411.4.204? And did cowboys teach and write the literature for the 2391 course??  

(Using an RCBO on a TN-S if really necessary wasnt my idea to cut corners!)

If prolonged FI, should for example, point to the fault being located buried somewhere that would involve ripping the place to pieces to get to it, and the Zs is just a bit out, then I suppose this would be an example of a circumstance why you may opt to use of an RCBO??

314.1 (i) wont be met (it never has been in this property) because the house was wired with up&down lights into one way, and up&down sockets into one way.  It has been like that since late 60's/early 70's!

 

[Sharpend]

John, it sounds as though you are doing the remedial work as you go? 
the purpose of the EICR is to establish the integrity of the installation for continued use, in the same way an MoT establishes the safety of your vehicle for continued use. 
remedial works are highlighted and are agreed separately usually? Have you agreed to do them as you go, if so how do you price your EICR? Only it sounds as though it’s a small property and you have spent by the sounds of it considerable time doing a visual and have to return to do the testing? I would expect to be able to do a standard 3 bed house comfortably in a day? 

 

[Murdoch]

Testing hasn't been done yet. So far, a lot of time has been spent doing a very thorough visual! 

An EICR is Inspection and Test - that said many inspectors seem to miss out on the inspection part seems sadly lacking

OP - are you getting paid to do this and what is the agreed time scale? 

Just buckle down and do the tests then come back to us

PS - an upfront RCD was often added so that sockets have RCD protection , and probably has absolutely nothing to do with meeting Zs

 

[jbingham]

Thanks for the further replies chaps.

I could spend more time explaining myself, but I came on here hoping to get a straight answer to my question from a few individuals.  Only one person so far has actually done that.

For the purposes of my question, It is irrelevant whos doing the EICR, how much is being charged for works, and how much time is being spent doing it.

The testing will be as thorough as the visuals.  All the work is being done by a competent person.  There are 2 reasons why more time than usual has been spent doing the visuals - but that, again, is irrelevant to my question, and theres no point in going into it because there is no issue regarding that!

Some of my reasons for asking the question was to be able to make contingency plans/plan ahead - in case of such a problem  (if FI exhausted).  But it was also just to actually know the answer to the question.    

Thank you  

 

[jbingham]

PS If you were going to reply:  If a competent person is doing the work then he will know what to do / he will know the answer:

Perhaps he should, but not all competent persons know the answers to everything!

And to give an example, the NIC badged guy whos testing our factory ATM - he understands my question but doesnt know what the answer is - he said he only ever does industrial - never domestic, and would need to consult his boss (if he wanted to).

 

[Fleeting]

PS If you were going to reply:  If a competent person is doing the work then he will know what to do / he will know the answer:

Perhaps he should, but not all competent persons know the answers to everything!

And to give an example, the NIC badged guy whos testing our factory ATM - he understands my question but doesnt know what the answer is - he said he only ever does industrial - never domestic, and would need to consult his boss (if he wanted to).

BS7671 is a document which covers varying types of installation and there is only a few Regulations directly associated with dwellings. Your scenario could and almost certainly is not restricted to a domestic scenario so it could be encountered anywhere, there are commercial sites I attend which have a main rcd switch which are generally historic but it is what it is, as in your case.

 

[Murdoch]

Testing hasnt been done yet. 

you are asking a question that is purely theoretical and with no context, hence why you won’t get a direct answer

 only testing and offering up the results would allow anybody to give a better answer

 it’s that simple

 

[Fleeting]

you are asking a question that is purely theoretical and with no context, hence why you won’t get a direct answer

 only testing and offering up the results would allow anybody to give a better answer

 it’s that simple

Doesn't matter that it is theoretical we can answer the question. The answer is yes providing the requirements of 411.2.204 are met. Testing will give the answers as to whether it is met but he is asking whether a single rcd will comply to 411.2.204 and the answer is yes.

 

[binky]

So what happened to 'nuisance tripping' that precludes the use of a single RCD ? 

As far as I can remember singe rcd main switch went out of favour around 20 years ago. So if I was inspecting an installation over 20 years old, then a single RCD could be deemed 'acceptable' in my opinion, but if someone has stuck an RCD in more recently, for instance, to meet the introduction of RCD protection for all ccts under the 18th edition, then surely this is bad practice? 

 

[Murdoch]

So what happened to 'nuisance tripping' that precludes the use of a single RCD ? 

As far as I can remember singe rcd main switch went out of favour around 20 years ago. So if I was inspecting an installation over 20 years old, then a single RCD could be deemed 'acceptable' in my opinion, but if someone has stuck an RCD in more recently, for instance, to meet the introduction of RCD protection for all ccts under the 18th edition, then surely this is bad practice? 

Surely nobody would be that stupid to do that now?

 

[binky]

Surely nobody would be that stupid to do that now?

 want a bet!  :slap . I've seen several examples of this.

 

[Murdoch]

 want a bet!  :slap . I've seen several examples of this.

Hum - yes - so have I!

One of the recent ones was a house which had a loft extension - the whole house had a 3 way board - with a single up front RCD - and yes they developed a fault so lost everything.

I do think that the 18th should have mandated RCBO's for socket circuits.

 

[kerching]

I have fitted nothing but RCBO boards for about the last 7/10 years at least

i explain the reasoning to the client...if they don't want it then, unless it's exceptional circumstances, I will walk .  Hasn't happened yet

i have yet to see a statistical report on deaths caused by too much protection

just saving

 

[NozSpark]

I do think that the 18th should have mandated RCBO's for socket circuits.

I'd go a step further and say that they should have mandated that circuits should not share RCD protection at all

 

[SPECIAL LOCATION]

I'd go a step further and say that they should have mandated that circuits should not share RCD protection at all

I can sort of understand the logic with 100ma Time delayed TT  RCD's.......

BUT...

30ma RCD, with shared circuits has caused one helluva lot of grief for customers on some faults I was asked to investigate.....

When you factor in one or more days of labour trying to suss-out the cause & fix the problems causing an RCD trip.....

Then using multiple RCBO's to minimise inconvenience actually looks like a  very good bargain!!!!

Of course none of this helps much when 98%+ of customers haven't got a clue what an RCD is or what it does!!!!!!  

Its just another fuse init?????

:C

 

[Murdoch]

I'd go a step further and say that they should have mandated that circuits should not share RCD protection at all

in utopia yes

 

[binky]

I'd go a step further and say that they should have mandated that circuits should not share RCD protection at all

you've just written the 19th edition  :^O