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Topic Title: RCD as main switch.
Topic Summary: Tripping
Created On: 29 January 2013 01:47 PM
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 29 January 2013 01:47 PM
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mikejumper

Posts: 1751
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Went to look at a nuisance tripping problem this moring.
The house was rewired by a NIC registered contractor in 2007.

It's a TT earth.

The CU was is not a split load unit and had a 30mA RCD as a main switch, so power to the whole house was lost when it operated.

It's a fairly large detached 3 bedroom house with a youngish family, so lots of appliances running at the same time. My guess is that it's probably cumulative earth leakage causing the problem as appliances get older.

My question is:
Would it be reasonable to ask the original contractors to come back and fit a suitable CU or alter the existing one to accomodate RCBO's
at the contractors expense on the basis that the existing CU did not comply with guidance in the regs at the time it was installed?

They were charged £5k for the rewire.
 29 January 2013 02:00 PM
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vesuvius

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Good luck getting them to come back from 2007

im sure someone will let me know if this is correct or not

From 1st Jan - 1st July 2008 either standard can be used.

From 1st July 2008 installations should be DESIGNED to the 17th Edition.

If an installation is designed to the 16th but construction overlaps the 1st of July it is no problem.

If the installation is designed before the 1st July and construction does not start until after July, then the installation should comply with the one to which it was designed - i.e. possibly the 16th, regardless of when it gets finished!

If your heading down the descrimination route here id say your not going to get very far. youll probably just get into a whole arguement over the situation and regs.

Edited: 29 January 2013 at 02:09 PM by vesuvius
 29 January 2013 02:04 PM
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mikejumper

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Originally posted by: vesuvius
Good luck getting them to come back from 2007

They're local, still trading and still NIC registered.
 29 January 2013 02:07 PM
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AJJewsbury

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My guess is that it's probably cumulative earth leakage causing the problem as appliances get older.

Guesses aren't much of a leg to stand on. I knew of TT installations of about that size, complete with PCs, Sky boxes and all the usual electronic bits and pieces as well as lots of corroding outside lights and grubby/damp outbuildings, all on a single 30mA RCD and the only times it tripped were either during a thunderstorm or when the local rodent population took a liking to PVC.

Would it be reasonable to ask the original contractors to come back and fit a suitable CU or alter the existing one to accomodate RCBO's
at the contractors expense on the basis that the existing CU did not comply with guidance in the regs at the time it was installed?

You can ask, but I doubt you'll get. I would imagine the argument would be that lots of other places in the area are done that way without problems, it's been perfectly OK for 6 years - a fair test period, and if they wanted something different they could have asked for it at the time (and undoubtedly paid even more).

If I recall correctly, the "usual" arrangement at the time was 100mA S type incomer and 30mA covering all sockets, showers etc. So probably not a huge amount better either in terms of leakage (if from electronics would likely be plugged into sockets so be all covered by a single 30mA RCD still), or discrimination in the case of faults (e.g. a L-PE fault on a lighting circuit would take out the 100mA incomer, so blacking out the entire installation just the same).

I'd suggest working out exactly what's causing the trip first. I suspect a suitable solution will be obvious then.

- Andy.
 29 January 2013 02:45 PM
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vesuvius

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Originally posted by: mikejumper

Originally posted by: vesuvius

Good luck getting them to come back from 2007 [IMG][/IMG]


They're local, still trading and still NIC registered.


yeah but the wiring mustve have been to a reasonable standard to the regualtions at that time. and it must have been in working order for around 5-6 years?
 29 January 2013 03:29 PM
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Jaymack

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Originally posted by: mikejumper
Would it be reasonable to ask the original contractors to come back and fit a suitable CU or alter the existing one to accomodate RCBO's at the contractors expense on the basis that the existing CU did not comply with guidance in the regs at the time it was installed?

What was the date of issue for the E.I.C., assuming that one was issued? How does that compare with the date of the requirement for "2 RCD's"? Were any departures recorded from the then current regulations?

Regards
 29 January 2013 03:50 PM
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AJJewsbury

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How does that compare with the date of the requirement for "2 RCD's"?"

er, what requirement for 2 RCDs? - there's nothing even close to that in BS 7671. (I think the closest I know of is probably the French regs which I think have a specified maximum floor area per RCD, but that's not really relevant)

I think the 2-RCDs solution is purely a convention - mostly driven by CU manufacturers - that started way back when only some circuits needed to be on 30mA RCDs and a desire not to make discrimination any worse. You can read BS 7671 anywhere between one single RCD upfront is fine and every final circuit needs independent RCD protection.

- Andy.
 29 January 2013 05:13 PM
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mikejumper

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Originally posted by: AJJewsbury
You can ask, but I doubt you'll get. I would imagine the argument would be that lots of other places in the area are done that way without problems, it's been perfectly OK for 6 years - a fair test period, and if they wanted something different they could have asked for it at the time (and undoubtedly paid even more).
- Andy.

In this case the customer has no electrical knowledge and employed these guys in good faith, if you know nothing about a subject you don't know the right questions to ask.
I'm sure if they were advised that installing a split load board would minimise disruption when a fault occurred and that this would cost another £50 they would have agreed to it.
 29 January 2013 05:23 PM
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AJJewsbury

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I'm sure if they were advised that installing a split load board would minimise disruption when a fault occurred and that this would cost another £50 they would have agreed to it.

Someone would have been fibbing if that had be so advised though - you'd need an all-RCBO at probably +£400 in those days to minimise disruption (even then there's still room for debate).

Equally they might have been offered a 30mA/100mA-S split board, but been advised of the better shock protection of having all circuits benefiting from 30mA rather than 100mA protection - and gone for that. (17th Ed style boards with 2 separate RCDs plus incomer probably weren't that available in 2007).

I think we're both just guessing...

- Andy.
 29 January 2013 05:24 PM
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OMS

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Our old friend, Arbut Whatif, gets around a bit doesn't he

I think you'll have a sod of a job proving the design isn't compliant with BS 7671 at that time. (or even now - the whole issue of hazard and inconvenience being subjective)

regards

OMS

-------------------------
Failure is always an option
 29 January 2013 06:02 PM
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JZN

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To summarise then I think you need to find out what is causing the tripping.

Before the test gear comes out it will be the usual customer iterrogation about times of day and what's running (to try and rule out dodgy appliances). The obvious stuff like water filled outside sockets and light fittings (had a few of these this year with the wet weather).

Best of luck
John
 29 January 2013 07:04 PM
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daveparry1

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Mike, I think this customer has probably been happy with the installation for the past 5-6 years but now a fault has developed. So along come you and instead of trying to find the fault you have started filling his head with non-existent non-compliances and ideas about getting the original contractor to come along and sort it out for nothing?
You really do sound like a customer talking Mike!

Dave.
 29 January 2013 07:07 PM
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Jaymack

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Originally posted by: AJJewsbury
How does that compare with the date of the requirement for "2 RCD's"?"

er, what requirement for 2 RCDs? - there's nothing even close to that in BS 7671. (I think the closest I know of is probably the French regs which I think have a specified maximum floor area per RCD, but that's not really relevant)

Row and empty hoose syndrome! Of course it's not in the regs, what does "2 RCD's" convey to you?

I think the 2-RCDs solution is purely a convention

But it's desireable for reasons of redundancy!

Regards
 29 January 2013 08:29 PM
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mikejumper

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Originally posted by: daveparry1
Mike, I think this customer has probably been happy with the installation for the past 5-6 years but now a fault has developed.
Dave.

Isn't everyone happy as long as there are no faults however many years it is.
But aren't we supposed to consider when designing an installation
what the situation would be when a fault occurs.
Is losing power to an entire house when a fault occurs good design?
 29 January 2013 08:46 PM
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mikejumper

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Originally posted by: OMS
I think you'll have a sod of a job proving the design isn't compliant with BS 7671 at that time. (or even now - the whole issue of hazard and inconvenience being subjective)
OMS

Have a shufty in the brown OSG pages 20 & 21 if you have it.
This seems to give the preferred options at the time.
 29 January 2013 09:15 PM
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Jaymack

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Originally posted by: mikejumper
But aren't we supposed to consider when designing an installation what the situation would be when a fault occurs. Is losing power to an entire house when a fault occurs good design?


Not if it can be avoided. Picture the actual scenes: -

1. Callout on a Saturday evening, 1 of 2 RCD's had tripped, 6 members of the Glumm family in the living room and can't watch telly ....... No way José. The owner agreed to use a 4 way extension reel on the other circuit, until the Monday.

2. Landlord called on a Saturday morning 2 weeks ago ... same story! But he only wanted it investigated on the Monday, as "there was only one person in the house and he had half the sockets and lights!" That was a faulty Hager RCD that wouldn't reset.

Others have probably had similar experiences to justify inbuilt redundancy. You know it makes sense.

Regards
 29 January 2013 09:28 PM
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slittle

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My previous house had a 30ma incomer 6 way board that I installed when we beat the aussies at rugby in the world cup which was probably around 2000-2001 ?

Never caused a problem other than when the oven element failed.

Don't and never will see a problem with an rcd incomer providing the risks that may be present when the rcd operates can be minimised


Stu
 29 January 2013 09:32 PM
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daveparry1

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Similar here Stu, stand-alone 30m/a front end rcd been in place here for 25 years, never caused any inconvenience, probably only tripped half a dozen times in all, we've had more inconvenience with power cuts i'd say!

Dave.
 29 January 2013 09:46 PM
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colinhaggett

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I always wonder why the owners call a different electrician rather than the firm that carried out the original work. Personally I would find the cause of the fault and advise from their.
 29 January 2013 09:48 PM
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daveparry1

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Same here Colin!
IET » Wiring and the regulations » RCD as main switch.

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