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Topic Title: 13amp fused RCD
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Created On: 10 April 2017 03:48 PM
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 17 April 2017 08:09 AM
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alancapon

Posts: 6778
Joined: 27 December 2005

I read that table differently. I understood it to say that fitting an RCD fused spur cannot be used to protect the fixed wiring, which I believe it to refer to the fixed wiring before the fused spur.

Regards,

Alan.
 17 April 2017 08:09 AM
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alancapon

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I read that table differently. I understood it to say that fitting an RCD fused spur cannot be used to protect the fixed wiring, which I believe it to refer to the fixed wiring before the fused spur.

Regards,

Alan.
 17 April 2017 08:09 AM
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alancapon

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I read that table differently. I understood it to say that fitting an RCD fused spur cannot be used to protect the fixed wiring, which I believe it to refer to the fixed wiring before the fused spur.

Regards,

Alan.
 17 April 2017 11:50 AM
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AJJewsbury

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One I'm not religious.

religion as your personal set of beliefs (often based on interpretation of a particular book), rather than organised religion...

Two can anyone confirm that an RCD FCU is suitable for protecting fixed wiring (Beama says not)?

But 30mA RCD protection in bathrooms is for the purpose of providing additional protection (of people from electric shock), not protecting the wiring (in a conventional TN system overcurrent protection devices will do that).

Three, being quite happy with the definition in BS7671, I expect you to always notify and issue an EIC whenever you plug something into a socket.

No, as out of scope of both standards (if wiring downstream of the plug not fixed).

Four if you feel the same level of safety is provided as would be by compliance with the Regulations, then why not just list it as a departure?

Not necessary if it's seen as directly complying.

Yes, this information can be found in the Beama RCD handbook, table 2.
http://www.beama.org.uk/asset/...0-A9ACFBC5C58A94A2/[/q

Interesting table indeed - further up it seems to list FCURCDs as "Suitable as an Outgoing Device on a CU, DB, PB or SB (5,7)" - which would seem to imply (when located directly after the CU) that it can protect an entire circuit - as per Alan's point.

- Andy.
 17 April 2017 01:12 PM
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weirdbeard

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Originally posted by: jcm256

Yes a good suggestion, the consumer unit is old re-wire able RCBO don't fit and no room even to the side or below, I see you are steering me away from fitting RCD in bathroom and will act accordingly.

Thanks.

jcm


I can personally recommend having an upfront 30mA DP RCD in the tails for home use, it would be far safer all round than a token gesture RCDFCU, domestic nuisance tripping is a theory sold by RCBO salespersons

-------------------------
:beer)
 17 April 2017 02:49 PM
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spinlondon

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Andy.
One, you obviously have more knowledge of religion than I do.
I was under the impression that it was a set of cultural beliefs, practices and customs.
As for interpretation, it seems to me that you are the one doing the interpreting, rather than just taking what is stated at face value.
Two, as far as I am aware, the purpose of BS7671 is to protect persons, livestock and property, not just persons.
Then again providing RCD protection to the fixed wiring would help protect persons.
Three, where does it state that the scope of BS7671 only refers to fixed wiring?
Four, seen by who?
BS7671 requires the circuit to be provided with RCD protection, not just part of the circuit.
Compliance with the requirement to protect the circuit, would mean fault current produced by a fault anywhere on the circuit would be detected. Whereas with your suggestion only fault current produced by a fault within the location would be detected.
I see you have swerved answering Five.
So I ask again, why faff around trying to get round the Regs. when compliance is not difficult?

Alan, as no RCD can protect any wiring upstream from where the device is situated, why would you believe that the table is referring only to such wiring?
There is no indication that it is only referring to wiring upstream from the device.
Why not take it as meaning that it cannot protect wiring both upstream and downstream from the device?
 17 April 2017 03:46 PM
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alancapon

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Originally posted by: spinlondon
. . . Alan, as no RCD can protect any wiring upstream from where the device is situated, why would you believe that the table is referring only to such wiring?

There is no indication that it is only referring to wiring upstream from the device.

Why not take it as meaning that it cannot protect wiring both upstream and downstream from the device?

The RCDs job is to protect downstream wiring. I fail to see how it can protect flex connected to its output terminals and refuse to protect t&e connected to the same terminals.

Regards,

Alan.
 17 April 2017 04:21 PM
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spinlondon

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Who knows?
Perhaps it's intended purpose is to protect a single appliance rather than fixed wiring and a number of appliances?
My point being, can anyone confirm that the device is suitable for protecting fixed wiring?
The information in the BEAMA handbook may be incorrect, or it may only apply to some of the 300 manufacturer's products they apparently represent?
Seems that the guide was produced with the help of only a few manufacturers and a few other organisations.
 17 April 2017 05:36 PM
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mapj1

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Interesting document, some good stuff, that bit could probably be clearer. I suppose if you wired it all in flex it would meet the letter of their recommendation, though I'm not really so sure if that was really the intention.
Certainly I have more than once used RCD spurs to protect lights and sockets, in cases where we wanted to add RCD protection to a extant installation, and where having the test and re-set buttons near the point of load made most sense, both in that the test facility would be more likely to be used, and that it makes it far more obvious what has caused any trip, without bringing the whole set up crashing down, and without too much disruption. Admittedly although there was a sink in one case, that was not a domestic bathroom, but the thinking is similar.

-------------------------
regards Mike
 17 April 2017 07:05 PM
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ebee

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Spin.


BS7671 requires the circuit to be provided with RCD protection, not just part of the circuit.


The BS7671 definition of a circuit means after the opd ie the fuse in an RCD FCU makes the outgoing a circuit in its own right.

At least thats the arguement that has been put before.

You would not call the outgoing citcuits of a consumer unit merely part of a circuit because such circuits origininate at the supplyers cut out would you?

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 17 April 2017 08:37 PM
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geoffsd

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Given the definitions we have to work with, I don't disagree with what ebee writes.

So, does that mean an FCURCD would be compliant yet a single RCD in an enclosure may not.



However, I think (because of this and the recent thread regarding Table 52,3) it is time BS7671 had a thorough untangling.
It has been added to and amended so many times without due reference to associated regulations that it is now somewhat of a mess.

That should keep them busy and avoid the need to think up new things just for the sake of it.


As for this subject - RCDs in bathrooms:

701.415.2(iv), (v) & (vi.) [omission of supplementary bonding] uses the term "all circuits of the location" while 701.411.3.3 [modern RCD application] uses "circuits serving the location".
Not much difference but the former could mean just the parts of circuits in the location and the latter the complete circuits which go to the location. Sort of makes sense, I think.

701.411.3.3 also requires RCDs on circuits passing through zones 1 and/or 2 "not serving" the location.
Is this really necessary? Does it assume one may be drilling while taking a bath?

I have always assumed that's what it meant but have just thought:
If under the floor is not in a zone, then why is buried in the wall considered to be or does it only mean cables in trunking or even clipped?

It also ignores the former limitation (for supplementary bonding) of items being simultaneously accessible exposed- and extraneous-conductive-parts. There may be neither.
 17 April 2017 11:13 PM
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spinlondon

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Ebee.
The definition makes my TV a circuit, but it doesn't matter as BS7671 requires us to connect all final circuits to a separate way in a DB.
So who's now going to argue that an FCU is the same as a DB?
Who's going to be installing AMD 3 compliant FCUs or enclosing plastic FCUs in metal boxes?

Geoffsd.
The original wording "all circuits of the location" has been changed because people didn't understand that it means circuits passing through the location as well as those serving the location.
The new Regulation 701.411.3.3 is not a new requirement, though now it only requires circuits passing through the zones be provided with RCD protection rather than all circuits passing through the location.

In the 16th edition circuits were not allowed to pass through zones 0, 1 & 2, unless they served equipment in a zone or were embedded in walls at a depth greater than 50mm, or had mechanical protection or an earthed sheath or earthed containment.
The 17th edition allowed circuits to pass through zones 1 & 2, as long as they also have RCD protection.
As far as I am aware such circuits still have to be embedded at a depth greater than 50mm, or have mechanical protection or an earthed sheath or earthed containment.

One thing that was pointed out by Mark Coles, is that the requirement was not for each circuit to be provided with RCD protection, but for all circuits to be provided with RCD protection.
Mark argued that if you were to install a new circuit into the location, you would be required to provide RCD protection for all circuits of the location, not just the circuit you installed.
 17 April 2017 11:17 PM
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mapj1

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I often do find myself thinking it would be clearer if the regs said what they meant, and that can involve some naval gazing and asking 'what the !"$$ was really the intention of this one?'
Things like 'serving' are to me a pompous and ambiguous choice of verb.
Some pithy word or phrase, like 'in' or 'from CU upto ' would clarify the intent.
I have the same problem with folk who want to know if I enjoyed my driving experience, instead of asking if I had a good trip.. It may be an age thing.

The other side of this to ask is 'well what is a sensible way to achieve the desired end, and do I care if later someone decides to interpret the regs in a way that makes it non-compliant, if at the big picture level, it meets the intention in terms of safety and is equivalently good?
Could I defend this design as adequate, is it as good as or ideally better than what it replaces ?

-------------------------
regards Mike
 17 April 2017 11:47 PM
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spinlondon

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Much mention has been made of the Emma Shaw case, where a plasterboard screw penetrated a cable causing a line to earth fault and damaged the CPC.
If such were to occur in this case you could have a situation where the CPC down stream from the screw becomes energised.
This would not be picked up by the RCDFCU, the CPC would be live within the location.
Hopefully the supplementary bonding will, wait we no longer have to install supplementary bonding.
Not to worry, the shower is in a plastic enclosure so no exposed conductive parts.
The shower hose is probably not connected to anything conductive and the feed pipe is probably plastic, anyway water doesn't conduct electricity.
 18 April 2017 12:12 AM
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mapj1

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The saving grace is that here in the UK, even on a bad day, things are pretty reasonable most of the time - here is a shower that relies on the water being a reasonable insulator
Not for use in the UK of course, and I am not sure how well it would work with an RCD. However, despite the title 'suicide shower' they are pretty safe and reliable in countries where they are used, if a bit tingly for tall people in districts with heavily chlorinated water...

Events like the Emma Shaw case are mercifully rare - requiring a tragic and very unlikely sequence of events, with multiple failures. I agree, for cable damage accidents like that an RCD as near the origin as possible, perhaps even something in the meter tails would have been the best, and actually I'd not be against something like that being mandated for TNx as well as TT.

The interesting side question it raises is the value of testing - I know it was not done properly in that specific case, but if it had been would it have always found the damage before energisation. Certainly there are a number of ways to damage a cable and expose a live, that do not show up on test.

-------------------------
regards Mike
 18 April 2017 12:49 AM
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spinlondon

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Considering that the CPC was broken, I would have expected a simple test for continuity would have been sufficient.
It could be that an R1+R2 test was conducted during construction before the screw penetrated the cable, howeve a Zs test after energisation would have shown the lack of continuity.

There was talk that an IR test would have shown the fault, but I doubt that as the metal stud was not earthed.
 18 April 2017 01:25 AM
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geoffsd

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Originally posted by: spinlondon

Mark argued that if you were to install a new circuit into the location, you would be required to provide RCD protection for all circuits of the location, not just the circuit you installed.


That's the trouble.

It should not be down to someone arguing about it.

The converse can also be argued and would seem more likely to be the case.
 18 April 2017 03:37 AM
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spinlondon

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Despite having disagreed quite forcibly with Mark, I do now have to concede he has a point.
If we extend a socket circuit, we can either provide RCD protection to the circuit, thus providing the extension with RCD protection and at the same time protect all the existing sockets, or we could just install RCD sockets and ignore the existing sockets as we did not install them.
In any event as long as the sockets we install are RCD protected, we have complied with the requirements.

Similarly with cables concealed in walls.
If we extend a circuit we can run the cables on the surface, we can use a cable which incorporates an earthed sheath, etc.
As long as the work we carry out complies we can ignore the existing.

In horticultural/agricultural installations, the requirement is to provide socket circuits with RCD protection.
If we were to extend an existing socket circuit which didn't have RCD protection, we would have to provide RCD protection for all of the circuit existing and new.
Providing protection for just the extension would not comply.

However with locations containing baths and showers, it's slightly different.
BS7671 does not simply state circuits of the location require RCD protection, it states 'all' circuits of the location require RCD protection. By only providing RCD protection to the circuit we are working on, we have not complied with the requirement.

Edited: 18 April 2017 at 03:47 AM by spinlondon
 18 April 2017 10:30 PM
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AJJewsbury

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Andy.
One, you obviously have more knowledge of religion than I do.

Probably not, although a Welsh non-conformist upbringing, if nothing else, did leave a tendency to do my own reading and my own thinking (whether that results in correct or socially acceptable answers is a different issue of course).

As for interpretation, it seems to me that you are the one doing the interpreting, rather than just taking what is stated at face value.

Given the vagaries of the English language (let alone committeeized englisheese) there's surely an amount of interpretation in most reading. If you want something to digest on face value, why not the BS 7671 definition of a circuit on page 24 of the BYB).

Two, as far as I am aware, the purpose of BS7671 is to protect persons, livestock and property, not just persons.
Then again providing RCD protection to the fixed wiring would help protect persons.

Indeed, but I was referring to the specific requirement for RCDs for bathroom circuits - regulation 701.411.3.3 - which specifies that they're specifically for additional protection. I hadn't considered livestock in bathrooms - maybe that's something you have more knowledge of than me.

Three, where does it state that the scope of BS7671 only refers to fixed wiring?

Ah, you've mis-interpreted - your TV is out of scope from BS 7671 by virtue of being covered by more specific appliance standards as I'm sure you know; it's out of scope of building regulations by being non-fixed wiring. Thus as long as the wiring is non-fixed it's out of scope of both sets of regulations. (it it was fixed it would only be out of scope of one of them, not both.)

Four, seen by who?

The designer (or other reader of BS 7671).

I see you have swerved answering Five.

Not at all - its answer was inferred in point 4.

You're still avoiding my questions - would you be happy that a 1-way CU with a 30mA RCCB incomer just outside the bathroom instead of the suggested RCDFCU would comply with BS 7671?

and how does your reading of BS 7671 on this subject align with BS 7671's definition of a circuit?

- Andy.
 18 April 2017 11:24 PM
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ebee

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Spin,
I doubt BEAMA actually meant what you think they did.
However that might be down to their wording rather than any error on your part (i downloaded the article but unforntunately cant read it on the machine I am using at the moment).

Anyway an RCD gives protection to downstream wiring not upstream and that includes t & e, flex or wet string.

I did think that an RCD say SFCU for instance would give adequate protection in a bathroom etc and therefore fullfill the requirements, however , I think it was OMS pointed out that if such an RCD was at the end of an existing lighting circuit whose disconnection time was long (5 seconds example) and the cpc was at say half mains voltage due to a fault external to the bathroom prior to the RCD then the rcd would not see it. So the benefits of the bathroom RCD might be lost in this example. Accordingly we might think of it as being part of a circuit and not THE CIRCUIT of the bathroom.



Of course the definition of circuit says otherwise but we must evaluate this scenario

One arguement is that a sub board would offer the same problem, however a sub board hopefully has more robust earthing.

I think we need tointerpret the regs carefully in each case, therin lies the problem, one mans interpretation is another mans get out of jail free.

I certainly do not feel as comfortable just adding an RCD FCU for bathroom only as I once might have

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
IET » Wiring and the regulations » 13amp fused RCD

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