Summerhouse/Outbuilding wiring thoughts?

[333rocky333]

'Additional protection' surely only requires a device which will operate in response to a residual current ≥30mA. If an SRCD cannot be relied upon to do that, then what (if anything) can it be relied upon to do?

Kind Regards, John

I seem to recall when Reg 411.3.3 came in force, fitting an Rcd socket was one suggested method of complying

 

[JohnW2]

I seem to recall when Reg 411.3.3 came in force, fitting an Rcd socket was one suggested method of complying

That would make sense, and it's something that I've often seen suggested here and elsewhere (and long after that regulatory requirement appeared) - but not if the Standard says that RCD sockets (and FCUs) are not suitable for that purpose (and BS7671 doesn't say that they are).

I'm still mystified. What is the point or sense in a residual current device which can only be 'relied upon' if there is another residual current device upstream of it?!

Kind Regards, John

 

[SUNRAY]

For BS7288, it's implied that:
Fault protection - fuse or circuit breaker
Additional protection - from a 30mA RCD to 61008 or 61009 (as in section 415 in BS7671)
Supplementary protection - the undefined purpose that a socket outlet RCD provides.

Dictionary definitions of words and what they mean in certain standards are generally unrelated.
The meaning of words in one standard are often completely different to the same words in another standard.
One standard directly conflicting with another is a regular event.
Colossal mistakes and obvious blunders are commonplace.

Given the mess that was added in BS7288:2016 which made the whole point of the devices entirely irrelevant, those who amend BS7671 had no other choice but to remove any reference to it.

BS means British Shambles.
BS EN is the British Shambles version of European Nonsense.
It's not supposed to make sense.


View attachment 239990

So what does SRCD actually stand for?

 

[bernardgreen]

SRCD. (Socket-Outlet incorporating a Residual Current Device). according to several websites

 

[BS3036]

I'm still mystified.

I spent some time yesterday scouring the internet. It seems to be a minefield of misinformation and people quoting other people but very little source information. The closest I have come to some factual data relates to the paragraph in BS 7288: 1990 (amended 1993):

7.13.2 The isolation distance between contacts in
the same conductive path shall be at least 3 mm.
Compliance shall be checked by inspection and
measurement.

It has been suggested that this requirement was removed in the 2016 version, with the justification that isolation could be achieved by pulling out the plug. The suggestion seems to be that the 3mm isolation path was interpreted by the authors of BS 7671 to be required to occur as part of the automatic disconnection process, and therefore prevented the device from being considered as a useful RCD.
I do not have access to the 2016 version, so can't confirm this.

I do find it alarming that there should continue to be so much confusion around this, which has been going on for years now. It seems to confirm the opinion of some, that BS 7671 is authored by a committee comprising mostly people with a vested interest in inventing the requirement for more and more expensive kit, rather than writing clear and sensible rules for keeping people safe.

 

[SUNRAY]

SRCD. (Socket-Outlet incorporating a Residual Current Device). according to several websites

Which is EXACTLY my expectation, also confirmed in JW's posted document:

however from the same document:

My first interpretation when read from the full text:

was

and assumed a typo as the operation performed by any RCD device is so clearcut I wouldn't have imagined it needed to be stated in a document of this type.

My interpretation of this:

may be different to others, in the case of the heaters circuit I posted before, A radial circuit in steel conduit with no socket outlets did not require additional protection (whatever that definition may be) The OCD was adequate for the circuit and the steel tube gave additional protection to the wires. On that basis adding a RCD to the end of the circuit gave the additional protection to the socket.

Other than the effectiveness/reliability/design of SRCDs, I personally don't see an issue with such a circuit.

 

[EFLImpudence]

'Additional protection' surely only requires a device which will operate in response to a residual current ≥30mA.

Yes.

411.3.3 states that "additional protection by means of an RCD in accordance with regulation 415.1 shall be provided for" amongst other things socket outlets.

415.1 states a maximum 30mA and the required trip time.

Particular RCD devices are not mentioned therefore not required.

People are talking as if "additional protection" is a particular thing in itself - as they do for "supplementary bonding" - rather than just meaning 'extra'.

 

[EFLImpudence]

Saying a a BS61008/9 RCD can only be used as additional protection does not mean only a BS61008/9 RCD can be used as additional protection.

 

[flameport]

It has been suggested that this requirement was removed in the 2016 version

It was removed. The changes to the 2016 version were extensive, most of the content was deleted entirely and replaced with new. The numbering in the document also changed significantly, and the new is substantially larger than the old - the 1990 version is 32 pages, the 2016 one has 126 pages. It's an entirely different document.

In the new version, isolation is only mentioned in that removing the plug is isolation, and it's not necessary for the SRCD itself to provide any isolation function.

 

[flameport]

For an idea of what's in the 2016 version, there is a preview here: https://shop.bsigroup.com/ProductDetail/?pid=000000000030337151 which has the contents, introduction and scope. ('click to preview' button to the right of the buying options)

Another better quality preview here: https://webstore.iec.ch/publication/22390 which is the document that BS7288:2016 was created from. There are some changes and items not included, but it's substantially the same.

 

[JohnW2]

I spent some time yesterday scouring the internet. It seems to be a minefield of misinformation and people quoting other people but very little source information.

Quite so - as you go on to say, confused/confusing and, as I said, mystifying to me.

I do find it alarming that there should continue to be so much confusion around this, which has been going on for years now. It seems to confirm the opinion of some, that BS 7671 is authored by a committee comprising mostly people with a vested interest in inventing the requirement for more and more expensive kit, rather than writing clear and sensible rules for keeping people safe.

I'm less inclined than many to believe that a committee as large as JPEL/64 can be dominated by people being influenced by such vested interests, so am initially more inclined to say something on the lines of "they don't know/understand what they are talking about". However, many/most of them do have training/qualifications that means that they should "know/understand", so it is perhaps a case of their not thinking about things carefully enough - i.e. not being adequately conscientious in relation to their committee work. My late father was, over the years, on some BSi committees and I have to say that I don't recall him talking such activities all that 'seriously'.

I remain conceptually mystified. I just find it difficult to see why these devices, let alone a Standard relating to them, exist, if, although 'residual current devices' are deemed not to be reliably enough to operate in the presence of a residual current of In, to the extent that they should only be used if the same functionality is provided by a separate upstream device. I suppose what you say about the 3mm contact separation might 'explain' how this situation/confusion has arisen, but it still doesn't help me to understand why anyone would bother to use such a device if they were required to have another 'proper' RCD upstream - unless, I suppose if they wanted the 'NVR' functionality of an active RCD (but then they could be 'NVR sockets, rather than RCD ones).

Kind Regards, John

 

[SUNRAY]

I haven't, and don't intend to, read the whole of BS7288.

BUT I don't see a sentence that specifies:
"A SRCD must be preceeded by a RCD" (in whatever wording may be applicable) in the few clips I have seen. I've seen 'additional' and 'supplementary' but these don't have to be RCD... OR has that now become the new rule?

One of the things I have been aware of is a whole new build estate with a 16A MCB, SWA radial directly from CU to garage, SRCD, SFRCD with 3A fuse for the light.
I suspect it would have been cheaper to install RCBO, DSSO & FCU but I do see why that's not a good plan.

 

[flameport]

As described in BS7671, 'additional protection' is either 'the use of RCDs with a rated residual operating current not exceeding 30 mA' or 'supplementary protective equipotential bonding'.
Section 415.
One of which limits the duration of a shock, the other limits the voltage.

There are situations where neither are required (such as the heater circuit in steel conduit), but those are the exceptions and certainly not the majority of installations, particularly for socket outlets in domestic and smaller commercial environments.

 

[BS3036]

Interestingly, IEC 62640:2011 (from which BS 7288: 2016 was developed) has the sales pitch:
IEC 62640:2011+A1:2015 applies to residual current-operated devices (RCD) incorporated in, or specifically intended for use with two pole socket-outlets, with or without earthing contact for household and similar uses (SRCD: socket-outlet residual current devices). SRCDs, according to this standard, are intended to be used in single phase systems such as phase to neutral or phase to phase or phase to earthed middle conductor. SRCDs are only intended to provide additional protection downstream of the SRCD. SRCDs are intended for use in circuits where the fault protection (indirect contact protection) is already assured upstream of the SRCD.
(My emboldening).
It looks like the pitch to BS 7288: 2016 had the bit about additional protection added. Possibly by an over-zealous editor.

 

[EFLImpudence]

That makes sense - and is rather obvious.

There is nothing to say that the indirect contact protection has to be another RCD therefore the socket will be the additional protection.