another 2391 question

[Deleted member 26818]

Can't be asked.

 

[CrazyScozzese]

I was suffering from insomnia last night.

 

[Englishman]

Nice helpful comment there Ian, so thanks for that eh.

I take it the OP is doing the written on 9th Feb? It's the date i'm taking 2391 for the first time think they're all done at the same time? From going through past papers, there seems to be a lot of odd questions where specific provision doesn't seem to be in either GN3 or BS7671:2011, let along BS7671:2008, bit of a ****take imo to include the laest 7671 update in the test just months after it's been released but it's not something that surprises me.

 

[JUD]

Sorry, could you please furnish us with the number of the Regulation that requires Circuits that supply socket-outlets to have RCD protection?

Try Regs 522.6.101, 522.6.102 & 522.6.103 in the BGB.

Cables installed at ≤ 50mm in a wall or partition require additional protection by an RCD unless they are mechanically protected using one of the methods in 522.6.101.

Cables installed in a wall or partition which includes metallic parts (excl. nails, screws etc.) require protection by one of the methods in 522.6.103 (which includes additional protection by means of an RCD as an option).

They apply to all circuits not under the supervision of a skilled or instructed person.

The question in the OP asks for one condition where BS7671 requires additional protection by an RCD, NOT for exceptions.

 

[Deleted member 26818]

JUD the those Regulations do not refer to or even mention circuits. They refer to cables.
Also in those Regulations, RCD protection is not a Requirement, just an option.
As I have said now on a number of occasions, the only place where you will find requirements for RCD protection for circuits, is in Chapter 7.

The question in the OP asks for one condition where BS7671 requires additional protection by an RCD, NOT for exceptions.

Exactly, a condition where the additional protection is required, and no exceptions are allowed.
If the question asked for one condition where 30mA RCD protection is required for socket-outlets in an office, the answers would be where the socket-outlets are intended to be used by ordinary persons, or are used to supply mobile equipment outdoors.
If the question asked for one condition where 30mA RCD protection is required for cables concealed in walls of an office, the answer would be where the cable is at a depth less than 50mm, does not have an earthed metallic sheath, is not in earthed conduit or trunking, does not have mechanical protection sufficient to prevent penetration by screws or nails and the office is not under the supervision of a skilled or instructed person.
i.e. a home office, or an office in a domestic installation.
If the question asked for one condition where a circuit requires 30mA RCD protection, one answer would be when the circuit is of a location containing a bath or shower.
As it's unlikely that an office will have a bathroom or shower-room, and even if the office did, as the building is six years old, the bath or shower room, would not have socket-outlets, as the Regulation allowing socket-outlets in such locations, did not exist six years ago.
The question asks for one condition where irrespective of the installation method for the cables, irrespective of the use the sockets are intended for, irrespective of whether there is supervison by a skilled or instructed person, a condition where in every instance, the circuit will require 30mA RCD protection.
There is only one condition that would in every instance require an office circuit that supplies socket-outlets to be provided with 30mA RCD protection, and that is when the office is part of an Agricultural/Horticultural installation.

 

[CrazyScozzese]

JUD the those Regulations do not refer to or even mention circuits. They refer to cables.
Also in those Regulations, RCD protection is not a Requirement, just an option.
As I have said now on a number of occasions, the only place where you will find requirements for RCD protection for circuits, is in Chapter 7.


Exactly, a condition where the additional protection is required, and no exceptions are allowed.
If the question asked for one condition where 30mA RCD protection is required for socket-outlets in an office, the answers would be where the socket-outlets are intended to be used by ordinary persons, or are used to supply mobile equipment outdoors.
If the question asked for one condition where 30mA RCD protection is required for cables concealed in walls of an office, the answer would be where the cable is at a depth less than 50mm, does not have an earthed metallic sheath, is not in earthed conduit or trunking, does not have mechanical protection sufficient to prevent penetration by screws or nails and the office is not under the supervision of a skilled or instructed person.
i.e. a home office, or an office in a domestic installation.
If the question asked for one condition where a circuit requires 30mA RCD protection, one answer would be when the circuit is of a location containing a bath or shower.
As it's unlikely that an office will have a bathroom or shower-room, and even if the office did, as the building is six years old, the bath or shower room, would not have socket-outlets, as the Regulation allowing socket-outlets in such locations, did not exist six years ago.
The question asks for one condition where irrespective of the installation method for the cables, irrespective of the use the sockets are intended for, irrespective of whether there is supervison by a skilled or instructed person, a condition where in every instance, the circuit will require 30mA RCD protection.
There is only one condition that would in every instance require an office circuit that supplies socket-outlets to be provided with 30mA RCD protection, and that is when the office is part of an Agricultural/Horticultural installation.

Spin, If I apply the logic you used on my and other answers to your comment, you are still wrong.

If we are to believe that they are excluding sockets and cables when they say circuit, and are looking for a situation where their recommendations, preferences and general good practices are ignored, then S705 would only require a 300ma RCD for all other circuits. As they did not say to protect sockets, that part would not apply, under your rules.

It is not that complex, if you find hoof prints in your garden, don't search for zebras.

There are a lot of answers, they are trying to get you to think of the scenario.

7.2.5 Requirement for RCDs
RCDs are required:
i where the earth fault loop impedance is too high to provide the required disconnection, for example, where the distributor does not provide a connection to the means of earthing – TT earthing arrangement
ii for socket-outlets where used by ordinary persons for general use
iii for all circuits of locations containing a bath or shower
iv for circuits supplying mobile equipment not exceeding 32 A for use outdoors
v for cables without earthed metallic covering installed in walls or partitions at a depth of less than 50 mm and not protected by earthed steel conduit or similar
vi for cables without earthed metallic covering installed in walls or partitions with metal parts (not including screws or nails) and not protected by earthed steel conduit or the like.

RCD protection can be omitted in the following circumstances:
i specific labelled socket-outlets, for example, a socket-outlet for a freezer. However, the circuit cables must not require RCD protection as per v and vi above, that is, circuit cables must be enclosed in earthed steel conduit or have an earthed metal sheath or be at a depth of at least 50 mm in a wall or partition without metal parts
ii socket-outlet circuits in situations where the use of equipment and work on the building fabric and electrical installation is controlled by skilled or instructed persons, for example, in some industrial and commercial locations; see 3.6.2.2.

Cables installed on the surface do not specifically require RCD protection, however, RCD protection may be required for other reasons, such as where the installation forms part of a TT system and the earth fault loop impedance values for the overcurrent protective device cannot be met.


And to clarify the point about getting it in writing if you choose to omit an RCD:-


3.6.2.2 Installations under the control of skilled or instructed persons
BS 7671:2008(2011) permits RCDs, where usually provided for additional protection, to be omitted where the installation is under the control of a skilled or instructed person.
The decision as to which socket-outlets or circuits do not require additional protection by RCDs should be taken by the designer of the electrical installation and only after consultation with an appropriate person in the client’s organisation. An appropriate person would be one who is able to ensure that the socket-outlets or circuits in question are, and will remain, under the supervision of skilled or instructed persons.
Wherever a designer so chooses to omit RCD protection, traceable confirmation must be obtained from the client to identify the reason for the omission and such confirmation must be included within the documentation handed over to the client upon completion of the work.
Where no such confirmation can be obtained, RCD protection should not be omitted.

 

[Deleted member 26818]

A very well thought out and thourough argument, except that the question relates to circuits, not to items of equipement that are just a part of a circuit.

Iagree, that the question does not specify what it supplies, however it does specify that 30mA RCD protection is required.
Circuits that supply socket-outlets in Agricultural/Horticultural installations in all instances require 30mA RCD protection. No exceptions.

 

[CrazyScozzese]

A very well thought out and thourough argument, except that the question relates to circuits, not to items of equipement that are just a part of a circuit.

Iagree, that the question does not specify what it supplies, however it does specify that 30mA RCD protection is required.
Circuits that supply socket-outlets in Agricultural/Horticultural installations in all instances require 30mA RCD protection. No exceptions.

Typical IET questions, cryptic, designed to confuse and trip you up. With several possible answers depending upon how you interpret it, just like the regs themselves. Enjoyed the debate though.

 

[brman]

Typical IET questions, cryptic, designed to confuse and trip you up. With several possible answers depending upon how you interpret it, just like the regs themselves. Enjoyed the debate though.

As someone watching this discussion with interest (I'll be doing my 2395 in April) I completely agree. If you guys can argue over the answer for this long what hope is there for us mere mortals

 

[tex431]

Is there not anyone on here from C&G's who would clarify the appropiatly worded answer C&G want?

 

[CrazyScozzese]

If you get the question in the exam, just write down a link to this thread...

 

[41steve]

Think i need to do the 17th. No RCD protection on a TT system?

Is that what spinlondon is saying or have i missed the question?

 

[Deleted member 26818]

Think i need to do the 17th. No RCD protection on a TT system?

Is that what spinlondon is saying or have i missed the question?

It's the preferred option.

 

[kenny james]

FFS does every simple question on this forum always have to go into a war of words between sparks and the answer never gets answered without disputes!

 

[CrazyScozzese]

Cos the regs are a beautiful work of mutli coloured art.

And beauty is in the eye if the beholder.

The regs say, it should be this size, unless you prefer to use this formula, except if it has been ok or if xyz applies, then do this or you decide.

What is the problem, they are empowering you to stand up and shoulder the resposibility.

Lead by example.