another 2391 question

[Deleted member 26818]

As far as I'm aware, the only Regulation which would require 30mA RCD protection for an office circuit, is: 705.411.1.
This would only apply if the office is in/on Agricultural/Horticultural premises, and is supplying socket-outlets.

 

[CrazyScozzese]

Surely, the answer is simply, "where the installation includes sockets that are not intended for use by skilled or supervised persons"

 

[CrazyScozzese]

Not exceeding ....yada...

 

[tex431]

The whole question. (not sure on date)
17. State
a)One condition where BS 7671 requires a 30mA RCD to provide additional protection to a circuit in an office.
b)the maximum permitted disconnection time of the RCD in a) above, when a current of 150mA flows to earth
c) the maximum permitted earth fault loop impedance of a circuit forming part of a TT system, if it is protected by a 300 mA RCD.

The part B section relates to a six year old office building

 

[Deleted member 26818]

Surely, the answer is simply, "where the installation includes sockets that are not intended for use by skilled or supervised persons"

That only applies to the socket-outlets, not the circuits supplying them.
Whilst placing the RCD protection at the origin of a circuit, may be the easiest or cheapest solution, it is not a requirement of BS7671.
As I've already stated, the only reference to providing RCD protection for circuits in BS7671, is where those circuits are of a special location.

 

[spark 68]

Good 'ol C&G, as cryptic as ever

 

[Deleted member 26818]

The whole question. (not sure on date)
17. State
a)One condition where BS 7671 requires a 30mA RCD to provide additional protection to a circuit in an office.
b)the maximum permitted disconnection time of the RCD in a) above, when a current of 150mA flows to earth
c) the maximum permitted earth fault loop impedance of a circuit forming part of a TT system, if it is protected by a 300 mA RCD.

The part B section relates to a six year old office building

The fact that TT is referred to in the third part of the question, suggests that the answer to the first part would involve TT as well.
However, there is no requirement for a TT system to have RCD protection.
An RCD is just the preferred option.
It could just be a red herrring.

 

[CrazyScozzese]

Nope, Spin old chum, too deep. If the circuit supplies sockets yada yada would be an acceptable answer. Why would you think that you were supposed to presume that all the sockets had individual protection? It doesn't say so in the question. The simplest answer is invariably correct.

I am not argueing with your detail or interpretation of the regs, that is spot on. I am saying that the question does not presuppose any extra detail that is not mentioned.

However, also acceptable would be that it includes the cables which form part of the circuit, and they may not be at the correct depth or mech protected, so without supervised use, they too reqiuire 'additional' protection by an RCD.

Two answers for the price of one.

Look guys, if you are sitting these exams, use the old adage, if you find hoof prints, don't look for zebras. The office part precludes NOTHING if the users are unsupervised or unskilled. Same rules apply.

 

[CrazyScozzese]

And sorry, but a TT does have a requirement for an RCD if the disconnection times cannot be met due to the impedance of the earth fault path.

 

[Deleted member 26818]

Sorry, could you please furnish us with the number of the Regulation that requires Circuits that supply socket-outlets to have RCD protection?
I'm not presuming that the socket-outlets have individual protection, just pointing out, that the requirement for RCD protection refers to socket-outlets, not the circuits that supply them.
Again could you please furnish us with the number of the Regulation that requires Circuits with cables concealed in walls to have RCD protection?
As for your last statement, the fact that the question refers to an office, and the OP indicates that the premises is an office building, suggests that the installation is not domestic, but is a work place.
As such the EAWR would apply.
Regulation 16 of the EAWR requires that anyone carrying out a work duty, meets the requirements of BS7671 to be considered a skilled or instructed person.
Therefore the exemptions to the requirement to provide RCD protection for socket-outlets, and cables concealed in walls would be applicable.

Finally, could you also furnish the number of the Regulation, that requires TT installations to have RCD protection?

 

[CrazyScozzese]

Spin, in reverse order- TT.

Did I say there was a REG number that said there was, no. Don't wiggle out of being corrected by playing with my words. Read exactly what I said. That said, I think 411.5.2 note 1. covers it. Even so, I am fairly certain that the 'essence' (look that up in legal definitions) of the IEE/IET/EAWR publications cleary say that a TT should have an RCD, and especially where the disconnection times cannot be met by normal means. YES they also allow for deviation, and exception, which is what you are getting at, but I can see you standing in the dock argueing why you went against everything and did not fit an RCD where the disconnection times could not be met. That would work.

I need a beer. Back in 5.

Why advise people of loop holes? Is it not better to go down the better safe than sorry route?

 

[CrazyScozzese]

Second Spin. Look at the question posted. State: One condition where BS 7671 requires a 30mA RCD to provide additional protection to a circuit in an office.

OK, state. means very short answer. No mention of EAWR. No mention of Skilled. Some office have public access, young people, etc. How do you know they have been supervised or trained as per s16? Did you get it in writing? DOES it say that in the question no.

Simple answers to simple questions. There are a lot of regs that agree with what I said, and I can't be bothered looking them up, I remember the 'essence' of what they say, not the numbers. Life is too short and I have killed too many cells.

The question didn't ask under which circumstances you would be able to avoid fitting an RCD where you would normally fit one to comply, but are looking for a loop hole not to.

 

[Deleted member 26818]

Spin, in reverse order- TT.

Did I say there was a REG number that said there was, no. Don't wiggle out of being corrected by playing with my words. Read exactly what I said. That said, I think 411.5.2 note 1. covers it. Even so, I am fairly certain that the 'essence' (look that up in legal definitions) of the IEE/IET/EAWR publications cleary say that a TT should have an RCD, and especially where the disconnection times cannot be met by normal means. YES they also allow for deviation, and exception, which is what you are getting at, but I can see you standing in the dock argueing why you went against everything and did not fit an RCD where the disconnection times could not be met. That would work.

I need a beer. Back in 5.

Why advise people of loop holes? Is it not better to go down the better safe than sorry route?

I'm sorry, but your posts in this thread have been rather pointless.
This thread is in relation to a question from the 2391 exam.
An exam that as I understand it, requires the examinee, to show a thorough understanding of BS7671 and the requirements therein.
I am also reliably informed, that the examiners for the 2391 are very hot on use of correct terminology and units of measurement.
It's not about loop holes, or wiggleing when being corrected (particuarly as I haven't been corrected in this thread).
It's about reading the question, determining what is being asked, and answering the actual question, not what you think is the question.

I will once again, point out that the question refers to a circuit, and that in BS7671, the only place where there are requirements for RCD protection for a circuit, is in Chapter 7 (Special Locations).
In the general part of the BS7671 Chapters 1 to 6, there are requirements for additional protection for socket-outlets, mobile equipment used outdoors, and for cables concealed in walls, that are not provided with another acceptable method of additional protection.
There is no requirement in BS7671 for RCD protection in a TT installation, it is the preferred method.
When an RCD is used as fault protection in a TT system, the RCD is not then considered as additional protection.
The question from the 2391 exam paper, asks for one condition, where additional protection is required.
Therefore it is not neccessarily a TT system.
The question indicates that the installation is an office, as such the requirements that apply to ordinary persons are not applicable.
The question refers to a circuit, so the requirements of BS7671 that apply to anything that is not a circuit are, not applicable.

 

[Deleted member 26818]

Second Spin. Look at the question posted. State: One condition where BS 7671 requires a 30mA RCD to provide additional protection to a circuit in an office.

OK, state. means very short answer. No mention of EAWR. No mention of Skilled. Some office have public access, young people, etc. How do you know they have been supervised or trained as per s16? Did you get it in writing? DOES it say that in the question no.

Simple answers to simple questions. There are a lot of regs that agree with what I said, and I can't be bothered looking them up, I remember the 'essence' of what they say, not the numbers. Life is too short and I have killed too many cells.

The question didn't ask under which circumstances you would be able to avoid fitting an RCD where you would normally fit one to comply, but are looking for a loop hole not to.

Again you are making something out of nothing.
The question relates to a circuit. Whether a person is skilled, instructed or ordinary, is immaterial.
Where BS7671 requires RCD protection for circuits there are no exemptions for skilled or instructed persons, the requirements apply for everyone.
It doesn't matter whether i know if they have been supervised trained or anything else, I don't need it in writing.
The EAWR is a statutory requirement, if the person is not experienced enough, not qualified or supervised, then whatever they are doing is illegal.
BS7671 does not bother with situations where people act illegally, as those people are hardly going to take note of some non-statutory Regulations, if they can't be asked to comply with statutory requirements.
It will not help you to pass the exam, if your simple answer is to a question that has not been asked.
If there are lots of Regulations that agree with what you have posted, then furnish us with the numbers. Put up or shut up.
I'll refrain from commenting on the admitted lack of brain cells.
I agree, the question didn't ask under what circumstances blah, blah, blah.
The question askes for one condition wher RCD protection would be required.
The fact that it asks for a condition where RCD protection is required, should to my mind be an indication, that such RCD protection is not normally required, that it is a special requirement.
Special as in special location perhaps?

 

[CrazyScozzese]

Calm down old bean.

Your knowledge of the regs is so literal that you concentrate on the exceptions rather than the rule. Most of that above you brought up not me. Let me put it in your language.

Circuit. An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s)

Does that not include the cables and accessories includeing sockets?

I didn't say it was TT, you said it was implied it was! And then said "could you also furnish the number of the Regulation, that requires TT installations to have RCD protection?"

411.5 TT system
411.5.2 One or more of the following types of protective device shall be used, the former being preferred:
(i) An RCD
(ii) An overcurrent protective device.
NOTE 1: An appropriate overcurrent protective device may be used for fault protection provided a suitably low value of Zs is permanently and reliably assured.

So, I said "sorry, but a TT does have a requirement for an RCD if the disconnection times cannot be met due to the impedance of the earth fault path.".

Do you think that the conditional statement PROVIDED has been complied with if the Zs has not be reached, therefor MAY is no longer valid, and the PREFERENCE for RCD part becomes less of an option seeing as the other option is no longer satisfied by the former conditional statement?

As for the pompous stuff about EAWR, Yes your honour, I did not fit an RCD which led to a death because even though I did not ask if the sockets were in use by unskilled persons, it is my belief that the office manager should have ensured the temps and work experience kids knew that they should not plug in their devices and accidentally touch the live pin. Or a fault in the earth on the PC made the case live and she was killed trying to work out why the PC locked up.

Two wrongs do not make a right mate. Just because your superior knowledge knows a way not to do something that is considered to be best practice, that does not make it acceptable to tell novices in a manner that makes it seem standard practice, and so confusing them. The 2391 test rig I worked on had a sign on it that says the sockets on circuit X are for use by skilled persons. The office circuit however did not, and had an RCD covering the sockets.

And yes, if the office had a shower in it, it would be special too.

Look at P150 of the green onsite guide. Looks to me like having a socket without RCD protection in an office used by skilled people IS IN WRITING.

Help me out, as you are trying to argue the ciruit part, if it doesn't include cables, sockets, and mobile equipment, what on earth does it include?

Still love you man, don't get me wrong, healthy debate, still got some man love for that big brain of yours. ;-)