Max Zs

[Apache]

have a pint then instead Guiness Drink

Guiness Drink aye

 

[SPECIAL LOCATION]

Sorry, i well have to ensure my posts are full, accurate and explain all possible commutations of the answerok here goes

under the 17th edition, where MANY circuits are RCD protected, and the RCD satisfies the requirement for ADS in the event of a fault to earth, then the Zs value relating to any particular CPD used in conjunction with the RCD becomes irrelevent, as the RCD will operate before the fault touch voltage exceeds 50V providing that the EFLI of the RCD protected circuit is 1667 ohms or less. As such, concerning yourself with whether or not a 32A Type B BS EN 60898 MCB is below a tabulated value of 1.44 ohms is a futile exercise where the circuit is protected by a 30mA residual current device.

i am not implying that ZS is irrelevent OR putting RCD's on every circuit.

now while you try and pick holes in that statement, i am off to bed:z

Am I allowed to type a reply to this post without being accused of picking holes...

being argumentative/aggressive etc.. etc..Pray:x

side note ;

obviously one persons opinion of healthy debate .... after deliberately trying to provoke debate... but then not liking the way others may type there answers because it brings into question their understanding is not necessarily the same as others?

Also not helped by other members comments re-picking fights? phtt!

Indeed, I am at a loss as to how to debate without referring to the posts others make e.g. quoting, without then being shot at for identifying apparent errors in a statement.. which too me is what the debate and discussion is all about..

And which by its very nature would involve a level of personal opinion which can either be backed up with other reference material.. to verify a point of view or not! in which case it is just personal unverified opinion!.

I am all for people having their own opinions.... But personally I do heed more attention to those that are able to back by any specifics with references!

If anyone is offended by that again I am sorry

And as Paul M said

but isn't that the pure essence of what a forum is surely if we all just agreed on everything it would just become a self appreciation society,as we all know the regs are not always clear cut and this leaves certain things open to interpretation,so a good natured open discussion does help to clear up some of the more vague regs,does it not is not written how they like it

If you are just expecting wholehearted agreement both in content and style of posting, without constructive discussion then that ain't a forum IMHO:|

again I would point out I don't do name calling or abusive language which are totally unnecessary & admin would step in anyway if that occurred!

so Mr Shakey SirGuiness Drink

re:-

under the 17th edition, where MANY circuits are RCD protected, and the RCD satisfies the requirement for ADS in the event of a fault to earth, then the Zs value relating to any particular CPD used in conjunction with the RCD becomes irrelevent, as the RCD will operate before the fault touch voltage exceeds 50V providing that the EFLI of the RCD protected circuit is 1667 ohms or less. As such, concerning yourself with whether or not a 32A Type B BS EN 60898 MCB is below a tabulated value of 1.44 ohms is a futile exercise where the circuit is protected by a 30mA residual current device.

I would agree entirely that in a real world situation an RCD would, (as long as it is not jammed), operate faster than an MCB in the event of an earth fault. {tho I have seen failed RCDs & assume most others have to?}

BUT.... (assume we are talkin TN installations NOT TT for the moment)

an RCD is classed as "ADDITIONAL PROTECTION" and is NOT recognised as the sole means of protection. I believe regs 415.1, 415.1.1, 415.1.2 clarify this bit. The ADS "Automatic Disconnection of Supply" should still have a device complying with section 411. whereby the Zs values are still relevant.

otherwise... they would have been taken out the big red book!

I assume you can agree with this?

or if not point me to the reg I have missed please sir?Blushing:x

cuz I certainly dont know em all! :^O :^O:^O

nor would I claim too... but I now know how to cut rabbits claws!Blushing

Guiness Drink

 

[DonkeyDong]

Where's the popcorn - this is an interesting show

Anyway...not meaning to get involved....But I agree with SP here..under "normal" situations involving TN systems, an RCD is normally additional protection, and the use of MCB/Fuse is still required as the primary means of disconnection (not for all situations/circumstances)

D.

 

[PAUL M]

[quote=SPECIAL LOCATION;23193.. but I now know how to cut rabbits claws!Blushing

What a star apache been giving you private lessons has heGuiness Drink

 

[Shakey]

Am I allowed to type a reply to this post without being accused of picking holes... being argumentative/aggressive etc.. etc..Pray:x

side note ;

obviously one persons opinion of healthy debate .... after deliberately trying to provoke debate... but then not liking the way others may type there answers because it brings into question their understanding is not necessarily the same as others?

Also not helped by other members comments re-picking fights? phtt!

Indeed, I am at a loss as to how to debate without referring to the posts others make e.g. quoting, without then being shot at for identifying apparent errors in a statement.. which too me is what the debate and discussion is all about..

And which by its very nature would involve a level of personal opinion which can either be backed up with other reference material.. to verify a point of view or not! in which case it is just personal unverified opinion!.

I am all for people having their own opinions.... But personally I do heed more attention to those that are able to back by any specifics with references!

If anyone is offended by that again I am sorry

And as Paul M said

If you are just expecting wholehearted agreement both in content and style of posting, without constructive discussion then that ain't a forum IMHO:|

again I would point out I don't do name calling or abusive language which are totally unnecessary & admin would step in anyway if that occurred!

so Mr Shakey SirGuiness Drink

re:-

I would agree entirely that in a real world situation an RCD would, (as long as it is not jammed), operate faster than an MCB in the event of an earth fault. {tho I have seen failed RCDs & assume most others have to?}

BUT.... (assume we are talkin TN installations NOT TT for the moment)

an RCD is classed as "ADDITIONAL PROTECTION" and is NOT recognised as the sole means of protection. I believe regs 415.1, 415.1.1, 415.1.2 clarify this bit. The ADS "Automatic Disconnection of Supply" should still have a device complying with section 411. whereby the Zs values are still relevant.

otherwise... they would have been taken out the big red book!

I assume you can agree with this?

or if not point me to the reg I have missed please sir?Blushing:x

cuz I certainly dont know em all! :^O :^O:^O

nor would I claim too... but I now know how to cut rabbits claws!Blushing

Guiness Drink

well it seems we do agree on something! the right to reply in ones own style, genre, etc. Which considering the response to my original post on this subject (cue extended lectures on the way i should be posting and the content of what i should be posting) is sometthing i should be allowed to do

And yes i delberately provoke debate (but not argument), because those that know - discuss, and those that dont - learn, which was why i post as i do, and why i occasionally give (and shall continue to give) vague answers.

Ok, i have had this discussion many, many times, and there is a common misconception when it is discussed.......

Firstly that i am in someway suggesting that RCD's can be used as the sole means of protection (i am not)

and secondly, "what happens if the RCD fails, as they so often do?". Well what happens when a 60898 fails? come to think of it, when do we ever test either the thermal or electro-magnetic elements of an MCB? The point being that when deisgning a circuit we must surely start with the premise that any protective device selected (including an RCD) will preform its required function - we do not (or should not) design our circuit with the notion that devices are going to fail.

Ok, down to your points raised.

BUT.... (assume we are talkin TN installations NOT TT for the moment)

an RCD is classed as "ADDITIONAL PROTECTION" and is NOT recognised as the sole means of protection. I believe regs 415.1, 415.1.1, 415.1.2 clarify this bit. The ADS "Automatic Disconnection of Supply" should still have a device complying with section 411. whereby the Zs values are still relevant.

yes an RCD CAN be classed as giving additional protection.......against contact with live parts....but must not be relied upon for for primary protection. of course that concerns basic protection , but the discussion is to with max Zs values, which is about fault protection, and is an entriely seperate discussion.

(and i aplogise in advance for any notions of egg sucking, but obviously people will read this who may be learning at the same time.)

I absolutely agree that to satisfy ADS then there should be a device complying with section 411.

But lets also remember one important thing - we are discussing max Zs - ie max earth fault loop impedence

we protect final circuits against overloads, short circuits and earth faults.

the only one of these that is affected by Zs is earth faults. Overloads and short circuits may be protected by fuse or circuit breaker (ie the thermal element and electro-magnetic elements respectively of an MCB),

however, (and yes i will get to the pointBlushing) earth fault protection may be provided by a fuse, circuit breaker OR an RCD

so, an RCD MAY be used as the sole means of protection (as in protective device) against earth faults. Of course you would still have a fuse or MCB for overload/short circuit, but the RCD (alone) can be there for the earth faults.

Now where this is the case, and i would suggest that where a 30mA RCD is used in conjunction with a MCB/fuse then this would nearly ALWAYS be the case, then, to quote a number of notable publications (well quote as best i can without the books in front of meBlushing)

"measuring values of Zs is a futile excersize"

"the value of earth fault loop impedence need only be measured with a low resolution ohmeter capable of measuring values of 1667 ohms"

"For TN systems when protection is afforded by an RCD, the rated residual operating current in amperes times the earth fault loop impedence in ohms should not exceed 50V"

and of course, that is satisfied for a 30mA RCD if the EFLI is 1667 ohms or less.

so, to clarify, an RCD may be used as the sole protective device for protection against earth faults - but not the sole protective device per se, and where it is used as the protecive device against earth faults, the Zs value for that circuit need only be 1667 ohms or less, REGARDLESS of the max value for any MCB / fuse which may be used for overload/short circuit but not selected as the protective device for earth faults.

and before it is raised, I am not in any way suggesting that it excuses the designer from trying to keep the value of Zs as low as possible, or that throwing an RCD at a circuit can be used to cover up poor design/installation

erm....or something? :|

good discussion though? it always is!!!!!

 

[Robbo]

Blimey lads! I only wanted to win a free sausage and egg roll.

And Shakey, you need your NVQ3 to be a proper electrician. Everyone knows that.

 

[PAUL M]

Blimey lads! I only wanted to win a free sausage and egg roll.And Shakey, you need your NVQ3 to be a proper electrician. Everyone knows that.

according to the J.I.B :S

 

[Shakey]

Blimey lads! I only wanted to win a free sausage and egg roll.And Shakey, you need your NVQ3 to be a proper electrician. Everyone knows that.

ha ha Rob, maybe i will go and study then, maybe i will learn what this 'Zs' thing actually is:^O:^O:^O

next stop......JIB cardPray

 

[Robbo]

 

[stringy]

Blimey lads! I only wanted to win a free sausage and egg roll.And Shakey, you need your NVQ3 to be a proper electrician. Everyone

knows that.

dont forget you owe me a bite of that butty!

 

[sirsparkabit]

Thanks guys this is a thread that i think i may of enjoyed apart from all the toing and frowing deciding what was argumentative and who was ect ect.

I would of preffered to have studied the question in hand

without the conflict.

Can we get back to normal niceness from now please

TIA ssab. :x :x:x:x ; ) :^O :^O

 

[Apache]

Lovely detailed reply. Well done Applaud Smiley

But you can't gloss over

well it seems we do agree on something! the right to reply in ones own style, genre, etc. Which considering the response to my original post on this subject (cue extended lectures on the way i should be posting and the content of what i should be posting) is sometthing i should be allowed to do

*shakes head in disappointment*

And yes i delberately provoke debate (but not argument), because those that know - discuss, and those that dont - learn, which was why i post as i do, and why i occasionally give (and shall continue to give) vague answers.

Vague answers DO NOT HELP ANYBODY. I feel it is an awful shame you feel so arrogant not to realise this :|

 

[sirsparkabit]

Apache i hate Gloss:_| :_|

Do not mind a bit of Eggshell though

Mind you i am not walking on them:^O:^O

Wheres our furry friend??

 

[PAUL M]

Vague answers DO NOT HELP ANYBODY. I feel it is an awful shame you feel so arrogant not to realise this :|

i think when you have known the guy long enough to form a truly unbiased opinion you will realise that shakey is not ARROGANT however he does border on being BRILLIANT,but i suppose its difficult for you to comment or understand some of the technicalities of the debate as you are not a spark yourself are you.Guiness DrinkGuiness Drink

 

[Apache]

i think when you have known the guy long enough to form a truly unbiased opinion you will realise that shakey is not ARROGANT however he does border on being BRILLIANT,but i suppose its difficult for you to comment or understand some of the more technicalities of the debate as you are not a spark yourself are you.Guiness DrinkGuiness Drink

I'm open to this brilliance! In fact I'd love to see it. All I've seen so far is arrogance. The only arrogance I've ever come across on here in fact.

It's not what this forum is about

If we have people massaging their own ego's the forum looses its 'difference' and becomes another SF with the associated ***** measuring :|

 

[spark-doctor]

Vague answers DO NOT HELP ANYBODY

On the contrary, to use ones brain to disassemble the information or to build on the information given is the best form of education there is.

When you were training to be a bovine proctologist, did your tutors just give you the answers or did they make you think, discuss and debate, that is education. Guiness Drink

 

[a2]

Boys lets not start this again for gods sake.

 

[Apache]

i think when you have known the guy long enough to form a truly unbiased opinion you will realise that shakey is not ARROGANT however he does border on being BRILLIANT,but i suppose its difficult for you to comment or understand some of the technicalities of the debate as you are not a spark yourself are you.Guiness DrinkGuiness Drink

BTW don't insult my intelligence. I have 5 A levels and a bloody good degree, and I dare say more letters after my name than you

 

[Apache]

Boys lets not start this again for gods sake.

I'm sorry admin 2 - hackles went up :|

 

[sirsparkabit]

i think when you have known the guy long enough to form a truly unbiased opinion you will realise that shakey is not ARROGANT however he does border on being BRILLIANT,but i suppose its difficult for you to comment or understand some of the technicalities of the debate as you are not a spark yourself are you.Guiness DrinkGuiness Drink

We that is i believe that

even if apache isn't a spark he is a great poster and as he has to deal with life threatening situations must have a good mind ,sorry if you knew him you may say brilliant(said that without shouting) :^O