ADS

[spinlondon]

Yes Plumber, I thought you said you were going to change that signature?

 

[Chr!s]

Yes Plumber, I thought you said you were going to change that signature?

LOL- so i did, any suggestions? be nice

 

[Manator]

Gentlemen I can understand why sidewinder is reluctant to post why any installation can be designed and engineered without the requirement for RCD,s even TT can be engineered so that a RCD is not required.

Just the same as generic maximum demand is so far off actual demand it beggers belief.

BS7671 actually has a statement that makes all your assumptions of what a RCD does void.

I can not for the life of me relay that statement as I do not have the BRB with me.

I can give the "outline" but would prefer to state word for word, which I can not given my location.

Maybe some one can do that for me?

 

[Sidewinder]

Manator,

Would love to mate, but no brb either to hand sorry.

 

[Chr!s]

Gentlemen I can understand why sidewinder is reluctant to post why any installation can be designed and engineered without the requirement for RCD,s even TT can be engineered so that a RCD is not required.

But im not suggesting there's no alternative, Just stating an RCD may be used for ADS.

 

[Sidewinder]

Canoe,

Doubt Manator can remember that either.

I only ever knew one guy who could cross ref. pg no.'s & regs etc. to that level.

KME knows him too he is a walking regs book, has taught it for years and still does.

I had a question one day, could not remember the reg, knew it was there and could not find it, was short of time as I had to explain to the customer on site why, had regs book with me.

Rung this guy, gave him the scenario & he said check reg no xxx.

FFS it was there!

I don't mean like see chap 45 or reg 454 but it was like check reg 454.1.3 or the like, and this was an obscure Q.

On my last assessment my AE pulled me on a swimming pool job.

TN-C-S/PME presntation. Remote pool house, sub main board etc.

He pulled me on an earting reg. quizzed me I could not think of it, it took him an hour to find it whilst we were driving around the jobs.

IMHO this reg was so obscure!

I'll try to dig my book out over the next few days & skim the relevant areas.

If I come up with anything I'll post it.

 

[Watchdog]

Plumber - could you please try to use the forum's quote feature properly. To quote a single post click the word quote on that post. If you wish to quote multiple posts then you can use the multi-quote button (to the right of the word quote), select all the people you want to quote and then click post reply.

It's not hard and it simplified who you are talking to without having to trawl back. You will see that by quoting properly you can see who said the initial comment and click the small blue arrow and be taken directly to their post.

 

[Doc Hudson]

I would just like to say thank you gentlemen for some interesting debate. This is one of the strong points of the forum. Not just simple answers to questions, but a bit of deeper debate about the interpretation of various aspects of BS7671. A consideration I would like all to keep in mind is, when composing your posts and assessing interpretation of particular regulations; Please remember there can be significant differences between applications of regs in domestic, commercial, industrial installations etc. Some of our members may be answering specifically from a domestic perspective others from commercial, industrial etc. These can be areas where apparent disagreements may arise? for example I can think of situations in industrial where ADS could be positively dangerous and not a safety feature. Once again thank you gents and keep the debates healthy robust and polite.

Doc H.

 

[Larnacaman]

Very true Doc, those primarily involved in domestic, have little idea of what goes on in the wider world of contracting. Where BS 7671 is manipulated, even ignored to the Contractors benifit, by there design and site Electrical Engineers, but will still comply electrically and be of a high standard. So long as the engineering etc have been signed by the responsible Qualified Engineer, in exactly the same way he would sign off his Engineering following the Regs to the letter, everything is perfectly fine...

As been stated by others here, TT systems can most certainly comply without the need of RCDs. But alas, not with the general standard of installing TT systems of today, and certainly not with a single Rod!!!.... Far too many are relying on RCD devices and ignoring the basics of an installations needs/requirements.

Applying BS7671 to every situation, and to every enviroment is almost an impossible quest. Like most laws and regulations , there is no such thing as fit all document, it will always need adapting, tweaking and whatever, to get the best desired results!!!

 

[PaulSC]

Am I missing the point here?

Surely an RCD will be about as useful as a chocolate teapot in the event of a Line to neutral fault, which a fuse or MCB will interupt very quickly assuming R1+R2 values are met for the appropriate device.

As Larnacanam said, nothing more is needed for basic ADS to function as long as the circuit has been designed correctly in the first place.

Back onto my fence ....

 

[spinlondon]

ADS is used for a a fault of negligable impedance between the Line conductor and an exposed-conductive-part or a protective conductor in the circuit.

A line to neutral fault doesn't really apply.

As for designing the circuit correctly in the first place, how would you set about designing a circuit where the Ze is between 100 and 200ohms?

 

[sellers]

can we have a re-cap of what we're debating here because its gone round and round, and I got lost!

Are we depating if an RCD is a protective device? Which it is. Are we debating that an RCD isn't part of ADS which it is! Or is it something else?

 

[ADS]

Am I missing the point here? ......in the event of a Line to neutral fault, which a fuse or MCB will interupt very quickly assuming R1+R2 values are met for the appropriate device.

...

Is this sentence not a contradiction in itself? - or have I read it wrong?

What have R1 + R2 values got to do with MCB operation during a Line to Neutral fault?

 

[PaulSC]

Spin,

My point, badly made, was that the RCD wouldn't see a Line to Neutral fault so couldn't really contribute in that scenario to ADS.

Yes, I agree, RCD's can contribute to ADS, although perhaps kicking in before the fuse or MCB would operate with regards to an earth fault. However, disconnection would still be achieved even without the RCD being present.

Don't know if thats put it back on topic. Don't even know if I'm right. :C

Paul

 

[spinlondon]

We were discussing ADS (not the member).

The discussion then moved to whether an RCD can provide ADS....

 

[PaulSC]

I'll get my coat ...

 

[sellers]

411.1 Automatic Disconnection of supply is a protective measure in which:

i) basic protection is provided by basic insulation of live parts or my barriers or enclosures, in accordance with section 416, and

ii) fault protection is provided by protective earthing protective equipotential bonding and automatic disconnection in case of fault, in accordance with reg 411.3 to 411.6

Where this protective measure is applied, Class 2 equipment may also be used.

Where specified the requirements for additional protection shall be provided by an RCD having the characteristics specified in regulation 415.1.1

411.4.4The following types of protective device may be used for fault protection:

i) An overcurrent protective device

ii) An RCD

note: Where and RCD is used for earth fault protection the circuit should also incorporate an overcurrent protective device in accordance with chapter 43

Basically there is no 1 thing that acheives ADS!! ADS is as it says on the tin, automatic disconnection of supply.

Every installation differs! They need different items to acheive ADS! Your standard TNS with an MCB won't acheive ADS if there is no supplimentary bonding on exposed conductive parts in the event of a fault on that part, same applies to your TT system that won't achieve ADS in the case of an earth fault with no RCD. If your Zs times aren't met you may not acheive ADS!

ADS is the whole shebang! Bonding, fusing, cable length, rcd's, insulation of live parts, class 1 and class 2 items, the whole chuffing thing!

:Salute

 

[Chr!s]

|

ADSi (Basic protection by) - Insulation of live parts, or barriers or enclosures.

ii (Fault protection by) - (1)Protective earthing, (2)protective equipotential bonding, (3)automatic disconnection.

(3) Automatic disconnection may be achieved by a Fuse, Circuit Breaker or RCD.

Two areas people seem to get confused with, (1) A RCD may be used for automatic disconnection, and (2) protective equipotential bonding is part of ADS.

Hope that helps

Sidewinder,you have just thanked sellers for his post which is the same as my post to which you said was no help? :|

 

[spinlondon]

That bloomin' signature!

I did try to warn you.

 

[Sidewinder]

Plumber,

Once again you have misquoted.

You have been warned / advised by the mods about this.