IET logo
 
IET
Decrease font size
Increase font size
Topic Title: Using an RCD as the main switch!
Topic Summary:
Created On: 10 July 2008 01:39 PM
Status: Post and Reply
Linear : Threading : Single : Branch
<< 1 2 3 4 Previous Next Last unread
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 12 October 2012 11:29 PM
User is offline View Users Profile Print this message



Zs

Posts: 2977
Joined: 20 July 2006

Sorry to drag an old thread to the top but troubling to cut and paste well.

Originally posted by: OMS

think i've read somewhere that I cannot use an Rcd as a main switch other than on a TT system.So installing a D/B with just a 30ma RCD acting as a main switch also is a not an option!




Two seperate issues I think.



1 - can you use the RCD as a main switch for the installation - yes, all RCCB's that meet BS EN 61008 are rated for isolation.



2 - should you be using a single front end RCD - again probably yes. BS 7671 imposes on a you a requirement to avoid danger and minimise inconvenience. OMS



Do it! It's easier to get forgiveness than permission


Can anyone point me to where that sentence 'to avoid danger and minimise inconvenience' is please.

Not disputing BTW, I'm checking my facts for peace of mind and this quote is from a thread from 2008 so it may be out of date. But I like it. I was challenged by a wylex rep this afternoon whilst trying to buy a small DB with main switch and a separate RCD. He was telling me I didn't need a main switch. I didn't fancy the bus bar on the wylex one so was asking for my usual hager. Won't bore you, but V dodgy series of faults to correct including reverse polarity on half the sockets and 85V tap to shower screen.. Worst for ages. A chance that I wouldn't get it all done by close of play so I needed the option to bypass anything remotely RCD for the night.

It P's me off being put down in public. Wholesaler full of my mates and I'm stood there saying 'Oh, I'll have a look at that, thank you so much' and thinking 537/411/Tables 41/ you wannna have a look at my touch voltage right now you twit/ etc..

Sorted by 8pm. RCD holding up a treat on that old Rubber cable....

You still up? BBC4 right now, Go on, it'll make you smile.

Zs
 12 October 2012 11:49 PM
User is offline View Users Profile Print this message


Avatar for Legh.
Legh

Posts: 3498
Joined: 17 December 2004

Good evening Zs,
You need to look in Spinlondon's magic book of fun or alternatively, try 314.1(i)
Be assured there is nothing there relates directly to the use of RCDs..

Nothing like Squeeze. Some good stuff on BBC 4 Friday eve at the moment....

Legh

-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 13 October 2012 12:29 AM
User is offline View Users Profile Print this message



Phillron

Posts: 1212
Joined: 18 January 2007

There you go Zs
314.1 (i)
 13 October 2012 01:17 AM
User is offline View Users Profile Print this message


Avatar for spinlondon.
spinlondon

Posts: 4439
Joined: 10 December 2004

Originally posted by: Legh
You need to look in Spinlondon's magic book of fun or alternatively, try 314.1(i)
Be assured there is nothing there relates directly to the use of RCDs..

Does there have to be?
Is there anything there that directly relates to MCBs, or fuses?
It does mention something about minimising inconvenience in the event of a fault, which to my mind would cover all types of protective devices.
Now it may be, that you personally don't think it would be inconvenient if all the circuits in an installation are de-energized because one has developed a fault.
Perhaps you don't consider that it's inconvenient for someone to be laft with no heating, lighting hot water or even a means to make a cup of tea, because a bit of damp got in and now the RCD's tripped.
Considering that the majority of electrical appliances used in a domestic installation, are there for convenience, I find it a bit odd that you consider having to do without them would not be inconvenient.

I think that if you asked 100 members of the general public, they would all say that they would consider it inconvenient.
 13 October 2012 01:11 PM
User is offline View Users Profile Print this message


Avatar for Legh.
Legh

Posts: 3498
Joined: 17 December 2004

Originally posted by: spinlondon

Originally posted by: Legh

You need to look in Spinlondon's magic book of fun or alternatively, try 314.1(i)

Be assured there is nothing there relates directly to the use of RCDs..


Does there have to be?

Is there anything there that directly relates to MCBs, or fuses?

It does mention something about minimising inconvenience in the event of a fault, which to my mind would cover all types of protective devices.

Now it may be, that you personally don't think it would be inconvenient if all the circuits in an installation are de-energized because one has developed a fault.

Perhaps you don't consider that it's inconvenient for someone to be laft with no heating, lighting hot water or even a means to make a cup of tea, because a bit of damp got in and now the RCD's tripped.

Considering that the majority of electrical appliances used in a domestic installation, are there for convenience, I find it a bit odd that you consider having to do without them would not be inconvenient.

I think that if you asked 100 members of the general public, they would all say that they would consider it inconvenient.


I suppose thats logical and there is reference to control and protection of individual circuits in 314.2 and maybe applicable in certain situations.
However, RCCB single switched isolation in TN systems are there primarily for additional protection and TT to provide the necessary earth fault protection.
So at present its a design consideration as to whether one provides additional protection to all circuits where overcurrent and short circuit faults are covered by individual protective devices.
As said elsewhere, I think that the use of double pole RCBO protection providing all round discrimination on each circuit particularly in domestic environments is as close as one is going to get to a 'perfect' design solution. As long as we maintain and test for 411.1 and 411.3.

Legh

-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 13 October 2012 01:17 PM
User is offline View Users Profile Print this message


Avatar for Paradigm.
Paradigm

Posts: 700
Joined: 10 September 2010

Originally posted by: spinlondon

I think that if you asked 100 members of the general public, they would all say that they would consider it inconvenient.


Since the word "inconvenient" is subjective and cannot be defined as a one size fits all answer, that above comment is meaningless and totally presumptuous. Unless of course you have some empirical data from a survey that's been carried out..............


Nick

-------------------------
"be careful of what you write"
 13 October 2012 04:02 PM
User is offline View Users Profile Print this message


Avatar for spinlondon.
spinlondon

Posts: 4439
Joined: 10 December 2004

I think that you didn't think before you posted.
What do you think?
 13 October 2012 07:13 PM
User is offline View Users Profile Print this message



weirdbeard

Posts: 1579
Joined: 26 September 2011

Originally posted by: spinlondon


Perhaps you don't consider that it's inconvenient for someone to be laft with no heating, lighting hot water or even a means to make a cup of tea, because a bit of damp got in and now the RCD's tripped.
.


My question is where and how has the damp got in? Is there equipment installed that is not suitably rated for it's environment? Has properly selected equipment degraded through lack of maintenance, or suffered from unforseen damage that allows the ingress? - I don't believe the regs make allowances for such situations.



I think that if you asked 100 members of the general public, they would all say that they would consider it inconvenient.


If your question to those 100 people mentioned that when a 30mA RCD trips there is sufficient current to cause death flowing to an unintended path, I think there would far fewer than your estimate who would consider it inconvenient.
 13 October 2012 11:52 PM
User is offline View Users Profile Print this message



Zs

Posts: 2977
Joined: 20 July 2006

Thank you for finding the mystery sentence for me.

My tuppeny worth is that inconvenience is a key word and it is open to interpretation. I would not have left my clients without basic comforts and agree with Spin. We make a judgement on the best way forward on behalf of our clients and mine was to be ready to remove a couple of RCD tails for a night or two. Hence being lambasted by a wylex rep eager for me to buy an RCD main switch and a less convenient busbar.

Certainly yesterday I could foresee massive inconvenience across the entire house were I not able to omit RCD protection while the various faults and serious dangers were sorted. I could see possible dabbling after hours by the homeowner (who knows a man who knows a man who would tell him to remove neutrals from the bar etc.), and I could see my own inconvenience going back and forth to a board with an RCD which wouldn't hold while I was fault finding and Z testing. The luxury and finesse of RCD protection, in this case, was reserved for after correction of the death traps. They'd not have been able to afford RCBO. This was an unexpected three days for them as it is.

I can also foresee the convenience of a dedicated freezer circuit in that house, dedicated smokes and so on.

So, a nice adaptable DB, future proofed with a pleasing basic busbar and a comforting clunk as the mechanical main switch is operated. That's something you don't get with an RCD; the sound and feeling of disconnection/connection which a 60947-3 has to offer.

I finished it today and whilst they need a great deal more work, the immediate dangers are gone. They have an RCD as precursor to more problems in the future, which I can deal with as and when they can afford it and they need never be without the whole house electrics because I can now transfer a circuit onto a non rcd protected way and at least give them something. Job's a goodun.

Zs

Edited: 13 October 2012 at 11:59 PM by Zs
 14 October 2012 10:07 AM
User is offline View Users Profile Print this message



Jaymack

Posts: 4677
Joined: 07 April 2004

It's easier to let the person who is paying to such decisions for a common RCD or not; after the options with costs have been given in writing, and where no rules are being broken. There is always the suspicion with some that unnecessary work/cost is being created.

The problem mainly arises with a DB change and existing circuits.

A power supply can never be guaranteed, but there are backup options, usually not for a domestic consumer.

1. For a common lighting or socket circuit, would you split these circuits across RCD's?

2. Would you consider emergency lighting for a common circuit?

3. Would you highlight the increased danger to family or carers of infirm persons, of a common lighting circuit where infirm persons are concerned?

4. Would you highlight the inconvenience of common lighting and/or power circuits for all?

5. Thankfully, it's becoming a situation of the past, but tungsten lamps cause tripping MCB's of type B. How many customers would opt for changing the MCB to a type C?

Regards
 14 October 2012 01:09 PM
User is offline View Users Profile Print this message



weirdbeard

Posts: 1579
Joined: 26 September 2011

Originally posted by: Zs

I was challenged by a wylex rep this afternoon




A wylex rep should be pretty easy to deal with:

"Who is it you work for again? I can't quite RECALL!"

"Oh wylex is it.... Got any hot deals at the moment?... and I don't mean mcbs that catch fire...."

etc
 15 October 2012 04:13 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19747
Joined: 23 March 2004

You still up? BBC4 right now, Go on, it'll make you smile.


- It did

I was challenged by a wylex rep this afternoon whilst trying to buy a small DB with main switch and a separate RCD. He was telling me I didn't need a main switch.


Theoretically you don't - but having had to totally and utterly lash up a DB recently because the RCD main switch had gone a bit oingy boingy and I was away from home for the week, it really is a pain in the a**e

Hence being lambasted by a wylex rep eager for me to buy an RCD main switch and a less convenient busbar.


He should work on his customer care skills - next time you see him, mention inconvenience and fault finding on pre existing installations that have a number of (from the sound of it) pretty nasty faults. Or without being a brand snob - just remind him he works for Wylex - they are not exactly at the cutting edge of switchgear technology

I guess the one thing you could say in favour of a single front end RCD, though -

despite the best efforts of those certain gentlemen who don't believe the missus when told "I've just had a shock" and usually also own a neon screwdriver and are willing to "have a look"-

they will almost certainly remove all electrical risk no matter how hard he fiddles - and the power ain't coming back on - foolproof in a dodgy installation - but hugely inconvenient, which is not always a bad thing -

Right - black coffee in bed, I think -

OMS

-------------------------
Failure is always an option
 15 October 2012 04:45 PM
User is offline View Users Profile Print this message


Avatar for Paradigm.
Paradigm

Posts: 700
Joined: 10 September 2010

Originally posted by: spinlondon

I think that you didn't think before you posted.

What do you think?



I think, therefore I am........................ apparently??????

Nick

-------------------------
"be careful of what you write"
 15 October 2012 05:39 PM
User is offline View Users Profile Print this message


Avatar for spinlondon.
spinlondon

Posts: 4439
Joined: 10 December 2004

Do you have any empirical data to support such a hypothesis, Nick?
 15 October 2012 06:02 PM
User is offline View Users Profile Print this message


Avatar for Paradigm.
Paradigm

Posts: 700
Joined: 10 September 2010

No Spin, its just something I made up to make my position look good

Nick

-------------------------
"be careful of what you write"
 15 October 2012 06:30 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19747
Joined: 23 March 2004

Originally posted by: Paradigm

No Spin, its just something I made up to make my position look good

Nick


Have you tried consultancy, Nick

Regards

OMS

-------------------------
Failure is always an option
 15 October 2012 06:33 PM
User is offline View Users Profile Print this message


Avatar for spinlondon.
spinlondon

Posts: 4439
Joined: 10 December 2004

Originally posted by: Paradigm
No Spin, its just something I made up to make my position look good

Nick


Since the word "good" is subjective and cannot be defined as a one size fits all answer, that above comment is meaningless and totally presumptuous. Unless of course you have some empirical data from a survey that's been carried out..............
 15 October 2012 08:06 PM
User is offline View Users Profile Print this message



weirdbeard

Posts: 1579
Joined: 26 September 2011

In a recent survey, 100% of respondants thought that unless spinlondon had taken measures to provide an automatic alternative supply in the event of a network supply failure he had failed to comply with BS7671 regulation 131.7 which comes under the heading 'Fundamental Principles', so by certifying ANY installation without this facility he is surely commiting fraud!
 15 October 2012 08:21 PM
User is offline View Users Profile Print this message


Avatar for Legh.
Legh

Posts: 3498
Joined: 17 December 2004

Originally posted by: spinlondon
Originally posted by: Paradigm
No Spin, its just something I made up to make my position look good
Nick


Since the word "good" is subjective and cannot be defined as a one size fits all answer, that above comment is meaningless and totally presumptuous. Unless of course you have some empirical data from a survey that's been carried out..............


Lol, perhaps a reminder will help. Some reality might help ?

I think that if you asked 100 members of the general public, they would all say that they would consider it inconvenient.


Now there is an advert on the TV which suggests that 8 out of 10 cats prefer Wiskers. Well we know this is more or less rubbish since my proof is that my three cats prefer Kitty-Cat. And that is a fact as far as my cats are concerned....

I know they'd prefer fresh fish heads but they're not getting it without me going fishing and that's about as realistic as me commanding the Starship Enterprise.

But then that's only three cats out of three !

Legh



-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 15 October 2012 09:02 PM
User is offline View Users Profile Print this message


Avatar for Paradigm.
Paradigm

Posts: 700
Joined: 10 September 2010

Originally posted by: OMS



Have you tried consultancy, Nick



Regards



OMS


I think I'm a natural OMS, it just flows out on its own

N

-------------------------
"be careful of what you write"
IET » Wiring and the regulations » Using an RCD as the main switch!

<< 1 2 3 4 Previous Next Last unread
Topic Tools Topic Tools
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.