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Topic Title: To be an RCD brd or not to be!
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Created On: 21 September 2012 01:48 PM
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 21 September 2012 01:48 PM
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bobskiwf

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Joined: 21 September 2012

,
Have replaced an old rewireable wylex brd with a RCD 6way brd (due to lack of space) this is the only brd that would fit. another electrician has been along to fit a light somewhere in the property and told the customer that the fuse board was not legal. as the circuits are protected so be it with 1 main rcd for all circuits i thought this would surfice.. am i wrong..
 21 September 2012 02:32 PM
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AJJewsbury

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It's certainly not "illegal" - the wiring regulations themselves don't have that status in law.

It may or may not comply with wiring regs (BS 7671) - section 314 demands that we 'take account of hazards that may arise from the failure of one circuit' and 'minimise inconvenience in the event of a fault' - but they're open to different interpretations. Single front-end RCDs were common place in TT installations for many years and haven't proved too troublesome. On the other hand even 'split-load' (2 RCD boards) could be argued as not complying entirely.

Another option would be a switched incomer and 1-module RCBOs - same width as your solution, but more expensive. I think most explain the pros and cons to the customer and let them decide (it's them paying for it and suffering any inconvenience after all).

- Andy.
 21 September 2012 03:17 PM
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spinlondon

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Yes you are wrong.
You've altered an existing installation that had circuits provided with individual protection into one where one device protects all the circuits.
You obviously haven't taken account of Section 314, let alone complied with the requirements.
You then I assume issued a Certificate stating that the work complies with BS7671.
The actual board isn't illegal, however issuing the fraudulent Certification most likely is.
 21 September 2012 03:31 PM
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AJJewsbury

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You've altered an existing installation that had circuits provided with individual protection into one where one device protects all the circuits.

So would I be in similar trouble replacing a BS 3036 board with a 2-RCD split load CU?

Or replacing half a dozen old 15A socket radials with one ring?

- Andy.
 21 September 2012 03:34 PM
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Legh

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Oh dear,
Expect the PC Gestapo to call when you least expect it. They'll wake you up in the middle of the night and incarcerate you in a padded cell and indoctrinate you you with the BGB or worst still the NICEIC Tech manual .... come on spin, there's no way that issuing a certificate where the limitations are stated is fraudulent

I agree with Andy.

It is not a statutory requirement to use RCDs/RCBOs on each circuit or where it impractical to fulfil 314. There are many TT systems covered by one front end RCD and in some cases PME systems. If there is no room to fit a full sized board then that is a limitation.
Its whether or not you believe it to be safe as opposed to inconvenient and there are ways around that by using EMlighting at key points in the installation if the power fails due to a tripped RCD.
Cost will be another limitation and if the client hasn't the money then one RCD is better than none.

However, a better more up to date solution, if you have the depth would have been to use RCBOs for each circuit with a DP isolator. That should silent the critics.

Legh

-------------------------
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 21 September 2012 03:49 PM
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AJJewsbury

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Expect the PC Gestapo to call when you least expect it

what? as in 'nobody expects the spin-ish inquisition' ?
sorry.
- Andy.
 21 September 2012 04:15 PM
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Legh

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Originally posted by: AJJewsbury

Expect the PC Gestapo to call when you least expect it


what? as in 'nobody expects the spin-ish inquisition' ?

sorry.

- Andy.


You've put him in a spin .....

.....amongst our weaponry are fear and surprise and the BGB.... I made that bit up,; it must be fraudulent
Cardinal the Rack, No the Cushions, no Cardinal Fang... fetch the comfy chair.
Just what i need at the moment .... thanks

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."
 21 September 2012 04:57 PM
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daveparry1

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Don't worry about it Bob, there are thousands like that around and it's certainly safer than it was before. Don't take too much notice of Spin, what he's saying is technicaly correct but I don't think he lives or works in the real world!

Dave.
 21 September 2012 05:48 PM
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Jaymack

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An emergency light or lights would not have gone awry. The customer should have been given the options available, with prices. Any assessor would probably ask some pertinent questions.

Regards
 21 September 2012 07:54 PM
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weirdbeard

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http://www.theiet.org/forums/f...id=205&threadid=25003

Hi bobski, there are some interesting opinions on this subject from some of the forum heavy- weights in the past topic above for you to read.

Personally unless the property is large and sprawling I would say in a lot of domestic places theres no problem with a front end RCD, it is very safe electrically , and I would say the person fitting the new light is a jobsworth (though i am wondering why you werent asked to fit the light! )

Assuming the customer has relayed the light fitters thoughts to you, I would discuss the situation with the customer, ask their opinion of what they want to achieve and give them some options and costs and see what the want to do.
 21 September 2012 08:11 PM
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Rulland

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As ^^^^

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Those who make no mistakes do very little work!!......
 22 September 2012 01:16 AM
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spinlondon

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This is an alteration to an existing installation.
It used to have circuits protected by individual devices, now all the circuits are protected by a single device.
Before the CU change, the installation complied with Section 314, now it doesn't.
Is it any safer now that it has RCD protection?
Or is it less safe now because a fault on one circuit will affect all other circuits?
To my mind, this is not a question of sound engineering judgement being put into practice. If it was, the OP wouldn't be on here asking their question.
This is a case of let's do what's cheapest.
To be honest with you, what is the difference in cost between an RCD and four MCBs as opposed to a main switch and four RCBOs?
As for 'limitations' on an EIC, do me a favour.
 22 September 2012 12:20 PM
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Legh

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Originally posted by: spinlondon

This is an alteration to an existing installation.
It used to have circuits protected by individual devices, now all the circuits are protected by a single device.
Before the CU change, the installation complied with Section 314, now it doesn't.
Is it any safer now that it has RCD protection?
Or is it less safe now because a fault on one circuit will affect all other circuits?
To my mind, this is not a question of sound engineering judgement being put into practice. If it was, the OP wouldn't be on here asking their question.
This is a case of let's do what's cheapest.
To be honest with you, what is the difference in cost between an RCD and four MCBs as opposed to a main switch and four RCBOs?

As for 'limitations' on an EIC, do me a favour.


Funnily enough, I do agree with you to a certain extent.
Particularly, when in a teaching environment where you would explain to learners that each circuit should be separately identified and distinct with its own overcurrent/overload protection protection and earth fault protection. This may be achieved by the use of mcbs with RCDs or RCBOs.

However, looking at 314, there is no direct reference to RCDs/RCBOs being used to provide individual earth fault protection, only that provision should be made so that nuisance tripping does not occur due to combined earth leakage currents across circuits in normal operation . This would be satisfied by one front end RCD.

As for being honest about what has been done on a certificate is not what I would call fraudulent, don't you think ?

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."
 22 September 2012 03:42 PM
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weirdbeard

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Originally posted by: spinlondon



To be honest with you, what is the difference in cost between an RCD and four MCBs as opposed to a main switch and four RCBOs?



Taking as example the legrand range from screwfix, theres a 120% price increase between a board with a 30mA switch with 4 mcbs and a main switch board with 4 rcbos, on top of that there's the increased time to install and maintain an all rcbo installation. These are austere times!
 22 September 2012 08:28 PM
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GB

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Oops all a bit heavy tonight!!
I think the general concensus is that your installation is not correct to the generally understood definition of the regs, but in no way could it be described as dangerous.
Why not put one circuit on an adjacent db with either an RCD or Rcbo? all a bit messy and certainly no less dangerous but may help others sleep better.
 23 September 2012 07:36 PM
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antric2

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Evening all,
If an NIC assessor used this as a job then you would have to use at least the top three of your best get out explainations why all dwelling is on one RCD.
Regards
Antric.
 24 September 2012 10:34 AM
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ebee

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One of the guidance notes (written by the IEE) a few years back did suggest that strictly speaking an RCD used as back up protection did not actually fall foul of this reg , however it did make quite clear that care should be considered of the implications when lumping many or all circuits on an RCD.

There was a time (not that long ago) when a front end RCD was common in new installs - Mine for example (and it`s never been a problem - Yet!).

Having said that I would nowadays do a minimum of two banks of RCDs and/or RCBOs on any install

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Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 24 September 2012 10:46 AM
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daveparry1

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Same here Ebee, i've had a front-end 30m/a rcd in place for 25 years and it's never caused any major inconvenience, and a wife and three daughters have survived it so I don't think it's caused much danger either!

Dave.
 24 September 2012 11:42 AM
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spinlondon

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With a new install, you can get away with it, to a degree.
You're not making an existing installation worse.
Yes there are thousands of installations that have up front RCD protection, which have never had a problem.
There are also thousands of installations where no overcurrent device has operated.
Perhaps we should do away with CUs, and just stick everything on one RCBO?
All protective devices are there just in case.
What we have to consider, is what will happen if the 'just in case' does happen.
Will it be more inconvenient if the lights go out because a dodgey appliance is plugged in to a socket?
Could it be a hazard?
If the answer is yes, then altering an installation so that inconveniance is increased would not comply with 314.1.
Altering an installation so that it introduces a hazard would not comply with both 314.1 and 610.4.
 24 September 2012 12:51 PM
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AJJewsbury

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Spin - are you suggesting that if an existing installation exceeded BS 7671 requirements, it would not be acceptable to alter it in such a way that it merely complied with BS 7671?
- Andy.
IET » Wiring and the regulations » To be an RCD brd or not to be!

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