Discuss Views on TT DP RCBO board up front RCD in the Electrical Forum area at ElectriciansForums.net

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rolyberkin

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What are peoples views/practice on a double pole RCBO board for a TT installation. Do you install an up front time delay RCD separate to CU or in place of main switch, in my example the tails less than 1m? Got my head in the book but am none the wiser. Cannot see the wisdom of protecting the tails, then in the process leaving tails coming out of the remote time delay RCD to the meter where there is little chance of damage?
 
Dont get much in way of TT in my neck of woods but on the few i have done further out of town I have gone for time delayed rcd in lieu of main switch. Just a matter of preference in my case and saves having a up front one in another enclosure. If you shop around there is probably little in it cost wise.
 
They are like buses around here, none for ages and now have about four lined up for CU changes, I agree I think if the tails are secured in a gland I would prefer the time delay to be in place of the main switch.
 
With your all RCBO board an upfront RCD in the isolator position is probably not necessary. It would only be protecting the bus bar, which isn't likely to be moving about.
 
With your all RCBO board an upfront RCD in the isolator position is probably not necessary. It would only be protecting the bus bar, which isn't likely to be moving about.
I would install it as a backup in case one of the RCBO's should fail in the event of a fault, I know it is unlikely but pennies for peace of mind.
 
I'd install it as a backup.

What make RCBO's are you going with? Are they single module?
 
It seems as long as the tails entry has enhanced protection,there need be no up front rcd
The way I see it,if you have a metal clad board and time delay rcd used as the main switch.
The live meter tail comes into contact with the metal,the board and all the connected cpcs carry the fault current until the cut out fuse blows

If the Rcd is mounted in a separate plastic enclosure the above fault will be disconnected by the rcd
Separate seems to offer more protection
 
I thought such an up front RCD & enclosure would be classified as similar 'switchgear', and would therefore need to comply with 421.1.201.
 
I thought such an up front RCD & enclosure would be classified as similar 'switchgear', and would therefore need to comply with 421.1.201.

This a topic that is yet to be agreed by those on high never mind us lower mortals,its the interpretation of the above that drives the decision

A consumer unit and similar switchgear , is explained in definitions as incorporating an "assembly" of fuses rcds mcbs etc
To me the stand alone rcd does not contain fuses or mcbs and is not a consumer unit prone to the melting problems that instigated this amendment


Unless someone can offer me a reasoning that is beyond my own
as to which of the 2 dangers,melting enclosure or live unprotected enclosure, is the most dangerous,as it stands I would not fit a metal enclosure for a stand alone rcd on a TT
 
This a topic that is yet to be agreed by those on high never mind us lower mortals,its the interpretation of the above that drives the decision

A consumer unit and similar switchgear , is explained in definitions as incorporating an "assembly" of fuses rcds mcbs etc
To me the stand alone rcd does not contain fuses or mcbs and is not a consumer unit prone to the melting problems that instigated this amendment


Unless someone can offer me a reasoning that is beyond my own
as to which of the 2 dangers,melting enclosure or live unprotected enclosure, is the most dangerous,as it stands I would not fit a metal enclosure for a stand alone rcd on a TT

I did seek some guidance from my schemes technical, with regard to this predicament, especially after seeing a similar set as suggested by Wylex;

To Elecsa, 'I have spoken to Wylex, and their suggestion is that a ‘common sense’ approach should be made, and that using a plastic enclosure for an RCCB before a metal CU is a lessor of the two evils, if the RCCB was to catch fire as opposed to the metal CU becoming live, but ‘we are the manufacturer’ and I should seek advice from whom I’m registered'.

Elecsa reply, 'Regulation 421.1.201 does indeed state “consumer units and similar switchgear assemblies”.

However, what regulation 421.1.201 states in full beforehand is “within domestic (household) premises, consumer units and similar switchgear assemblies shall comply with BS EN 61439-3 and shall: 1) have their enclosure manufactured from non-combustible material or, 2) be enclosed in a cabinet or enclosure constructed of non-combustible material complying with Reg 132.12”.

Whilst the data sheet you provide seems to indicate a domestic installation when you first look at it, whether or not it’s actually showing a domestic installation is something that the manufacturer needs to clarify.

However, if t is a domestic installation shown in the data sheet, I would agree with you that the separate RCCB unit would have to be in accordance with points 1 or 2 of Regulation 421.1.201'.

And, 'As I said in my previous e-mail, if the items are in a domestic installation, all the items would need to be of non-combustible construction or fitted with a non-combustible enclosure. Which option you choose is yours.

If you look on pages 32-34 in the new yellow On-Site-Guide, which is up to AMD3 , there are a number of various diagrams with different CU arrangements on TT systems, all of which are acceptable'.


There of course is the other issue, of using SP RCBO's with a TT supply; TT systems and RCBO's - https://www.electriciansforums.co.uk/threads/tt-systems-and-rcbos.110727/

Although I did read somewhere in the 18th Draft (I think) of removing this particular requirement for TT supplies. But I could just be imaging that!
 
What make RCBO's are you going with? Are they single module?[/QUOTE]

Going to fit some SBS compact double pole boards, fitted one in my own house and they are so easy to so am a bit of a convert .
 

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