RCD Protecting Twin & Earth Sub Main

[gupster]

Hi first post here, did have a search around but couldn't find previous posts that answered exactly what im after.

Had a look at a friends electrical wiring this eve and trying to advise them, as they are now unsure of the "future proofing" they have done would be compliant. (Im not a sparky but have a fair electrical knowledge so eaiser for me to ask the questions).

They have a TN-CS System with a main fuseboard in the kitchen and due to the location of the board they have run some extra cables to add submains at a later date so they dont have to get back to the main board if they want extra circuits.

Main fuse board:- Split load dual RCD

Cable to possible sub main 1:- 6mm T+E & 10mm earth to the loft so they can add another board for a future loft conversion.

5 light fittings LED
5 Double Sockets
2 x 13A Spurs


Cable to possible sum main 2: 10mm T+E & 10mm earth to boiler room.

2 x Light fittings LED
2 x 13a spur
2 x Double Sockets
1 x Water Immersion heater
Then they would like another sub-main from this to the external workshop which would be run in SWA and would have:-

3 x Double sockets
2 x Light Fittings

After they explained all this I quickly realised it was well over my head! My questions would be RCD protecting the sub mains and allowing for discrimination. And if a sub main from a sub main in this maner would be acceptable?

Thanks in advance for any help

 

[Engineer54]

One main CU and 2 sub CU's and a Garage CU, for what a standard sized house and your freinds talking about ''future proofing''?? Sounds like he missed the boat on that one when he had the main CU replaced!! Bloody ridiculous!!

 

[HandySparks]

If all the circuits are fed, directly or indirectly, from a dual 30mA RCD board with all circuits protected, then there will be no point in adding any additional RCDs anywhere else in the system. However, doing it this way may lead to inconvenience, as an earth fault anywhere will trip out about half the circuits in the house.

I'd agree with E54, the 'best' route would have been to install a CU at the origin with sufficient spare ways, say 6, and fit RCBOs to all circuits.

 

[kingeri]

What they have done is quite frankly ludicrous and totally unnecessary, unless of course they live in a mansion. If I were you, I'd simply advise them to get an electrician in next time they fancy having a go at their own electrics.

 

[Sintra]

Re: RCD Protecting Twin & Earth Sub Main

Thread now moved to DIY forum.

- - -

 

[Deleted member 9648]

Might be ridiculous but that aside there is nothing wrong with distribution circuits and separate CU's if thats how it has been done. Are these submains..(now called distribution circuits) to be fed from the main CU?...or are tails to be split and separate fused isolators?. If the latter forget RCDing the D/C's... cable intstallation methods permitting,and install sub CU's with their own RCD protection. Make sure labelling and notices at the intake clearly identify all final and distribution circuits to avoid future confusion. And yes...as long as loading and cable sizes are adequate there is no reason why the garage distribution circuit cant come from a sub distribution board.

 

[gupster]

Might be ridiculous but that aside there is nothing wrong with distribution circuits and separate CU's if thats how it has been done. Are these submains..(now called distribution circuits) to be fed from the main CU?...or are tails to be split and separate fused isolators?. If the latter forget RCDing the D/C's... cable intstallation methods permitting,and install sub CU's with their own RCD protection. Make sure labelling and notices at the intake clearly identify all final and distribution circuits to avoid future confusion. And yes...as long as loading and cable sizes are adequate there is no reason why the garage distribution circuit cant come from a sub distribution board.

Thank you very much wirepuller for the above awnser, seems like my initial questions has caused a few harsh sounding replys. To those jumping in saying they should of fitted a bigger board, an 11 way split load is allready installed for the house as this is a very large 5 bed house. And I can see why they thought this would future proof cant see a 6mm struggling with 4 - 5 sockets in a loft converted bedroom and up to 5 led lights.

The idea was to feed them from the main split load rcd protected board until i mentioned to them a nuisance rcd tripping on a sub board would trip half the house. My thought was that they would have to henly block and add another CU to power just the two sub boards with main 100ma rcd to protect the distrubuition circuit cables and give discrimination, with a 30ma in each sub board??

Thanks

 

[Badged01]

You can do whatever you want to do provided its designed correctly and meets the regulations ...... but in this instance it seems to be more of a p*ss take with CU's on CU's on CU's within a "normal house" (??).

But ultimately "wirepuller" is correct, nothing wrong with designing the most ludicrous of installation if it conforms!

 

[Deleted member 9648]

You can do whatever you want to do provided its designed correctly and meets the regulations ...... but in this instance it seems to be more of a p*ss take with CU's on CU's on CU's within a "normal house" (??).

But ultimately "wirepuller" is correct, nothing wrong with designing the most ludicrous of installation if it conforms!

^^^A bit harsh IMO^^^This argument over separate CU's in houses has been had before,personally I dont have a problem with it provided it is all properly labelled and identified...Not standard practice and not necessary I agree,but give a good reason why it is a P*ss take and ludicrous to have more than one CU in a house?
Given that the OP is faced with this scenario is he expected to tell the occupiers to rip it all out and install all final circuits back to the main CU?...

 

[SirKit Breaker]

This is quite common in older properties, i have come across a lot of installs that have had dist boards added ad hoc, because the existing one is full. The most i have ever seen is 7 in a 4 bed detached house. As wirepuller states, it is OK as long as it is all done properly.

Whatever additions/alterations you make must comply with the latest regs, so keep your wits about you, cos friends will stop being friends if and when something ends in tears.

Cheers............Howard

 

[gupster]

I think what people are forgetting is this is a very big house and that the owner had no idea what configuration would be in the loft and boiler\utility room hence the 6mm and 10mm cables. So rather than chuck a load of 2.5 and 1.5's up there they can have an option. Also the main CU is located in the kitchen a very difficult place to ever get cables back to especially due to the finish of the kitchen and the bathroom which is directly above the CU. They have cabling there ready to be used and have asked for advice on a legal, compliant solution in which I would of thought most electricians would be keen to offer advice and help.

Sounds like if a job was slightly tricky or not the norm a few of you would tell the customer to there face there install was a **** take and to rip it all out and start again. Rather than help and advise!!! Im a bit shocked to be honest. If you were to see the current install everything is perfectly to regs and no expense spared. I have just been asked to look into a few possible options for them so they dont speak to an electrician blind. Wishing I didnt choose this forum now!

Thanks you very much to the couple of you that helped. I have seen them again tonight and mentioned that the garage\workshop CU would be easy enough to get an armored from the main CU which tidys that up abit.

Is it still allowable to have a henly blocks then another board with 100ma rcd protecting the distribution circuit cables then a 30ma in the sub boards?

Thanks

 

[Sintra]

You can do whatever you want to do provided its designed correctly and meets the regulations ...... but in this instance it seems to be more of a p*ss take with CU's on CU's on CU's within a "normal house" (??).

But ultimately "wirepuller" is correct, nothing wrong with designing the most ludicrous of installation if it conforms!

Have to agree that this is a little harsh seeing as the thread had been moved into the DIY forum by the time you posted. As this is a closed forum and you have specifically asked to contribute to it then your replies must remain civil.

 

[HandySparks]

OK. It would have helped if you had said a bit more in your original post about the difficult access to the CU. We can't see the job, you can.

Are there any spare ways in the existing CU? If so, any possibility of re-configuring it to give a supply to the distribution circuits avoiding the existing RCDs?

Do the distribution circuits need RCD protection? This would generally be required if the cables run buried in the wall at a depth of less than 50mm. If they do, then a 100mA RCD won't be suitable and you will need to give them 30mA protection.

 

[Badged01]

Have to agree that this is a little harsh seeing as the thread had been moved into the DIY forum by the time you posted. As this is a closed forum and you have specifically asked to contribute to it then your replies must remain civil.

Picked the thread up from the ‘whats new’ and miserably failed to spot the DIY forum element. Wrist smacked and I’ll pay more attention next time!.

 

[AndyL]

I think what people are forgetting is this is a very big house and that the owner had no idea what configuration would be in the loft and boiler\utility room hence the 6mm and 10mm cables. So rather than chuck a load of 2.5 and 1.5's up there they can have an option. Also the main CU is located in the kitchen a very difficult place to ever get cables back to especially due to the finish of the kitchen and the bathroom which is directly above the CU. They have cabling there ready to be used and have asked for advice on a legal, compliant solution in which I would of thought most electricians would be keen to offer advice and help.

Sounds like if a job was slightly tricky or not the norm a few of you would tell the customer to there face there install was a **** take and to rip it all out and start again. Rather than help and advise!!! Im a bit shocked to be honest. If you were to see the current install everything is perfectly to regs and no expense spared. I have just been asked to look into a few possible options for them so they dont speak to an electrician blind. Wishing I didnt choose this forum now!

Thanks you very much to the couple of you that helped. I have seen them again tonight and mentioned that the garage\workshop CU would be easy enough to get an armored from the main CU which tidys that up abit.

Is it still allowable to have a henly blocks then another board with 100ma rcd protecting the distribution circuit cables then a 30ma in the sub boards?

Thanks

This depends on how the D/Cs have been run and the cables used.
If T&E buried in the wall then they will require 30mA protection at the origin
If not then no real need for the 100 mA ( as its not a TT system) just the 30mA in the CU to protect the final circuits