RCD splitting question

[piggyitm]

Hey guys!!
Can anyone tell me if I'm wrong.
I've run a 16mm Twin from mains to a 2 storey extension where I'm putting in a new board.2 rings 2 lights and smokes
I have to put in an RCD at the mains end so I was gonna put the new board on a 100a Main SW.
Is that Ok or do I have to still put in a Dual RCD split load to cover me for division of circuits?
Cheers

 

[High Tower]

Wrong in many ways!! Why 16mm and why twin and earth?? Have you done your calcs taking max demand and length of conductors into account, more so, you cannot supply this kind of load from a existing rcd as when combined with other circuits the rcd will overloaded and in the event of a fault the rcd would trip at the origin causing neuceince tripping at the house and leaving the occupants of the house with issues trying to get it reset.

This needs the attentions of someone with a higher degree of competence

The way to do it is split the meter tails into henly blocks into a switch fuse, swa to the flat from there, suitably sized as per calcs. This then negates the need for RCD at origin. Terminated into a split load twin RCD. Board in the flat.

 

[Deleted member 9648]

Wrong in many ways!! Why 16mm and why twin and earth?? You cant dismiss this out of hand,it may well be adequate....more info on the loading,earthing system,and installation method is required Have you done your calcs taking max demand and length of conductors into account, more so, you cannot supply this kind of load from a existing rcd as when combined with other circuits the rcd will overloaded How do you know that?and in the event of a fault the rcd would trip at the origin causing neuceince tripping at the house and leaving the occupants of the house with issues trying to get it reset.

This needs the attentions of someone with a higher degree of competence

The way to do it is split the meter tails into henly blocks into a switch fuse, swa to the flat from there, suitably sized as per calcs. This then negates the need for RCD at origin. Terminated into a split load twin RCD. Board in the flat.

I agree that an RCD at the origin is not best practice,but more info is needed on the type of earthing system...is the reason for an RCd at the origin because the earthing is TT?....or are you thinking the T/E distribution circuit will be buried and need RCD protection?
Also the OP states the distribution circuit will be on a 100a main switch....will there be any overload/fault protection for the proposed 16mm?.....A lot more info is needed here to give an answer.

 

[High Tower]

I agree that an RCD at the origin is not best practice,but more info is needed on the type of earthing system...is the reason for an RCd at the origin because the earthing is TT?....or are you thinking the T/E distribution circuit will be buried and need RCD protection?
Also the OP states the distribution circuit will be on a 100a main switch....will there be any overload/fault protection for the proposed 16mm?.....A lot more info is needed here to give an answer.

To be fair even on a TT, a split load twin RCD should satisfy the regs and would render any at origin pointless, and I get the impression he was suppling it from another 30mA on a exsisting board, hence switchfuse and henleys.

I know I should have asked for more info, to be fair I normally do! But on this occasion I was trying to avoid the normal 20 post back and forth trying to clear up the basics.

 

[Engineer54]

Hey guys!!
Can anyone tell me if I'm wrong.
I've run a 16mm Twin from mains to a 2 storey extension where I'm putting in a new board.2 rings 2 lights and smokes
I have to put in an RCD at the mains end so I was gonna put the new board on a 100a Main SW.
Is that Ok or do I have to still put in a Dual RCD split load to cover me for division of circuits?
Cheers

If this is an ''extension'' to an existing property, Why are you installing a separate CU remote from the existing CU?? If you don't have enough ways in the existing CU you could either add another below /above
existing, or change the existing CU for a CU with enough ways to cover this new extension to the property.

Having 2 remotely separated CUs in a single dwelling property is a nonsense....

 

[Deleted member 9648]

If this is an ''extension'' to an existing property, Why are you installing a separate CU remote from the existing CU?? If you don't have enough ways in the existing CU you could either add another below /above
existing, or change the existing CU for a CU with enough ways to cover this new extension to the property.

Having 2 remotely separated CUs in a single dwelling property is a nonsense....

Why??.....running a single distribution circuit to a separate local DB may be a whole lot easier than running back a shed load of final circuits to the origin.

 

[Deleted member 9648]

To be fair even on a TT, a split load twin RCD should satisfy the regs and would render any at origin pointless, and I get the impression he was suppling it from another 30mA on a exsisting board, hence switchfuse and henleys.

I know I should have asked for more info, to be fair I normally do! But on this occasion I was trying to avoid the normal 20 post back and forth trying to clear up the basics.

Well no mate....if it's a TT an RCD with be necessary at the origin to provide fault protection to the distribution circuit...ideally a 100ma time delayed with a split rcd board in the extension.....if it's a TT and thats how the OP is going to do it

 

[Engineer54]

''Why??.....running a single distribution circuit to a separate local DB may be a whole lot easier than running back a shed load of final circuits to the origin. ''


Put it this way then, ....If it was my house and you suggested running in another CU, for what is, when all said and done just an extension of my house you'd be gone!!! Two remotely separated CUs in a single dwelling is not my idea of a correct electrical installation. ....It's just an easy option!!!

 

[Deleted member 9648]

''Why??.....running a single distribution circuit to a separate local DB may be a whole lot easier than running back a shed load of final circuits to the origin. ''


Put it this way then, ....If it was my house and you suggested running in another CU, for what is, when all said and done just an extension of my house you'd be gone!!! Two remotely separated CUs in a single dwelling is not my idea of a correct electrical installation. ....It's just an easy option!!!

It depends on the size of the house obviously....but the above statement as a generalisation is misleading and incorrect....for example the two storey extension may be a separate annexe...granny flat?....in which case a separate DB would make sense. If the house was a large one running final circuits back to the origin may result in excessive final circuit legnths....a second DB would solve those issues.

 

[piggyitm]

Ok.The existing board is 15th Edition and obsolete on a TNS.The idea was to henley into the tails with some kind of RCD config to protect the cable and deal with 17th regs about 50mm depth.Is this wrong Also?The question was do i still need to divide my circuits accross 2 rcds in my new board even if it's got an rcd at the main?

 

[Engineer54]

Ok.The existing board is 15th Edition and obsolete on a TNS.The idea was to henley into the tails with some kind of RCD config to protect the cable and deal with 17th regs about 50mm depth.Is this wrong Also?The question was do i still need to divide my circuits accross 2 rcds in my new board even if it's got an rcd at the main?

Well that's a bit daft isn't it, having an 30mA RCD protecting 2 further 30mA RCDs or RCBOs!!!

So what's the plan then, leave what your calling an obsolete CU for the existing installation, and provide a spanking new CU for the extension?? So the different parts of the house will be wired to differing wiring Regs also??

Sorry, i just can't get my head around having 2 completly seperate CUs in a SINGLE dwelling house.

 

[pushrod]

Ok.The existing board is 15th Edition and obsolete on a TNS.The idea was to henley into the tails with some kind of RCD config to protect the cable and deal with 17th regs about 50mm depth.Is this wrong Also?The question was do i still need to divide my circuits accross 2 rcds in my new board even if it's got an rcd at the main?

Don't put 2 ordinary rcds on the same circuit - No discrimination.

 

[pushrod]

Is the extension functioning as part of the main house? If it is i would be more tempted to go along the lines of extending the lighting circuits and sorting out the old CU. With extra circuits for the new sockets and smokes. Just my 2 pennyworth

 

[nickblake]

Im with pushrod here if you add further cu's then they would have to be connected to the original cu or if your lucky enought to have a main switch installed as you have to provide a single point of isolation , i have installed 2 cu's in a small bungalow , but this was due to the existing cu being above a ceiling height so i installed a small main board with a 3 pole isolator then subed out the main circuits to one board and eco 7 to another , and protected by 2 63 amp mcbs , customer was chuffed as she didnt have to climb on the work tops to reset a tripped mcb

 

[Engineer54]

It depends on the size of the house obviously....but the above statement as a generalisation is misleading and incorrect....for example the two storey extension may be a separate annexe...granny flat?....in which case a separate DB would make sense. If the house was a large one running final circuits back to the origin may result in excessive final circuit legnths....a second DB would solve those issues.

First off .... It wouldn't then be a ''Single Dwelling'' house if the extension was to be an annexe or separate flat, would it?? Then you would be correct...

If this was a large house to start with, it would be very doubtful the owner would be adding a two storey extension, ....not impossible, but doubtful!! I would suggest that the now present size of house is in all probability a 4 bed-roomed house converted from a 2 or maybe even a 3 bed-roomed house. ....So how many 4 bed-roomed houses have you seen with 2 completly separate CUs supplying it's electrical needs???

I stand firmly behind my statement, ...it's certainly not misleading and it's not incorrect either. If we were talking about a very substantial 3 or 4 storey house, or of the like you could possibly have a valid point.