Supply for utility room from upstairs ringmain + a further question

[deadshort]

Hi, you may have to retain the 100ma 'upfront' and add a 30ma on your socket circuit. Your electrian will advise if the TT earth is adaquate.

DS

 

[nunesal]

Thanks for the info DS. Sorry to ask, but would I need a separate RCD for each of the upstais and downstairs socket circuits or can it be wired to cover both circuits with a common RCD?

 

[deadshort]

Don't be sorry about asking, that's the point of this site. It is not best practice to have all the sockets on one RCD. To avoid complete loss of power, and makes it easier to find a fault, it is advised that the circuits are protected by two separate RCD's.



DS

 

[nunesal]

Thanks for that DS. It is best to have the info prior to calling in a lecky.

 

[PrenticeBoyofDerry]

Hi, you may have to retain the 100ma 'upfront' and add a 30ma on your socket circuit. Your electrian will advise if the TT earth is adaquate.

This is true, that at least a 100mA upfront RCD is retained, Although there is some instances where it can be excluded, but all circuits at the board must then be covered by at 30mA RCD protection.

Thanks for the info DS. Sorry to ask, but would I need a separate RCD for each of the upstais and downstairs socket circuits or can it be wired to cover both circuits with a common RCD?

The ideal situation would be to have all circuits protected individually by RCBOs, but to comply to the regs, in your situation you need to protect newly buried cable and newly installed sockets by 30mA RCD.
As you already have an upfront RCD, it would be difficult/impossible to prevent complete loss of power if that device trips.

But it would be expected that a 30mA device would discriminate over a 100mA device.
It would be best to protect sockets circuits individually with 30mA, but BS7671 (wiring regs) could allow for them both to be on the same 30mA RCD, providing lighting circuits are not.

If you were to consider a split board with dual RCD protection, one to cover say downstairs sockets & upstairs lights, then the second to cover upstairs sockets & downstairs lights. This would require testing circuits out, to make sure this is possible and there are no shared neutrals across circuits.

This is an electricians job and will they are there, ask them to sort out youe socket circuit wiring

 

[nunesal]

Hi PBofD,

Good info that. But I may be in a slightly different situation as I also have a Granny annexe. The CU has 14 RCBO as follows:

One each: for Lighting Downstairs; lighting upstairs; (2)
One each: Sockets upstairs; sockets downstairs (2)
One each for: Shower ensuite; shower family bathroom (this one is blanked as we fitted Aqualisa gas heated/pumped system) (2)
One for Immersion (1)
Main Kitchen one each: hob; oven (2)
Garage: one (1)
Annexe: one cooker (not in use); shower; sockets; lighting (4)
Total: 14 of which 2 heavy duty ones are unused (now spare)
The annexe is now used minimally (Gran sadly passed away few years ago) as most of the family activity is in the main house.
Original house built circa 1952 and I understand the annexe was built in 1977/8 and the present CU replaced with 100mA RCD fitted circa 1998 when the main property was extended upstairs.

Would I need to fit a RCD to cover the annexe?

Thanks

 

[EFLImpudence]

RCBOs are RCDs.

 

[nunesal]

Apologies - could not come back straight away as we had a emergengy of sorts due to yesterday's heavy downpour which flooded and dislodged paving blocks on a freshly laid patio!

RCBOs are RCDs.

I meant to write the "CU has 14 'MCBs' as follows" rather than 'RCBO'. Can't believe I wrote that.

The ideal situation would be to have all circuits protected individually by RCBOs, but to comply to the regs, in your situation you need to protect newly buried cable and newly installed sockets by 30mA RCD.

However, is it possible to fit RCBOs in my situation as you suggest without changing the CU? I need to look at costings. Alternatively, any suggestions, given the 3 socket circuits I have for additional 30mA RCDs?

Thanks

 

[PrenticeBoyofDerry]

Would I need to fit a RCD to cover the annexe?

As you have a TT earthing arrangement, you have to cover the whole installation by RCD. Which I understand exists in the form of a 100mA RCD.

With regards to 30mA RCD protection, you only need to protect newly installed sockets and any newly buried cable less than 50mm in walls that was not been adequately mechanically protected, for work undertaken from 2008.
Although it is recommended that any socket outlets that can be used for external appliances, are 30mA RCD protected regardless of installation date.

 

[PrenticeBoyofDerry]

However, is it possible to fit RCBOs in my situation as you suggest without changing the CU? I need to look at costings. Alternatively, any suggestions, given the 3 socket circuits I have for additional 30mA RCDs?

A picture of your fuse board with the MCBs visible, would be helpful, as not all RCBOs are compatible with older boards.

If you cannot post pictures, details of the breakers make/model and if the CU displays a model number, that to.

RCBOs generally cost around the £30.00 (some makes cheaper, some more expensive).

You would require a competent electrician to do the device change. I would expect the electrician to fully test the installation, so it maybe cheaper to change the unit for a dual RCD board, if expense is an issue.

 

[nunesal]

Thanks PBofD,

The fuse board is MK brand, Pt No LN5500s 100A to BS spec 60 439-3 which you can just about see in top left corner of the picture. The first MCB (No 1) on the right is 32A for the hob (partially out of the pic) but can be seen in the third pic. Items 3,5 and 6 are not in use. I have also included pics of RCD and one showing the whole setup with different colour cables on the third pic. I was told that because the two colours of cables (grey and white) are obvious, there was no need to label the fact.

I hope the pics below help.

Thanks

 

[deadshort]

You can still buy rbo's for the board. You have not actually added any circuits ? You have moved a socket and replaced a damaged one. If you add a circuit or a socket the addition should have RCD protection.

DS

 

[PrenticeBoyofDerry]

Yep, RCBOs will still be available.

You can still buy rbo's for the board. You have not actually added any circuits ? You have moved a socket and replaced a damaged one. If you add a circuit or a socket the addition should have RCD protection.
DS

As would be any newly buried cable, that does not meet the existing requirement. But I also recall addition of socket outlet.

 

[nunesal]

As would be any newly buried cable, that does not meet the existing requirement. But I also recall addition of socket outlet.

Just to be clear, I have repositioned one socket from a far wall to one nearer to the origin of the take-of. The resulting extra length of cable will be clipped to the joist in the loft. The other cable's (broken) brown socket will be replaced with a new one. Both are existing circuits.

You can still buy rbo's for the board. You have not actually added any circuits ? You have moved a socket and replaced a damaged one. If you add a circuit or a socket the addition should have RCD protection.

No circuits added

As would be any newly buried cable, that does not meet the existing requirement.

By "existing requirement" do you mean the regs about permitted zones? The present layout of the cables, under 50mm in depth, follows the diagram below, as in the vertical 'light blue line' :

Thanks for your input.

 

[PrenticeBoyofDerry]

To exclude RCD protection of the cable.
All buried cable (regardless of safe zone) must be mechanically protected if not buried greater than 50mm within walls. That depth includes the reverse side of the wall. Alternatively an earth-shield cable can be used.

But there are structural regulations, concerning depth of chases, which often does not permit a chase of over 50mm.

So regulations are any new sockets and any newly buried cable, that is not buried at a depth greater than 50mm that is not mechanically protected, requires a 30mA RCD.

I do not know how many times I have to repeat this, I really think you should consider getting in an Electrician, as tests will be required.