Positioning new CU, best CU, connecting CU to meter

[Del-inquent]

Before I go into the questions, I should point out I'm not doing the work, a qualified sparky is, they just want decisions from me. They're unavailable at the moment and I refuse to be one of those customers that calls while they're trying to take a holiday. 😅

We're having our supply and meter moved. DNO and supplier consulted, without massive expense there was only one location for it to go, so a recessed box has been put in the outside wall. 

We need a new CU and a new position for it. Original plan was fused isolator in box, 10m of 25mm SWA run from meter box, under floor to inside utility cupboard. That now cannot happen as the only space it would fit is needed for something else.

Only other place I can think to put it is in the corner of our office which is very close to the meter box (2 ft away in fact).

So questions are:

Can we fit a recessed CU on an internal wall, or is it only cavity walls you can put them in? If recessed isn't an option, are there any good quality ones that look half decent surface mounted?

Both this new position or the old one require the cable to be in the cavity for a short stretch, because... well recessed meter box doesn't give much choice does it. Would you just stick with 25mm SWA even in the new close location as it's in the cavity a short distance? Any downside to keeping the SWA?

Any other general advice or thoughts accepted as I've killed way too many braincells on this job.
 

[ProDave]

What is the internal wall made of?  Stud wall easy to recess a CU, single skin brick internal wall much more challenging to recess anything.

 

The much larger job will be connecting all the circuits to the new CU.

[Del-inquent]

1 minute ago, ProDave said:

What is the internal wall made of?  Stud wall easy to recess a CU, single skin brick internal wall much more challenging to recess anything.

 

The much larger job will be connecting all the circuits to the new CU.

 
Single skin block wall. I don't mind the challenge if it means not having a big box stuck on the wall. I guess it's more a question of if it meets regs if it is recessed into a single skin internal brick wall.

The new circuits is a whole other conversation lol. I know it's going to be painful, but to be honest EVERYTHING about this "light renovation" has turned into a steaming great turd of pain and suffering. The only plus side is that the alternative new position is *almost* directly opposite the existing CU which is currently the other side of the internal wall. We need three new circuits run in, but all the ones that would be a right pita can in theory just be poked through the wall into the new box. The person that did a partial rewire in the past even helpfully left enough slack on 3 of the 4 cables to mean they'll require no effort at all!

[Dave Jones]

how far away new meter, can you not just get longer tails  and leave everything as is ?

[LiamJones]

UKPN refuse to install new/moved supplies internally now. Either an external meter box or a kiosk are the options. Your DNO may differ

[Del-inquent]

2 hours ago, LiamJones said:

UKPN refuse to install new/moved supplies internally now. Either an external meter box or a kiosk are the options. Your DNO may differ

The meter box is fitted and they’re putting the internals in, in a couple of weeks. It’s the CU that’s the issue at the moment

[Alan Ambrose]

A surface mounted CU doesn't look bad IMHO, here's ours in the hallway (and a lot less faff):

 

 

Edited March 23 by Alan Ambrose

[Del-inquent]

34 minutes ago, Alan Ambrose said:

A surface mounted CU doesn't look bad IMHO, here's ours in the hallway (and a lot less faff):

 

 

That one actually doesn’t look too bad, what make / model is it? All the ones I’ve looked at have been a bit cack looking

[TonyT]

Why have it on display!

 

at least get a recessed version and then hide it with a picture frame

 

https://www.edwardes.co.uk/products/hager-vmlf-112-spd-12-way-100-a-m-s-flush-c-unit-spd?gad_source=1&gclid=EAIaIQobChMI5p7P2vaKhQMVQY9QBh3nqw4TEAQYAiABEgLSYfD_BwE

[Del-inquent]

32 minutes ago, TonyT said:

Why have it on display!

 

at least get a recessed version and then hide it with a picture frame

 

https://www.edwardes.co.uk/products/hager-vmlf-112-spd-12-way-100-a-m-s-flush-c-unit-spd?gad_source=1&gclid=EAIaIQobChMI5p7P2vaKhQMVQY9QBh3nqw4TEAQYAiABEgLSYfD_BwE

That’s precisely what I’ve asked? From a regs perspective can you fit a recessed into a single skin internal wall, or do they have to go into an external wall?

[joe90]

How are you going to bury/protect all the cct wiring in that block wall?

[Del-inquent]

Can anyone confirm if 25mm swa is preferred to loop up and in cavity of if just some double insulated tails are okay?

[Del-inquent]

17 minutes ago, joe90 said:

How are you going to bury/protect all the cct wiring in that block wall?

Wall behind it is having most of the plaster / render taken off, and there will be a full height kitchen cupboard going in later so will be very well hidden!

 

it’s where all the current cables go anyway so half are already there 

Edited March 23 by Del-inquent

[Trojan]

A bit confused at what you mean, I take it the internal wall you're talking about is perpendicular to the meter box wall? Are you planning to chase the cables into your block wall?

 

Quote

Wall behind it is having most of the plaster / render taken off, and there will be a full height kitchen cupboard going in later so will be very well hidden!

 

it’s where all the current cables go anyway so half are already there 

 

If the cable is within safe zone on the external wall it's technically ok, if chasing though it's probably as easy to use SWA, clipping tails direct behind cabinet in zones is also ok. Fused isolator in the meter box is not a requirement if the tails are under 3m but isolator is always nice to have.

Edited March 23 by Trojan

[Del-inquent]

On 23/03/2024 at 20:31, Trojan said:

A bit confused at what you mean, I take it the internal wall you're talking about is perpendicular to the meter box wall? Are you planning to chase the cables into your block wall?

 

 

If the cable is within safe zone on the external wall it's technically ok, if chasing though it's probably as easy to use SWA, clipping tails direct behind cabinet in zones is also ok. Fused isolator in the meter box is not a requirement if the tails are under 3m but isolator is always nice to have.

yes so there’s two places the CU can go in the same corner - either on the internal leaf of the external wall, just to one side of the external meter box, or on an internal dividing wall that as you say is perpendicular to the external wall that the meter box is in. The edge of the meter box is basically at the end of the perpendicular wall, and the CU would be mounted in the corner whichever wall it is decided on, so drilling through will be in exactly the same place either way!

 

probably help if I drew a diagram out tomorrow of the two options.

 

main query is if it’s okay to sink a recessed CU into a single skin internal block wall as then it would be accessible but unobtrusive in the room. 

[Trojan]

 

1 hour ago, Del-inquent said:

yes so there’s two places the CU can go in the same corner - either on the internal leaf of the external wall, just to one side of the external meter box, or on an internal dividing wall that as you say is perpendicular to the external wall that the meter box is in. The edge of the meter box is basically at the end of the perpendicular wall, and the CU would be mounted in the corner whichever wall it is decided on, so drilling through will be in exactly the same place either way!

 

probably help if I drew a diagram out tomorrow of the two options.

 

main query is if it’s okay to sink a recessed CU into a single skin internal block wall as then it would be accessible but unobtrusive in the room. 

 

Obviously assuming this is a non load bearing wall. The hager board needs a minimum of 72mm to recess from the finished wall surface. With the 12.5mm plasterboard on each side (+ probably around 10mm each for dot and dab) you'd be right on the limit for being over 50mm from the other side of the wall assuming standard 100mm block. 

 

In reality though, good luck chasing a massive hole 50mm out of crumbly block without it falling to bits.

 

Put it in the external wall or make do with a surface mount box.

[Del-inquent]

On 25/03/2024 at 00:12, Trojan said:

 

 

Obviously assuming this is a non load bearing wall. The hager board needs a minimum of 72mm to recess from the finished wall surface. With the 12.5mm plasterboard on each side (+ probably around 10mm each for dot and dab) you'd be right on the limit for being over 50mm from the other side of the wall assuming standard 100mm block. 

 

In reality though, good luck chasing a massive hole 50mm out of crumbly block without it falling to bits.

 

Put it in the external wall or make do with a surface mount box.

Makes sense. 

This might be a really dumb question (I'm very good at those...) but is there any reason that I couldn't partially recess a Wylex CU? I was looking at what options there are on recessed CU's and happened across a thread in another group where they were discussing sinking in a Wylex, who also provide flush-fit face panels for the same boxes. If the box is okay to be fully recessed, or mounted fully surface mount, I couldn't think of any reason it couldn't be partially recessed! Only reason I am thinking of it is because the surface mount ones all have the top and bottom knockouts, and look a bit cack as a result.

[ProDave]

44 minutes ago, Del-inquent said:

Makes sense. 

This might be a really dumb question (I'm very good at those...) but is there any reason that I couldn't partially recess a Wylex CU? I was looking at what options there are on recessed CU's and happened across a thread in another group where they were discussing sinking in a Wylex, who also provide flush-fit face panels for the same boxes. If the box is okay to be fully recessed, or mounted fully surface mount, I couldn't think of any reason it couldn't be partially recessed! Only reason I am thinking of it is because the surface mount ones all have the top and bottom knockouts, and look a bit cack as a result.

I recessed a standard Hager metal CU.  The Hager one had round conduit knock outs that with it recessed come out behind the plasterboard.

 

The only real difference between a standard CU and one sold as recessed, is when you recess a standard one, you have to be accurate cutting the plasterboard around it as the front only overlaps a little.  The ones sold as recessed tend to have a larger "flange" around the front to hide imperfections.

 

 

[TonyT]

Best check your building control documents online, there are

maximum vertical and horizontal chases for walls, like 1/3 thickness can’t remember

[Del-inquent]

2 hours ago, TonyT said:

Best check your building control documents online, there are

maximum vertical and horizontal chases for walls, like 1/3 thickness can’t remember

It’s 1/3rd vertical and 1/6th horizontal - though I’ve yet to look into over what length that applies to as obviously you’d not be able to recess any box on that basis if it was absolute!
 

I assume it means over a longer cable length, rather than as a small section (otherwise you’d not even be able to sink a 35mm double socket into a 100mm block wall!)

[Trojan]

31 minutes ago, Del-inquent said:

It’s 1/3rd vertical and 1/6th horizontal - though I’ve yet to look into over what length that applies to as obviously you’d not be able to recess any box on that basis if it was absolute!
 

I assume it means over a longer cable length, rather than as a small section (otherwise you’d not even be able to sink a 35mm double socket into a 100mm block wall!)

 

How old is the wall you want to go into? If it's old breeze blocks then honestly don't bother, if it's newer style concrete blockwork you might get away with it but I wouldn't be confident in saying whether that would be compliant with building regs (at what size does a hole need a lintel etc). 

 

Electrical reg wise - as long as it's 50mm from the finished surface of the other side it's ok. 

[Del-inquent]

7 hours ago, Trojan said:

 

How old is the wall you want to go into? If it's old breeze blocks then honestly don't bother, if it's newer style concrete blockwork you might get away with it but I wouldn't be confident in saying whether that would be compliant with building regs (at what size does a hole need a lintel etc). 

 

Electrical reg wise - as long as it's 50mm from the finished surface of the other side it's ok. 

About 80 yrs old 😂

 

I’ve been debating the blocks used as they have all the look and feel of breeze blocks but for some reason they cut really nicely! Had to chase a few bits and bobs in and there and unlike any breeze block I’ve cut before, these you can get an almost polished finish on!

 

must admit I don’t fully understand the difference between cutting into a structural cavity wall and cutting into a structural internal wall. They’re both structural afterall 

Edited March 27 by Del-inquent

[Trojan]

34 minutes ago, Del-inquent said:

About 80 yrs old 😂

 

I’ve been debating the blocks used as they have all the look and feel of breeze blocks but for some reason they cut really nicely! Had to chase a few bits and bobs in and there and unlike any breeze block I’ve cut before, these you can get an almost polished finish on!

 

must admit I don’t fully understand the difference between cutting into a structural cavity wall and cutting into a structural internal wall. They’re both structural afterall 

Yeah neither do I tbh. 

On 22/03/2024 at 19:11, Del-inquent said:

 
The only plus side is that the alternative new position is *almost* directly opposite the existing CU which is currently the other side of the internal wall. We need three new circuits run in, but all the ones that would be a right pita can in theory just be poked through the wall into the new box. The person that did a partial rewire in the past even helpfully left enough slack on 3 of the 4 cables to mean they'll require no effort at all!

Another issue is that if you're removing the old CU you're potentially taking some/all of those cables out of safe zones. 

[Del-inquent]

4 hours ago, Trojan said:

Yeah neither do I tbh. 

Another issue is that if you're removing the old CU you're potentially taking some/all of those cables out of safe zones. 

Fortunately new position is almost directly opposite old CU position just on the other side of the wall, so nearly all the cables will just be poked through and remain as-is. Only really the GF ring main which will need a new chase and is being replaced anyway, so that'll go in a safe zone too

[ProDave]

28 minutes ago, Del-inquent said:

Fortunately new position is almost directly opposite old CU position just on the other side of the wall, so nearly all the cables will just be poked through and remain as-is. Only really the GF ring main which will need a new chase and is being replaced anyway, so that'll go in a safe zone too

Moving the CU to the other side of the wall and poking the cables through may well result in the cable drops no longer being in a safe zone.  Easily rectified by say putting a socket on the wall in line with the line of the cable drops.