Sub-Mains install

[sk89dom]

Hi all, firstly I want to mention that I am qualified electrician but with no site experience. I need to install sub-mains in my garage. Currently it’s supplied view 16Amp MCB on dual RCD board inside the house. In the garages I have fused super feeding 2 sockets and light. I would like to replace 16Amp MCB to 32Amp and ran new SWA cable from main CCU. It’s PME
system so my plan is to install MCB on non RCD side and install RCBOs in the garage. Sub main is for sockets and lights in the garage and 2 circuits for 3 outside sockets and lightning circuit. Is there anything else to consider? Also I am buffled how to get that swa through the ceiling with joists crossing my route. Any advise would be appreciated. Kind regards

 

[Sharpend]

Unless you want to start drilling joists then an alternative needs to be achieved.
What location is the original CU in terms of accessibility in relation to where you need to get too?

 

[sk89dom]

Thank you for your replay. CCU is in the middle of the building unfortunately but if I ran the cable as shown on the photo it will be same direction as the joists. So no drilling required. Is my thinking correct to have MCB to sub main board exporting PME from the house. In the garage have RCBOs which some of them will be supplying outdoor equipment.

 

[ProDave]

Regardless of how you physically run the cable, I would not want a submain connected to either of the RCD's in that CU. I would be looking at shifting the whole lot left to introduce one MCB next to the main switch that is not covered by either of the RCD's and fit an RCD CU in the garage.

 

[binky]

you can avoid running swa under the floor by terminating swa into an adapatable box as you enter the house, then running normal FTE.

 

[Luckyboy]

Assuming this is a house and you have access upstairs... can you lift floorboards? If yes, then rod across to an outer wall and run T&E to a box outdoors then run SWA to the garage. Don't forget to terminate the SWA properly in the boxes so it's actually earthed.

As ProDave mentioned, you want the garage on an MCB not covered by an RCD so you may have to shift some circuits in the house CU.

 

[peterspurs]

Would the T&E not need to be on a RCD unless Mechanically protected to the out side

 

[SPECIAL LOCATION]

Would the T&E not need to be on a RCD unless Mechanically protected to the out side

Why would it?
which regulation are you thinking of?

 

[peterspurs]

Unless he can keep it 50 mm from any surface throughout as it’s new install

 

[SPECIAL LOCATION]

Unless he can keep it 50 mm from any surface throughout as it’s new install

I would expect ALL cables passing though any floor joist to be at least 50mm deep, otherwise 522.6.201 would not be met?

What's new install got to do with it...?? 50mm deep to avoid floor / ceiling fixings has been around for a long time..
Although it has been given various numbers over the years...

e.g. 522.6.100, 522.6.5, 522-06-05...
(wish they wouldn't keep re-numbering basically the same reg).

But as you didn't answer previously I will ask again..

"Why would a T&E between floors need RCD protection?
Which regulation are you thinking of?"

 

[binky]

Unless he can keep it 50 mm from any surface throughout as it’s new install

given the proposed installation route, it's very unlikely not to be 50mm away from a surface, plus there's no requirement to RCD submains or certain designated fixed appliances if the cable run allows. 522.6.202 says less than 50mm in a wall or partition (unless metallic in constuction in which case 522.6.203 applies), so I would read that as not applicable to ceiling voids or under floor voids, or attics.

 

[peterspurs]

I would expect ALL cables passing though any floor joist to be at least 50mm deep, otherwise 522.6.201 would not be met?

What's new install got to do with it...?? 50mm deep to avoid floor / ceiling fixings has been around for a long time..
Although it has been given various numbers over the years...

e.g. 522.6.100, 522.6.5, 522-06-05...
(wish they wouldn't keep re-numbering basically the same reg).

But as you didn't answer previously I will ask again..

"Why would a T&E between floors need RCD protection?
Which regulation are you thinking of?

I would expect ALL cables passing though any floor joist to be at least 50mm deep, otherwise 522.6.201 would not be met?

What's new install got to do with it...?? 50mm deep to avoid floor / ceiling fixings has been around for a long time..
Although it has been given various numbers over the years...

e.g. 522.6.100, 522.6.5, 522-06-05...
(wish they wouldn't keep re-numbering basically the same reg).

But as you didn't answer previously I will ask again..

"Why would a T&E between floors need RCD protection?
Which regulation are you thinking of?"

My interpretation of the regulations was a new install in a domestic dwelling had to have RCD protection if the 50mm deep could not be met
T&E between floors that’s part of the run up or down from ccu getting the cable outside what ever run you take keeping 50mm in a domestic is near on impossible
If I am wrong life is a learning curve
As for reg number I will look but as I said it was my interpretation of it

 

[SPECIAL LOCATION]

My interpretation of the regulations was a new install in a domestic dwelling had to have RCD protection if the 50mm deep could not be met
T&E between floors that’s part of the run up or down from ccu getting the cable outside what ever run you take keeping 50mm in a domestic is near on impossible
If I am wrong life is a learning curve
As for reg number I will look but as I said it was my interpretation of it

No one has talked about burying anything into a wall....?

As it looks to me like the CU is in a cupboard type area..

Its probably easier and neater using some surface trunking for the short distance to the CU..
Or if a suitable knock-out lines up with proposed cable position, a length of PVC conduit straight into the CU...

And with a suitable hole aligned with the floor void can go straight out onto external wall at the other end..

So dependant upon exact building structure, cable run could be done without any need for RCD protection..
certainly not impossible.

Plus as ProDave pointed out those RCD's are a bucket load of inconvenient random tripping waiting to happed with so many MCBs supplied from them.. certainly not the best design layout..

 

[David R Connell]

You have some good suggestions there!