SWA or else?

[fursdon]

25mm swa isn't a size that can be easily installed on your own over long runs so keep that in mind

Thanks for the confirmation - in old money 3-core 25mm SWA must have all the flexibility of a 1" pipe & that's my potential problem whether DIY cable-monkey or not.

Finishing and connecting 25mm SWA will also not be cheep, hence the hope of finding enough information to be able to "...discuss..." any possibility of alternative designs in 16mm (or surface mounted double-insulated) if the ultimate electrician's full design will necessitate 25mm.

The "old" CU that's for re-connection was designed & last certified at 60A, so designing a down-rating of the new supply should be theoretically possible, but until actually surveyed by the electrician that's going to do/certify the work I'm working on the possibility that changes to regs etc may only allow a down-rating to 80A - again hopefully possible through a new small "main board" at the meter-cabinet with appropriate RCD/RCBO as 60/80A control cut-out switching so that I'm left with something less than 3-core 25mm SWA to handle.

 

[shanky887614]

Thanks for the confirmation - in old money 3-core 25mm SWA must have all the flexibility of a 1" pipe & that's my potential problem whether DIY cable-monkey or not.

Finishing and connecting 25mm SWA will also not be cheep, hence the hope of finding enough information to be able to "...discuss..." any possibility of alternative designs in 16mm (or surface mounted double-insulated) if the ultimate electrician's full design will necessitate 25mm.

The "old" CU that's for re-connection was designed & last certified at 60A, so designing a down-rating of the new supply should be theoretically possible, but until actually surveyed by the electrician that's going to do/certify the work I'm working on the possibility that changes to regs etc may only allow a down-rating to 80A - again hopefully possible through a new small "main board" at the meter-cabinet with appropriate RCD/RCBO as 60/80A control cut-out switching so that I'm left with something less than 3-core 25mm SWA to handle.

if the mainswitch is rated to 60amp that is the most you will have. fuseboards are not expensive why dont you get someone to actually look a it?

 

[fursdon]

why dont you get someone to actually look a it?

That's my intention, but as I live in the boonies, I think it's only considerate to give a flavour of what I want done, to save a wasted journey to quote for a job that's either impractical or too expensive to quote for. I'm also worried that a just any implied potential for a 3-core 25mm SWA job will reduce the number of people responding (to nil?).

Hence the OP & subsequent clarification to a possible wording and the idea that new supply/main-board and existing CU are 10m apart:

"...Within the (new) meter box ... provide the tails, main switch and main distribution board ... for the installation of a domestic meter by the supplier ... suitable for the connection of new sub-mains to the existing domestic Consumer Unit and to the new 3-core 10mm² SWA external supply...."

 

[davesparks]

The time saved by using 16mm vs 25mm will be in the order of a few minutes and is a ridiculous thing to base a specification on.

 

[shanky887614]

it depends on the distance to what size cable you need.

25mm is not a large cable maybe for domestic but most pubs and comerical places have bigger supplies for example i was doing some work on a pub and was pulling 70mm cables in


25mm is around 1.6kg a m so it wont be that bad to pull in

 

[fursdon]

The time saved by using 16mm vs 25mm will be in the order of a few minutes and is a ridiculous thing to base a specification on.

The load calculations are for the electrician to calculate/certify and seem indeed to be irrelevant to the 10m cable run (25mm²) it's back to the original dilemma - will SWA be mandatory for physical protection (as I hope the existing Solar PV DNO's TN-C-S earth or separate run will meet earthing requirements ) or is there an alternatives of Double Insulated surface cable "tails" (either clipped to the surface of a roof truss or ducted with the left-over DNO underground ducting)?

 

[davesparks]

The load calculations are for the electrician to calculate/certify and seem indeed to be irrelevant to the 10m cable run (25mm²) it's back to the original dilemma - will SWA be mandatory for physical protection (as I hope the existing Solar PV DNO's TN-C-S earth or separate run will meet earthing requirements ) or is there an alternatives of Double Insulated surface cable "tails" (either clipped to the surface of a roof truss or ducted with the left-over DNO underground ducting)?

Load calculations are not irrelevant, they are the basis for selecting the cable size!

I don't understand what you mean about the PV earthing? The means of earthing will be the TNCS connection at the new supply

 

[fursdon]

Load calculations are not irrelevant, they are the basis for selecting the cable size!

Sorry Dave - didn't mean to imply the load calculations were totally irrelevant - only that (fortunately) I don't have to worry about them, so are now "irrelevant to my question" as you've convinced me that 100A/25mm is the way to go.

I don't understand what you mean about the PV earthing? The means of earthing will be the TNCS connection at the new supply

The existing barn cu & PV installation are currently connected to the original incoming supply (via house back to transformer pole) so have an existing TNCS earth circuit.

"Change of use" means that house supply and PV (both in my "ownership" on existing house-to-barn supply) remain, with only the 2 barn flats and shed re-connected separately to the new supply. The PV installation (on the barn roof) runs back via the house and will be retained by the house, including its earth circuit on the current house-to-barn supply. As the total cable distance to transformer pole will be much the same either via house or via new service cable, and as the existing barn CU is already earthed via the house, I was just wondering if the barn could be earthed to either or both, not just via the new supply.

 

[NDG Elecs]

Have scan read through this, and to me it sounds like it is all being over-thought a touch. It does not take long to gland and terminate SWA so that should not be a massive consideration in my view.

I should not imagine many electricians would be put off due to it being SWA, consideration to the route may require a labourer to assist, but it really is not that complicated.

 

[davesparks]

Sorry Dave - didn't mean to imply the load calculations were totally irrelevant - only that (fortunately) I don't have to worry about them, so are now "irrelevant to my question" as you've convinced me that 100A/25mm is the way to go.



The existing barn cu & PV installation are currently connected to the original incoming supply (via house back to transformer pole) so have an existing TNCS earth circuit.

"Change of use" means that house supply and PV (both in my "ownership" on existing house-to-barn supply) remain, with only the 2 barn flats and shed re-connected separately to the new supply. The PV installation (on the barn roof) runs back via the house and will be retained by the house, including its earth circuit on the current house-to-barn supply. As the total cable distance to transformer pole will be much the same either via house or via new service cable, and as the existing barn CU is already earthed via the house, I was just wondering if the barn could be earthed to either or both, not just via the new supply.

No you can't mix and match between two different supply earths! All earthing and bonding in an installation needs to connect to the means of earthing for that installation.
Any extraneous parts which are common to both installations will need to be bonded to at point of entry to each installation.