Cable from Meter to CU

[frank999]

Hi,
Can someone advise ... a domestic flat conversion (less than 70 kva), the CU may be sited 7mt away from a meter, the cable would need to be run up a wall through a floor and up to the CU
1) Can the cable be 16mm singles in a wooden enclosure (12mm ply) running up the wall in a bathroom, or should it be inside metal trunking, or should it be armoured.
2) The CU may be sited in an alcove just off the loft stairs - accessed by a small ladder (similar to those found on a bunk bed). This alcove is directly adjacent and beneath an incoming feed from a 3kw solar panel supply, where an inverter will also be installed.

Any comments on the viability of this appreciated.

 

[EFLImpudence]

Well, I hope it is less than 70kVA. Did you mean 70 Amps?

Assuming a 'normal' supply of 80A, then 16mm² would be adequate.

1. if the cable is concealed(not apparent) anywhere in the run then armoured would be better.

2. The CU should be comfortably accessible.

You will require a switch fuse at the meter.

 

[flameport]

Can the cable be 16mm singles in a wooden enclosure

No, singles need to be contained in trunking or conduit. A plywood enclosure is not suitable.
Assuming that by 'singles' you actually mean what they are - single insulated wires.

 

[conny]

Well, I hope it is less than 70kVA. Did you mean 70 Amps?

Assuming a 'normal' supply of 80A, then 16mm² would be adequate.

1. if the cable is concealed(not apparent) anywhere in the run then armoured would be better.

2. The CU should be comfortably accessible.

You will require a switch fuse at the meter.

Just curious, if it was a 100A supply would you be best to uprate to 25mm or is 16 still suitable?

 

[plugwash]

Generally, single insulated cores must be installed inside suitable conduit or trunking, insulated and sheathed cables (including the double insulated single cores used as "meter tails" nowadays) don't.

However there is an additional complication, the cable supplying the CU will not be RCD protected. Since the 17th edition there are additional requirements for non-rcd protected concealed cables. While there are theoretically several ways to comply with these requirements, the most practical tend to be either armored cable or earthed metal conduit/trunking.

Furthermore many DNOs insist that the customer provide their own over current protection within a short distance of the meter.

Afaict the usual solution to siting a CU remotely from the meter nowadays is to run the tails from the meter to a switch fuse, then run armored cable to the CU.

 

[EFLImpudence]

Just curious, if it was a 100A supply would you be best to uprate to 25mm or is 16 still suitable?

According to BS7671 you would require 25mm² - although DNOs use 16mm².

 

[frank999]

Thanks for all the replies.

Are we saying that where armoured is not clipped to the outside of a wall (ie hidden or boxed away) then that also needs to be in metal conduit or trunking ?

16mm meter tails in metal trunking would suffice though.

Metal vs ply makes sense, a drill bit would go straight through ply. rermember now reading about tests for 'penetration' of enclosures and trunking.

"The CU should be comfortably accessible"

Some CU's end up under the stairs, necks bent double to see anything, anywork in that area requiring knee pads ... any more detail on what is defined as 'comfortably accessible'.

All new 2.5 and 1.5 has been cut ready for the CU to go into this particular space, if we changed minds and it went next to the meter, is there any issue extending the cables with connection boxes behind an access panel, does the access panel need to be closed using screws ? not ideal extending cables like that I'm sure, but would prefer not to rip out newly laid cable.

 

[winston1]

W

Thanks for all the replies.

Are we saying that where armoured is not clipped to the outside of a wall (ie hidden or boxed away) then that also needs to be in metal conduit or trunking ?

16mm meter tails in metal trunking would suffice though.

Metal vs ply makes sense, a drill bit would go straight through ply. rermember now reading about tests for 'penetration' of enclosures and trunking.

"The CU should be comfortably accessible"

Some CU's end up under the stairs, necks bent double to see anything, anywork in that area requiring knee pads ... any more detail on what is defined as 'comfortably accessible'.

All new 2.5 and 1.5 has been cut ready for the CU to go into this particular space, if we changed minds and it went next to the meter, is there any issue extending the cables with connection boxes behind an access panel, does the access panel need to be closed using screws ? not ideal extending cables like that I'm sure, but would prefer not to rip out newly laid cable.

What is the 1.5 for? Too big for lighting, too small for power.

 

[John D v2.0]

Are we saying that where armoured is not clipped to the outside of a wall (ie hidden or boxed away) then that also needs to be in metal conduit or trunking

No, armoured can be buried, it won't have rcd protection hence needing to be armoured.
If it's plainly visible on the wall it can be standard meter tails. The conduit would be necessary if you needed to mechanically protect the cables against knocks and damage.

Some CU's end up under the stairs, necks bent double to see anything, anywork in that area requiring knee pads ... any more detail on what is defined as 'comfortably accessible'.

Doesn't sound accessible.
For new houses or conversions it would have to be about 1400mm from the floor so it's accessible for people with limited mobility, part M. For refurb or rewires use your common sense, but you should at least be able to see it and work on it with both hands and a head torch for a reasonable period of time eg half an hour, without pain. However if you don't keep to that no one will do anything to stop you.

is there any issue extending the cables with connection boxes behind an access panel, does the access panel need to be closed using screws ?

No issue as long as it's in a proper terminal box, should require a tool to open it, so it could be closed with screws, zip ties or whatever.

 

[JohnD]

Too big for lighting

no it isn't.

 

[John D v2.0]

W

What is the 1.5 for? Too big for lighting, too small for power.

Really? It's fine for both! You can easily run a socket eg boiler circuit off 1.5. And most of our lighting is on 1.5 too.

 

[winston1]

Really? It's fine for both! You can easily run a socket eg boiler circuit off 1.5. And most of our lighting is on 1.5 too.

Only 1.0mm is required for lighting. You have wasted money.

 

[John D v2.0]

Only 1.0mm is required for lighting. You have wasted money.

If you say so! In reality we got money off the house in part because the electrics were fitted in the 70s and had a lot of more recent bodges. Rewiring the whole lot would have been the waste of money.

 

[Risteard]

Only 1.0mm is required for lighting. You have wasted money.

LOL. Not sure what you'd make of the Energy Efficiency chapter...

 

[conny]

Only 1.0mm is required for lighting. You have wasted money.

Approximately 6.5p per metre based on SF prices.
I'm sure that's not going to break his bank balance.