New Build

[BoocockP]

Hi all,

I'm due to install a mains supply to a new house. Whilst the original house was demolished we paid YEDL to relocate the meter box to a stable block building with the veiw that it could stay there to prevent having to fork out again to have it moved back to the new build. The supply fuse is 80A and we plan to run a 25mm/35mm SWA from the meter box to the utility room in the new house which is approx. 50 metres. This will be terminated in a 63A fused switch isolator and then 25mm meter tails into a split load CU. We then want to run another 16mm 40A sub main from this CU to an annex within the same new build which will terminate in a smaller CU. Can anyone see any problems with this design?

Any advise will be gladly accepted.

Paul.

 

[Spudnik]

If your tails from the intake to the utility are greater than 3 or 4 meters in length, then you should fit a switchfuse near to the intake, and run your SWA from that.

 

[BoocockP]

Thanks Jason for the prompt reply. What do you mean exactly when you refer to the 'intake'?

 

[ian.settle1]

Thanks Jason for the prompt reply. What do you mean exactly when you refer to the 'intake'?

Where the DNO supply come in.

 

[ghost]

I don't understand why you intend to install a 63A isolator when you have an 80A supply. I would always fit switchgear rated higher than your supply fuse. 63A is quite underated, particularly since you intend to supply a 40A sub main too.
Without seeing the actual job it is always a bit difficult to advise exactly what is required.

 

[BoocockP]

Hi,

The 63A switch fuse is to provide demarcation from the 80A mains supply to the submain. Please note that the supply meter box is located on an out building, not on the new build.

Paul.

If I install a 35mm SWA, in your experience, what is the easiest method of terminating it as I know most domestic CUs will only accomodate a 25mm cable. Can I terminate the 35mm in a switched fuse and then come out of that in 25mm tails to the CU?

 

[Spudnik]

Most CU main switches will accept up to 35mm tails.

Check the spec before you buy

 

[electric-ian]

99% of your loading will always be to the house.
Stick in an 80A switchfuse - maybe a wylex 110M with 80A fuse fitted then if you swa is big enough you can upgrade to 100A if you need to have the supply upped at some point.

Another switchfuse at the house end is just gonna up the cost.

Choose a make of cu thats gonna accept 35mm into the main switch.. think hager does

 

[bugsy]

If your running to a stable block additional earthing will be required ( livestock) can't remember the reg's of hand - Lenny or Jason s. will know though ! it'll just roll off ( I think they eat 7671 for breakfast!

 

[electric-ian]

Yes good point Bugsy. Ag and Horticultural premises also need to be RCD'd at source at 300mA and all sockets obviously at 30mA. I guess that applies to a stable block. { or just a 30mA main RCD }
When I did the 17th regs course, I was tought by a guy who wrote some of the regs and he recommended TT system with a bond to the floor grid for a farm job I was doing at the time.
Also had to isolate all metalwork from the tncs meter box and put barriers round it so noone could touch 2 different earth potentials before they would give me a supply..

Just looked at GN7.. TN-C-S not recommended for cattle sheds.. unless a metal grid is laid in the floor which must be bonded.

 

[BoocockP]

Thanks for the advice guys but the stable block is just being used for storage at the moment - no livestock yet.

So just to confirm my plans then: -

There is currently a meter box containing 80A mains supply fuse and isolator switch and meter. From this I have run 25mm meter tails into a second meter box (installed to give more work space) which are terminated in a Henley block. From the Henley block there is an existing 63A fused switch which go onto an existing CU in stable block and a temporary supply to a static caravan (home). From the same Henley block I plan to run a 35mm SWA (purely for volt drop as it is approx. 50 metres) underground to new building. Here I plan to terminate the SWA in a 63A fused switch and then run 25mm tails or SWA (depending on distance) to main CU in house. I then want to run a 16mm SWA from a 40A MCB in main CU to another CU in annex (granny flat). I have to drop to 63A at house to provide demarcation from 80A mains fuse to keep Mr Part P at building control happy.

Does this all sound ok to you guys?

 

[electric-ian]

Thanks for the advice guys but the stable block is just being used for storage at the moment - no livestock yet.

So just to confirm my plans then: -

There is currently a meter box containing 80A mains supply fuse and isolator switch and meter. From this I have run 25mm meter tails into a second meter box (installed to give more work space) which are terminated in a Henley block. From the Henley block there is an existing 63A fused switch which go onto an existing CU in stable block and a temporary supply to a static caravan (home). From the same Henley block I plan to run a 35mm SWA (purely for volt drop as it is approx. 50 metres) underground to new building.

Here I plan to terminate the SWA in a 63A fused switch and then run 25mm tails or SWA (depending on distance) to main CU in house. I then want to run a 16mm SWA from a 40A MCB in main CU to another CU in annex (granny flat).
Does this all sound ok to you guys?

You must put a switchfuse at the stables end of the SWA to the house

I have to drop to 63A at house to provide demarcation from 80A mains fuse to keep Mr Part P at building control happy.

Why - This makes no sense to me.
Is there a reg you are following.. ?

 

[BoocockP]

When I spoke to the Part P guy at the building control, he told me I have to provide sufficient demarcation to ensure the fuse at the house would disconnect before the 80A mains supply fuse.

 

[electric-ian]

Well.. Did you point out to him that most installations are direct on the supply fuse....

Anyway, I think you're pushing it to run the house & annexe with just a 63A capacity....
Guess you're stayind away from electricly heated showers but I suspect the house & annexe will both want to cook....I know that with diversity & all that you might never blow it but I would go with the 80A switchfuse at source and get the supply fuse upped to 100A to keep mr part p happy..
If you recently had the supply upgraded then it should be an up to date cutout so they should just change the fuse for you. Usually for free.

 

[Guest123]

I would agree with Ian about enquiry to the DNO with regard to upgrading the supply fuse to 100A.

From this isolator I would run 35mm tails into one of these 100 Amp DP Switchfuse

and link into another one as the supply terminals are doubled up enabling you to daisy chain as many as you need (within limits of course).

Re-connect your stable block feed into one of the isolators (fused accordingly), and connect your new sub-main to the house into the other one, again fused accordingly.

I might have missed it but what earthing system is present at the meter cabinet???

If there is a chance of the stables being used as such then a read of section 705 in ol' red would do you no harm at all with regard to future proofing and advising the customer.


HTH