Incoming size cable ??

[NCSPARKY]

Hi everyone,

On a job at the moment and trying to
Work out cable size needed for property supply. Lots going on and struggle to work out potential loads of new build not built yet.

Loads
2 x ring main around 15 sockets

Lighting circuits consisting of around 60 spotlights and outside lighting

Electric heating system been told is 32a.

Induction hob or no amp hob not been specified, will go
Induction for worse case

Kitchen ring and circuit for usual appliances

it is a 4 bed house about to be built but they are not massively clear until walk round with client once build is at first phase.

Going off calculations of what I’ve done so far on rough info I’m estimating a 35mm SWA.

There is a green cabinet at front of driveway and is a TT system l, 60a main fuse, and is going to be about a 50metre run ducted in the ground.

No grief please.

Thanks

 

[pc1966]

60A, 50m and 35mm^2 is not quite adding up to me!

Start by putting down each circuit in a table, what the loads are, and for domestic stuff use the OSG diversity values in Appendix A to get an idea of max demand.

Electric heating, and to some extent instant showers, are where you will really have big and sustained demands.

 

[NCSPARKY]

Yeah I know this is what the DNO have put in place just a supply with a 60a cut out and then to the meter.

 

[westward10]

If there is associated parking you must make provision for EV charging.

 

[UNG]

Yeah I know this is what the DNO have put in place just a supply with a 60a cut out and then to the meter.

The DNO doesn't just put a supply in which then begs the question who ordered / requested that supply with the limited demand it gives

 

[NCSPARKY]

The DNO doesn't just put a supply in which then begs the question who ordered / requested that supply with the limited demand it gives

Yes I agree, in the mean time I am going to contact the DNO and see if they can come and upgrade the fuse/supply to the land. Then I suppose just do my calculations and run the cable it’s going to need to the property

 

[timhoward]

Is the 32amp electric heating a heat source pump? I’m not up to speed on latest requirements but you may have to request permission from DNO for installation.

Before talking to DNO you need to work out the max demand with diversity, as advised in above posts.

 

[pc1966]

Some of the DNO offer advice on property "After Diversity Maximum Demand" calculations, for example:

https://www.spenergynetworks.co.uk/pages/admd_calculator.aspx

 

[timhoward]

I want to throw another thought in.
If you are putting in ducting anyway (i.e. the hard bit) I'd compare the price of 50m of 25 sq mm SWA (guessing the required size) and associated aggro with asking the DNO to move the service head.

I've arranged several similar service head moves and was extremely nervous about the first one but it's actually easy. The client fills out a form, the DNO drops off ducting, a meter box, and a hockey stick, the builder fits the meter box and the ducting, and the DNO turn up with two blokes, one joints it and the other fits a head, meter and isolator, usually taking under 2 hours.
As a bonus you often get some free meter seals if you ask nicely!
It gets very expensive if you ask them to do the excavations, but if you get it all ready for them it's fairly reasonable.

I'm wondering if the client could end up with an 100 amp TNCS supply at the house for similar money to the cost of the SWA, associated switch gear, and your labour charges for wrestling with it all.

 

[brianmoooore]

I'm wondering if the client could end up with an 100 amp TNCS supply at the house for similar money to the cost of the SWA, associated switch gear, and your labour charges for wrestling with it all.

There's also the losses in that 50m sub main to be paid for. Small amounts, but they build up over the years, especially if there are heavy loads for long periods, such as heat pumps or EV charging.

 

[bennie]

If your using 35mm or 50mm use 2 core SWA and use the armour as the earth, it'll cut down on price. I know people will comment on this but the armour us fine to use and CSA fir the copper equivalent is fine.