How to work out the total design load to find my swa cable size

[Ted Curly]

Hi all I am having trouble trying to work out the total load and swa cable size.
I have 10 circuits in a outhouse 40 meters from the mains power supply 1 x lighting with 10 lights, 1 x lighting with 10 lights.
1 x 2.5mm radial for 2 heaters, 1 x 2.5mm radial for heater. 3 x 2.5mm socket rings with 3 sockets on each ring, 1 x water heater radial for 2 instantaneous hot water... I have calculated the lights at 100w per light x 20= 2kw, the heaters are around 3kw x3 =9kw.
Water heaters 3kw each=6kw... The problem is the sockets as I'm not sure what's going to be plugged in apart from a kettle. working them out at 13amp x 230v gives me nearly 3kw per socket x9 = 27kw which seems unrealistic... Adding all that up before diversity is 44kw which seems way ott for that. Thanks all

 

[Ted Curly]

I think you need to contact your DNO to arrange a new 100A supply.

Hi the main, supply is 100a in the house this is to power an outbuilding

 

[Deleted account]

What is the total load after diversity in the house at present?

The reason I ask is if it’s 80amps then you only have 20 amps left for the outbuilding. Will this be enough?

 

[Baddegg]

Hi the main, supply is 100a in the house this is to power an outbuilding

He knows that ted he’s saying that if the upfront fuse is 100a and is already serving the house you’d need to deduct that usage (after diversity before you could think about using it on the outbuilding as well,
Diversity is more than just the 40% rule have a good think about how realistically the circuits will be loaded, for instance when you say 20 lights over 2 circuits you are unlikely to get near 100w total over both circuits with leds let alone 100w for one light

 

[MJPD29]

Although 96 amps sounds like an awful lot for what your talking about, presuming the swa is buried in a duct or ground or whatever I can't work out how you got 16mm

 

[Ted Curly]

What is the total load after diversity in the house at present?

The reason I ask is if it’s 80amps then you only have 20 amps left for the outbuilding. Will this be enough?

Will check the house 2mo as I not to sure, I have wired bigger extensions with a load more fittings and never had a problem before, just put of as this is a 40meter run my gaffer told me to use 10mm swa but as I know this is wrong and have my own 18th edition I am liable if it hits the fan so I want to be exact sure of everything to the tee my nick name used to be health and safe ted. 96amp ib seems a lot for 20 led spots, 9sockets, 3 heaters and to water heaters instantaneous. That is like 22kw

 

[Deleted account]

Didn’t realise you where working on someone else’s house. I thought you where working on your own property.

Is your boss an electrician?

Does he know about loading and cable calcs.

You quite rightly point out it’s your liability if your the qualified supervisor, not his.
If the property does not have a big enough supply, tell him and the customer.

Your profile is limited so I don’t know the extent of your experience or qualifications.

 

[Ted Curly]

Although 96 amps sounds like an awful lot for what your talking about, presuming the swa is buried in a duct or ground or whatever I can't work out how you got 16mm

The 16mm swa is clipped direct 3core, 94amps current carrying capacity is what I found out from the technical information from the wholesaler when contacted them, as I couldn't find it in the books and online was getting different amounts. In your knowledge what would you say the current carrying capacity of 16mm swa 3core clipped direct and buried is.

 

[MJPD29]

The 16mm swa is clipped direct 3core, 94amps current carrying capacity is what I found out from the technical information from the wholesaler when contacted them, as I couldn't find it in the books and online was getting different amounts. In your knowledge what would you say the current carrying capacity of 16mm swa 3core clipped direct and buried is.

Clipped direct is fine I was only taking a guess at buried

 

[Ted Curly]

Didn’t realise you where working on someone else’s house. I thought you where working on your own property.

Is your boss an electrician?

Does he know about loading and cable calcs.

You quite rightly point out it’s your liability if your the qualified supervisor, not his.
If the property does not have a big enough supply, tell him and the customer.

Your profile is limited so I don’t know the extent of your experience or qualifications.

Hi yes it is my uncles house I started out on my own in November after 15years with the council doing house bashing and so on electrically for them and have just ended up subbing out to a company with 6 of us since then and get left to it completely,
I have 15 years experience in wiring and have my level 2-3 +my 18 edition and my testing and inspection +part p and a hnc in construction, I know my job just not may council houses required lavish outhouses to be fitted by us requiring 40meter runs of swa, I am new to forums and appreciate all the views from follow sparks and the vast knowledge you bring from each sector of r trade thanks guys.

 

[Deleted account]

Haven’t got my book to hand but it’s not 94amps

Minimum 25mm would be required if it’s 94amps, however if it is 94 amps then you’ve got 6 amps left for the main house.

Is that enough?

At a guess 16 mm SWA is about 70-75 amps( guess).

If buried this will drop to maybe 63-68 amps( again a guess).

It’s all in the big blue book. You should be able to get these figures for yourself and work it out.

Do not use my figures, they may be wrong.

Don’t forget to do voltage drop on cable size and pfc.

 

[Deleted account]

Is this your personal job and the gaffer you normally work for recommended you use 10 mm SWA? Or is this not your job and your working for a gaffer?

Is the gaffer an electrician?

 

[Charlie_]

“Is the gaffer an electrician?”

No I think he was the boss of a small engineering company in Yorkshire

 

[Charlie_]

 

[Spoon]

Selwyn Froggitt...

 

[Charlie_]

Selwyn Froggitt was the program he done before the gaffer.. Fred was his name in the gaffer