Discuss How to work out the total design load to find my swa cable size in the Electrical Forum area at ElectriciansForums.net

Paignton pete

Regular EF Member
Messages
779
Location
Over the rainbow
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.
 
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Ted Curly

EF Member
Messages
24
Location
Birmingham
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.
 

Matthewd29

Regular EF Member
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1,192
Location
Belfast
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
 
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Ted Curly

EF Member
Messages
24
Location
Birmingham
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.
 

Paignton pete

Regular EF Member
Messages
779
Location
Over the rainbow
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.
 
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Paignton pete

Regular EF Member
Messages
779
Location
Over the rainbow
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?
 
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Ted Curly

EF Member
Messages
24
Location
Birmingham
Yes the gaffer is also a spark with 20 years in the job, my gaffer not interested in this project as its me uncles place for me auntie and there is no money involved, I just don't want to look a numbty if I get the swa cable size wrong and it's expensive and dangerous I will have to calculate again to get the ib down, like you say I will no where near be using 100w per light with leds in place
 

Pete999

Forum Mentor
Messages
21,810
Location
Northampton
I have worked out the total ib of the circuit at 169.88amps and with added diversity came up with 120.36amp,,,, but if I do the 3 sockets rings as 20amp radials diversity will come in at 96.36amp..
How did you apply the diversity?
 

Pete999

Forum Mentor
Messages
21,810
Location
Northampton
Hi I was just following the OSG Table A2 for diversity on the circuits, the sockets as I don't know what is going to be plugged in I used the breaker rating(what other option without knowing) , the lights I have assumed 100w max per fitting I know this is now old and we all use leds, the swa mains to supply the circuits will have to be min 16mm as 40 meter run, I am right to think thst the iz of the 16mm swa 3core is 94amp clipped direct, thst will be a problem if my ib is 96amp,, I need to re work the figures to find realistic figures for lighting and sockets as they won't be drawing that much Im being to cautious as I have to present my figures to my gaffer and Building control Friday. Thanks again all
This Gaffer you speak of, is he delegating the design of this project to you as an exercise to test your metal, or does he not know how to do it himself?
If it's the later then he should employ a designer to scope out the design, nothing wrong with getting you to attempt the design and correct your work if it's required, but the way it sounds us he is using you as a scapegoat, should the design element go Boobs up.
 

Spoon

Forum Mentor
Messages
7,166
Location
Lancashire
Selwyn Froggitt was the program he done before the gaffer.. Fred was his name in the gaffer
Yes mate. Thats how I always remember the bloke, from Selwyn Froggitt. I should have been more informative.. :laughing:
 

Paignton pete

Regular EF Member
Messages
779
Location
Over the rainbow
Yes the gaffer is also a spark with 20 years in the job, my gaffer not interested in this project as its me uncles place for me auntie and there is no money involved, I just don't want to look a numbty if I get the swa cable size wrong and it's expensive and dangerous I will have to calculate again to get the ib down, like you say I will no where near be using 100w per light with leds in place
That makes sense.

Good luck on the calcs.

Can you come back to us again once you’ve done it.
 

westward10

In echoed steps I walk across an empty dream.
Staff member
Moderator
Messages
11,539
Location
Northamptonshire
Allowing for 63A over 40m and a 2% volt drop, this allows an extra 1% for your lighting to comply with a 3% requirement you will need a minimum 25mm cable.
 
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Ted Curly

EF Member
Messages
24
Location
Birmingham
How did you apply the diversity?
Hi I did diversity for the sockets 100% first circuit 50% of other two, I used the 20amp breaker rating as I gonna have to find out what is plugged in (unless there a better way) , the lights I worked out for 100w max a fitting I know thst well ott il have look at fitting and use bulb rating spose, then 66% for each light circuit diversity so did 10lights 100w per fitting = 1000/ 230 =4.34amp for each circuit I have two, the heaters (39.12 @ 3000/230 x3 )I took the first 10a of 1st then 50%remaininf two left me with 24.56a @ 3000/230 and the water instantaneous heater no allowance. Total diversity 96.36 way to high if calcs was more accurate regarding light bulb w and socket load would be lower
 
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Pete999

Forum Mentor
Messages
21,810
Location
Northampton
Hi I did diversity for the sockets 100% first circuit 50% of other two, I used the 20amp breaker rating as I gonna have to find out what is plugged in (unless there a better way) , the lights I worked out for 100w max a fitting I know thst well ott il have look at fitting and use bulb rating spose, then 66% for each light circuit diversity so did 10lights 100w per fitting = 1000/ 230 =4.34amp for each circuit I have two, the heating I took the first 10% of 1st then 50%remaininf two left me with 24.56a and the water instantaneous heater no allowance
Thanks
 

davesparks

Forum Mentor
Messages
12,803
Location
guildford
Hi apologies, I just assumed discrimination if it was in the main existing board, the sub board would not need RCD, the tt I was just learnt many years ago if the out building was some distance from the house to install tt as there is no extraneous parts made from wood and plastic so no need for pme, sorry guys if to old skool. I do think it is best to use the existing TNCS.

What is the reason you were given for converting to TT if its over a certain distance? And for that matter what value do you use for the distance at which you need to do this?
What do you mean by no extraneous parts therefore no need for PME?
None of this sounds 'old school' to me, more like nonsense!
 
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Lucien Nunes

Respected Member
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2,822
Location
London / Tallinn
The process seems to have started in the wrong place, with a list of final circuits. It should go something like this:
1. What equipment is going to be used in the new building?
2. What is its total load?
3. What is the total load of the house?
4. Is the supply large enough for both?
5. If so, what cable is needed to feed the new building.
Then you can get to the details of RFCs or radials etc.

The fallacy at the moment is that you've chosen some final circuits without knowing the load, then tried to assess the load from the choice of circuits.
 
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Ted Curly

EF Member
Messages
24
Location
Birmingham
What is the reason you were given for converting to TT if its over a certain distance? And for that matter what value do you use for the distance at which you need to do this?
What do you mean by no extraneous parts therefore no need for PME?
None of this sounds 'old school' to me, more like nonsense!
Hi it was just the way was taught many moons ago regarding tt and outbuildings ,,, and the no extraneous parts was meant to indicate for this instance the out building is made of wood no metal, and if used tt would be no pme, but dnt worry about tt I going to use the tncs earth, sorry about the way I type not very good at typing on these small phones and new to forums cheers guys.. Also I will have update on what equipment is going to be used tomorrow so can make better assumption of ib of sockets,, sorry so late to reply had 12 hour day and at it again in 8
 
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Ted Curly

EF Member
Messages
24
Location
Birmingham
Allowing for 63A over 40m and a 2% volt drop, this allows an extra 1% for your lighting to comply with a 3% requirement you will need a minimum 25mm cable.
I was hoping it wouldn't come to thst size the 40m swa will be clipped direct ,the lighting circuits max length run will be around 10meters,, 16mm swa Vd is around 2.6 mV/a/m
 
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Ted Curly

EF Member
Messages
24
Location
Birmingham
I was hoping it wouldn't come to thst size the 40meters run of swa will be clipped direct ,the lighting circuits max length run will be around 10meters,, 16mm swa Vd is around 2.6 mV/a/m
 

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