Cable Calcs

[Steve D]

Hi All,

I'm rewiring a garage. There is SWA into the garage and I intend to fit a new RCD protected garage CU with 16A & 6A breakers.
Would you recommend putting a 25A or 32A breaker in the main CU ?

I haven't inspected site properly yet but I just had a thought with respect to the existing SWA cable sizing which is currently buried. Am I right to assume that the cable needs to be sized in accordance with the size of the CU fuse? Therefore a 32A breaker at the CU demands that the cable is capable of carrying minimum 32A ?

Excuse my ignorance but I'm never really worked with SWA in the real world before, so what is the difference between tables 4D4A 70C armoured thermoplastic and 4E4A 90C armoured thermosetting? I've got a note in my regs to generally use table 4E4A but naively, I don't really know have to identify what type of SWA exists.
Will there be some sort of code on the external of the cable for me to identify ?

Cheers
Steve

 

[Guest123]

2.5mm protected by a 32A breaker, really???

Yes

Well depending on number of cores and installation method this exceeds the CCC of the cable.

It might just be me but I wouldn't entertain the idea of protecting a 2.5mm with a 32A MCB regardless of what the book says it can handle, it just doesn't sit right. 20A MCB max.

 

[BristolSpark]

I thought 2.5mm cable was only capable of taking around 27amp max in the best of conditions. 20amp would be better suited for 2.5mm radial. surely!!!!!

4mm cable will run on 32amp fine I believe at a push a 40amp mcb

 

[Guest123]

Hey bud.

We're talking SWA which according to the book will carry in excess of 38 odd amps in ideal conditions, i.e a 2 core on perforated tray in free air.

Other than that the max is bewtween 31 and 33A which means it would be operating at maximum capacity under a 32A MCB which is not advisable. Also by the time derating factors are taken into account there is a chance the cable would begin to overheat before the protective device would operate and we all know what that means.......

 

[scotsparky]

BBQ? I will bring marshmallows!

 

[Mr Mark Sparks]

bbq
i have just had 1st bbq this year
i like a nice juicy sausage

 

[scotsparky]

bbq
i have just had 1st bbq this year
i like a nice juicy sausage

Mark can you rephrase that just to clarify how you like your SAUSAGE?

 

[grandad]

Well depending on number of cores and installation method this exceeds the CCC of the cable.

It might just be me but I wouldn't entertain the idea of protecting a 2.5mm with a 32A MCB regardless of what the book says it can handle, it just doesn't sit right. 20A MCB max.

agree with that..2.5mm=20A, 4mm=32A.
I always wire garages in 6mm on a 32A ...extravagent or what?

talking of banjos (the forbidden word) has anybody else used these, i think they are fantabulous.
i dont get them from tlc but gives you an idea
Piranhna Earth Nuts - Pirahna

 

[Spudnik]

Must admit i always do 32A on 6mm.

Strange really considering 6mm is not really suitable for 40A MCB if the load is ever beefed up, so why dont we just use 4mm?

 

[grandad]

Must admit i always do 32A on 6mm.

Strange really considering 6mm is not really suitable for 40A MCB if the load is ever beefed up, so why dont we just use 4mm?

always better to have a bit more...dont forget to look at my shiney nuts

 

[kung]

talking of banjos (the forbidden word)

What do you call Banjos then yer look toms playing his frying pan again ! not to mention the battle of the (frying pans)


has anybody else used these, i think they are fantabulous.
i dont get them from tlc but gives you an idea
Piranhna Earth Nuts - Pirahna
View attachment 262[/quote]

Yer saw these at my local suppliers think i will have a go on these ! Piranha

 

[Spudnik]

talking of banjos (the forbidden word)

What do you call Banjos then...

earth tags...

 

[Guest123]

Or...

A stringed instrument comprising 4 strings designed to be played by holding in two hands one to alter note pitch and one to pluck the afformentioned strings in order to produce the desired note.

If you want to be P.C!!!!!

 

[andyb]

talking of banjos (the forbidden word)

What do you call Banjos

Banjos?

 

[scotsparky]

Or...

A stringed instrument comprising 4 strings designed to be played by holding in two hands one to alter note pitch and one to pluck the afformentioned strings in order to produce the desired note.

If you want to be P.C!!!!!

Isnt that a Ukulele like the one George Formby played?

" Leaning on the lampost on the bottom of the street "
"For a certain little lady to walk by"
" O me o my"


all together now!!!!!!!!!!!!

YouTube - Leaning on a Lampost - George Formby

 

[Guest123]

Isnt that a Ukulele like the one George Formby played?

Same horse.