circuit design

[davidcaulfield]

Hi guys I have always been told by my boss which cable size to install. He doesn't work out why size cable to use.

I went to a job yesterday and it was a garage board being fed by a 2.5 T&E off a socket.

The garage is being made into a little office with 4 double sockets and 2 convector heaters and a kettle.

I recommended a 6mm T&E through the roof of the bungalow an throughout the metal conduit going to garage over head.

Does every1 calculate which cable size should be installed or do they use a rule of thumb so to speak.

Appreciate any help with this

 

[Engineer54]

To determine the size of cable to be used, without calculation comes only from long experience, taking into consideration what length, installation method, and load that cable is likely to carry.


It's easy to just say i'll install a 6mm cable as a cover all for arguments sake, but doing this type of assessment, will in some cases, cost you very dearly!! ...lol!!

 

[ackbarthestar]

Does every1 calculate which cable size should be installed or do they use a rule of thumb so to speak.

It would be wise to particularly as it is a sub-main. Other factors will include not just maximum demand and diversity but also volt drop, future additions, fault protection in its various disguises....

 

[GLENNSPARK]

6mm will be OK...i hazard..lol..
how long is the length of run?

whats the earthing arrangements and are we talking an armoured sub....or twin or summat?

 

[Guest55]

6mm will be OK...i hazard..lol..
how long is the length of run?

4 miles :-D

 

[ackbarthestar]

4 miles :-D

Lol...... This garage must be installed at the end of his private airport. Will need a 11kV TX link then ?

But that's ridiculous no garage can be installed that far away from a private supply. Better contact the DNO to put in a 23kVA service head.......

We could go on but E54 has given sound advice.
Remember if you signing this installation off then do your homework.....

 

[Guest55]

Lol...... This garage must be installed at the end of his private airport. Will need a 11kV TX link then ?

But that's ridiculous no garage can be installed that far away from a private supply. Better contact the DNO to put in a 23kVA service head.......

We could go on but E54 has given sound advice.
Remember if you signing this installation off then do your homework.....

23kva ??? you think too small , i'd go for the uranuim fuel cell in the greenhouse -
half life of 27 years , volt drop not a problem

 

[GLENNSPARK]

just park this thing up and run it all off that....

 

[shanky887614]

just park this thing up and run it all off that....

View attachment 19881

worse case you can go and see biff in his prime :biggrin5:

 

[Guest55]

cheeky monkey , i'm a young & trendy 41 year old ;-)

 

[davidcaulfield]

Ok how would you calculate a 25meter run through a loft. The demand is 2 pendants and 2 heaters and a kettle. Tncs system

 

[ackbarthestar]

Ok how would you calculate a 25meter run through a loft. The demand is 2 pendants and 2 heaters and a kettle. Tncs system

There were a whole load of very good sticky posts explaining the basics of cable selection. I can't seem to find them, but then I haven't really looked.

Three things to consider
1/ the method of earthing and any corresponding fault currents
2/ sub main circuit design
3/ Final circuit design