What is the correct way to calculate cable size?

[Gigagator]

This is merely out of curiosity, as I am keen to learn more about electricals.

What is the correct way to calculate cable sizes for mains circuits? Start easy please if you would with a simple scenario such as installing a lighting circuit in a loft, cables clipped to timbers for a 36w tube, for example.

What calculations would one make?

Note this is not something I plan on undertaking, just want to learn. Thanks.

 

[riveralt]

http://www.tlc-direct.co.uk/Book/4.3.9.htm

 

[Gigagator]

http://www.tlc-direct.co.uk/Book/4.3.9.htm

Thanks for the link! Favourited. Back to work now though, damn night shifts

 

[mikhailfaradayski]

lol, hello again Gig,

I'm starting to get the feeling that the 'full rewire in 2013 when the kitchen is re-fitted' isn't really going to happen is it?

It seems as though you missed an opportunity to ask your question to the spark who you should have called some weeks ago to rectify your dangerous electrical installation. -but you didn't call a spark in did you?

Does your installation still look like it does in the photos in this thread? -

//www.diynot.com/forums/electrics/strange-little-situation-any-thoughts.311323/

 

[Gigagator]

Does your installation still look like it does in the photos in this thread? -

//www.diynot.com/forums/electrics/strange-little-situation-any-thoughts.311323/[/QUOTE]

Yes it does, Mikhail. You seem to forget I am not the homeowner, that title rests with my parents. I've passed my thoughts and feelings onto them and the opinions of the competent and the qualified (i.e. You guys in this forum) and it has been duly noted.

But sadly I cannot make them do the work and they've made the decision to get everything done in 2013 along with a new kitchen. Yes, the full rewire in 2013 is going to happen. They're adamant on getting a new kitchen and finances will be available then, and they have no choice but to get a full rewire because they are aware of the state of the electrics.

But anyway, the only reason I asked that question about calculations was because I was curious how a qualified electrician calculates the correct cable size.

I read the forum daily and I'm forever reading posts where someone says 'Have you done your calculations for cable size?' for example, but I've never understood how the calculations work myself, so wanted to find out.

I wouldn't attempt to add circuits to the house as it is, largely based on the information you guys gave me on the state of my house in my previous thread, and also because I know I'm not competent enough at this current stage to be messing with dangerous electrics.

 

[mikhailfaradayski]

If, as you say, wish to pursue a career in electricals, it really wouldn't hurt tyo buy a copy of the regs and read it. All the information you need is contained within.

As the regs changed at the beginning of the year, you might be able to go to fleabay/amazon or similar to find the previous version at a budget price.

Although outdated, the information about cable sizing/fuse ratings/disconnection times/volt drop/ will still be relevant.