whizBan-all_sheds (and any one else!)- all that stuff applies to a circuit that in theory draws 6a maximum. How would you calculate exactly what current the circuit will draw under normal operating circumstances? Going from my example,of 2 rooms with 3 down lighters,shaver point, exctractor how would you calculate the current drawn? As i mentioned in the earlier emails, is an alternative to sum up the power ratings of individual items in the circuit and see if it fall below the given set rating? Please forgive me if appear naive - thats simply because i am!
Basically, if this was a job of yours how would you go about assessing it and determining what you need ?
Well - I'm happy to tell you what I'd do, but I must point out that I'm not a qualified electrician. Neither am I clueless, but if I say anything here that's wrong, I trust that one of the pros will correct me - that way we both learn.
As breezer says, in practice you mostly wouldn't bother, for a "normal domestic" installation, as it just isn't worth anyones time, and therefore money, to decide if 1.0 or 1.5mm cable is needed for the lights. If it's a very big house, and you've got either lots of big rooms, or very long runs from the CU, you might find you need 2.5mm. But not often, and I guess one of the things that comes with experience is being able to make those determinations without a lot of detailed work. Which means that you
should know how to do the calculations,
and actually do them at first until you are confident that you can simply look at a site, make a few quick estimations and come up with an answer which you know will meet the requirements of the customer
and in a way that conforms to BS7671.
In this case the right thing to do would be just to add everything up, as it would be quite reasonable for everthing to be on at once. And then have a look around and think what might be added in the future, e.g. might someobody want to replace the light in the bedroom with one that has 3 or 4 100w lamps in it? Would wall lights here and here be a possibility? Might someone drill through the wall to feed floodlights outside? Everywhere you go, start looking to see what people tend to do so that you can allow for future expansion.
But as for other circuits, there are all sorts of guidelines and accepted practices for estimating the maximum demand, and there you're into something called diversity, where, basically, you don't assume that because a ring main has 10 2-gang sockets on it that the maximum load is going to be 260A!
You can read about all that here:
http://www.tlc-direct.co.uk/Book/6.2.1.htm (I can recommend buying that book, BTW).
Here's another example, in this case the factors to consider in kitchens:
http://www.iee.org/Publish/WireRegs/Amd1andRC.pdf
Also I'm sure that the On Site Guide and various IEE Guidance Notes will have information on this, and if you're studying for your C&G at college then I expect the topic will be introduced at the appropriate time.
scobyIs this the same for other cables ? can you enlighten me on all up to, say, 10mm ?
It's the sort of trivial info I love to collect. I've tried the k-zone you mentioned but I can't get into the tables
Yo - some of the #placemark links on the k-zone site don't work (well, he does work for Sun....
) - scroll down until you find the tables. Also, if you're going to use info like that (i.e. just put on a website by some private individual, whom you don't know from Adam, and who, for all you know, might be a complete idiot
), you should satisfy yourself that he's got it right. You can find info on cable calcs here:
http://www.tlc-direct.co.uk/Book/4.3.1.htm.
I keep plugging that book/website - I suppose I should say something like "other reference books are available", (even though I don't know what they are).
