Garage fed by 4mm SWA

[1shortcircuit]

I'm not trying to fall out with either of you guys. I often look for your posts and can admit that I have learnt a lot from them.

On this occasion I believed the posts to be harsh but it seems yesterday I must have engaged my brain incorrectly as this is not the only thread where I read posts in a way that they were not meant.

I think I'll go and clean my ears out so I can hear the tone of the posts correctly next time:bigear:

:38:

 

[BigJonesy]

I'm glad this question has been asked as I also want to know how this works. I'm new to the industry and am just training but don't know how to work out what would be safe. If an extension was fed by a 32 amp breaker, and is running a couple of light circuits both at 6 amps I think that would be fine. But if you wanted to add sockets at 20 amps would that be OK as it adds up to 32 amps? Please don't jump on me, I just want to ask that's all. Also, where would I find out how to work this out? Someone said times it all by 0.4 and that will give you the figure. For 32 amps on the circuit that would give me 12.8 amps wouldn't it? It's like a jigsaw to me all of this, bits and pieces of knowledge from all of the place, I just need to slot it all together. Thanks all.

 

[tuckermot]

Hi bigjonesy
all the information you require for your question is in the on site guide .There is a table in there that gives you diversity for all the circuits .Example if you put in two 13 amp sockets it does not mean you have to allow 26 amps on that circuit thats where diversity comes in it is a average usage likely to be used on that circuit

Richard

 

[BigJonesy]

Hi bigjonesy
all the information you require for your question is in the on site guide .There is a table in there that gives you diversity for all the circuits .Example if you put in two 13 amp sockets it does not mean you have to allow 26 amps on that circuit thats where diversity comes in it is a average usage likely to be used on that circuit

Richard

Brilliant, cheers tuckermot. At the risk of being a cheeky ****er do you know which pages in the OSG will tell me this? I've got the red one, not the new green one. Top man if you can help like.

 

[tuckermot]

i have sold my own red one but itis in there under diversity in the index bud

 

[BigJonesy]

i have sold my own red one but itis in there under diversity in the index bud

You're a star mate, I'll have a look through mine now. Just to get down to proper basics, if the amps are less than the MCB it's on - say it's a 32 amp MCB and it's running 26 amps in the extension, would that be OK? I just don't know where the cable size fits in. I know I'm being a thick tw*t but I just don't know hahahaha.

 

[tuckermot]

just remember the breaker ( mcb is to protect the cable from over current damage ) so the mcb should allways be a lower rating than of the cable thats why 1.5mm twin and earth is rated at 16-17 amps and the mcb is rated at 6amps but it is quite accepatable to put in a 10amp mcb with this cable if you are adding more lights or at design stage if you know the current is going to greater than 6 amps by doing your ohms law power divided by volts =amps so if you have 10 lamps rated at 60 watts each so 600w divided by 230v =2.6amps so you are safe to install 1.5mm cable and a breaker ,mcb rated at 6amps hence the cable can carry 16amps you are going to draw 2.6 amps max with out diversity so 6amp mcb is fine hope that helps using simple ohm laws in different ways to get your answer

 

[Spoon]

Just to add to Tuckers notes, if you look in the BGB at pages 317 onwards it shows you the different installation methods of cables. This will also affect your calcs for the cable size.