# Cable Sizes & Breakers



## HelloBuddy7 (Sep 21, 2012)

Minimum size cable **


Thanks


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## butcher733 (Aug 4, 2012)

Many variables. What is the application?


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## chewy (May 9, 2010)

butcher733 said:


> Many variables. What is the application?


Cheating on an exam.


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## HelloBuddy7 (Sep 21, 2012)

chewy said:


> Cheating on an exam.


Good One.

And Butcher.. Does it not work like a 32A breaker has to be 4mm minimum unless its a ring? 

If you understand that?

Cheers


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## butcher733 (Aug 4, 2012)

I would wait for someone familiar with European installations to chime in. I'm out of league on this.


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## 480sparky (Sep 20, 2007)

Moved to the UK section......... OP will more likely get more responses here.


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## wildleg (Apr 12, 2009)

responses


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## WarrenG (Apr 25, 2012)

When you say minimum size for breakers, its a rule of thumb that the cable is rated higher than the protecive device otherwise the cable will burn / catch fire before the protective device gets to operate. 

There will be a number of pages within the OSG and the Regs book outlinng different methods of installation and the cable size ratings. Take a look at these _(sorry haven't got mine to hand but I think its something link App 6 OSG)_ and they will determine what size of protective device you will require for your designed current

Something simiar to this:

http://www.doncastercables.com/technical/datasheets/multi_core

For example (_and occording to the above chart_) a 1.5mm cable clipped directly to a wall (_Ref Method 1_) will be rated higher (_17.5A_) than a 1.5mm cable being run under thermal insulation (_13A_).

This is basic because there are a few other factors to consider in design, such as ambient tempertures, Correction factors, grouping factors, voltage drop etc but here is quick guide to remember for rule of thumb.


Calculate the design current - Ib _ (* required, usage, start-ups, diversity etc)_
Select the rating of a protective device - In _ (* higher that the required design current)_
Choose the correct rating and size of cable - _(* needs to be rated higher than the protective device)_
Its always good practice to consider future expansion for certain circuits, i.e. Showers are always advancing in terms of kW. Install cables where it will do the job you want it to do currently, but could also be used if the customers wanted to upgrade their systems.


Hope this helps.


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