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Topic Title: SWA
Topic Summary: Rating
Created On: 12 August 2014 09:40 PM
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 12 August 2014 09:40 PM
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Ampman

Posts: 1041
Joined: 06 February 2006

Evening ,

I want to run a sub-main around external to a house & need to use swa i was thinking of using 10mm swa as its rated at 67 amps & protect it by a 50 amp breaker ,

In the kitchen there will be 12 amps underfloor heating , dishwasher , fridge frezzer , led spot lights . led plinth lights , led under cabinet lights & a 6kw oven ,

I want to use 10mm as its easier to clip etc ...

16mm swa is a pain to use .

Length of run is 20 mts ,

Just worried that 50 amps might trip if everthing on at once ,

Or would you put 10mm swa on a 63 amp mcb ?

Advise please cheers
 12 August 2014 10:40 PM
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AJJewsbury

Posts: 11768
Joined: 13 August 2003

I wouldn't be too worried.

Have a look at the kitchen load in this wiring matters: http://electrical.theiet.org/w...circuits.cfm?type=pdf

Presumably the 6kW is a complete cooker rather than just an oven - so a fair bit of diversity with various hotplates, simmer stats and so on (or new fangled equivalents) - so < 15A for that.

I'd probably go for a HBC fuse rather than an MCB to supply the submain - just to have some discrimination. Probably would go for 63A for the same reason.

- Andy.
 12 August 2014 10:49 PM
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industryspark

Posts: 560
Joined: 23 October 2006

Well i haven't got my BGB on me but if you are saying that the 10mm is good for 67A with the installation method then you might aswell utilize that and use a 63A CPD. Just be carefull that your using the PVC swa ratings and not the XLPE ones, im sure you know that though and like i said, my regs are at work.

Looking at the loading you describe, i cant see as you will have any problem what so ever regarding getting it near to tripping for an overload. We tend to overestimate how much power we are going to drag when the reality is that its hardly ever as much as you think it will be, i have been guilty of this myself at times, certainly when i started out.

Regards
 13 August 2014 09:08 PM
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hertzal123

Posts: 330
Joined: 26 August 2007

As far as I know,all swa is normally not pvc these days and without looking in the book the mcb would be 50A for 10mm.
Regards,Hz.
 13 August 2014 09:42 PM
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leckie

Posts: 2021
Joined: 21 November 2008

That's what I thought, that all swa nowadays is XLPE?
 13 August 2014 11:00 PM
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peteTLM

Posts: 3233
Joined: 31 March 2005

I think the point industryspark is making is that you are running the cable to 70' C as for PVC and not 90' for XLPE, and so using the PVC table.

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 13 August 2014 11:08 PM
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industryspark

Posts: 560
Joined: 23 October 2006

Indeed Pete. I cant remember when i last recieved some pvc swa from the wholesalers as its nearly all xlpe now. However, we have to use the pvc table ratings for the xlpe stuff unless we can confirm any equipment a cable connects to is rated for operation above 70' degree c.
 13 August 2014 11:16 PM
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peteTLM

Posts: 3233
Joined: 31 March 2005

Indeed.

Im sure its all a conspiracy, certainly around these parts. No 2 core SWA at all, and all XLPE even when not required.

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----------------------------------------
Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 14 August 2014 10:02 AM
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AJJewsbury

Posts: 11768
Joined: 13 August 2003

and all XLPE even when not required

I suspect there's a gradual move from PVC to XPLE - most BS 8436 cables seems to be XLPE too. I believe that XPLE contains fewer 'nasties' than PVC (chlorine?) - which gives advantages in manufacturer, fire performance and eventual disposal.

- Andy.
IET » Wiring and the regulations » SWA

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