R1 + R2 of two core SWA

[R32]

This is what I have so far, load = 42A cable chosen - 6mm = R1. R2 is the copper equivalent csa which = 9.75mm[SUP]2[/SUP]

The closest to this I found is -10mm[SUP]2[/SUP] line conductor and 6mm[SUP]2 [/SUP]protective conductor

Getting to the point I think I can just reverse this to get R1+R2 so 6mm line and 10mm cpc ?

Last and least finding ambient temp correction factor for 35 degrees I found either 0.94 or 0.97 for 70[SUP]o[/SUP] and 90[SUP]o[/SUP]​ resp.

 

[malcolmsanford]

a 6mm SWA will have for

70c equiv 24mm where 13mm is only required

90c equive is 22mm where 18.5 mm is required

What are you trying to achieve?

 

[R32]

It's just a academic exercise, I want to find R1+R2 of a SWA cable able to carry 42A but I have never done SWA cable before

 

[malcolmsanford]

If I can help I can.

If your doing this as you say as an academic exercise you will have to start going into the SWA resistivity which is about 8:1 of copper, but normally you will need to have the manufacturers technical specs, Eland are good and you can get them easily of the web. You then have to calculate the same way you would R1 or R2 and that is

mΩ/m x Length/1000 that will give you at 20c, and you then put in any of your CCC co-efficient

In the real world of design you use, tables that are published all over the net and easily got off, that give you the equivalent that I posted earlier. These tables are guides and sometimes they may show that a SWA is not sufficient. We can then use the formula CSA = K2/K1 x SWA section

Where K1 is the phase conductor ‘K’ value from BS7671 table 43.1

And K2 is the protective conductor (SWA) ‘K’ value from BS7671 table 54.4

If you have it have a read of GN 1 it is good for SWA and using it as the CPC

 

[R32]

I only have the on site guide at the moment. How would you go about picking a SWA cable for 42A? I cannot find a table anywhere... only non armoured in my on site guide. It is really getting the better of me as I have flu and can't think straight

 

[Engineer54]

Before we start going round in circles, where are you getting this 42A from, in other words what is this 42A load derived from??

 

[R32]

OK fair point the question is, A 2 core SWA cable at 10m in length is to support a load of not less than 42A. Select a suitable cable and determine R1+R2 at 35[SUP]o[/SUP]C

 

[Engineer54]

Ahhhh!! just a course question then... In that case what Malcolm has posted is all you need to calculate your answer... I'd say a 4mm SWA XLPE cable with a 49A (ref 1) current rating is a good starting point for you. 6mm will have a 62A rating with the same reference method...

 

[R32]

Ah brilliant thank you so much. I think the resistance of 4mm XLPE 7.9 mOhms per meter for R1. Then R2 (the steel armour) would have an 8:1 ratio with copper?

 

[R32]

I found this
http://www.batt.co.uk/upload/files/xlpeswalszhbs6724_1227548172.pdf

Second table shows the for 4mm XLPE 58% the conductivity of R1

Am I reading this correctly??