Swa/pvc cable size

[Deleted member 26818]

Here's one way:
Electrical Conductivity of Materials - Resources - Blue Sea Systems
Although it's not very exact as the conductance of steel is indicted as being between 3 to 15. With copper as usual being 100.
I use the 8:1 ratio.
Yes, John Peckham he's the chap.
Of course this is all a bit rule of thumb.
The only way to really determine the equivalance would be to physically measure the actual materials being compared.

 

[Engineer54]

Spin,

Well, for the best part of my years i ''Always'' used to go by calculation, but now basically use this guy's table as a good rule of thumb. When cable lengths start getting long, i will still calculate, just to be on the safe side, especially where compliance is just scraping through.

 

[Deleted member 26818]

Same here.

 

[Chr!s]

I use the 8:1 ratio.
Yes, John Peckham he's the chap.
Of course this is all a bit rule of thumb.
The only way to really determine the equivalance would be to physically measure the actual materials being compared.

Spin, you only want to use this where bonding applies though

 

[Deleted member 26818]

Spin, you only want to use this where bonding applies though

CPC and bonding, except where PME conditions apply.

 

[Chr!s]

CPC and bonding, except where PME conditions apply

Not for a cpc spin

 

[Deleted member 26818]

Not for a cpc spin

That's what I use the table for.

 

[Engineer54]

That's what I use the table for.

Same here!! In fact that is what the table is identifying ''Minimal CSA of SWA armouring to meet requirements of cables CPC''

 

[Chr!s]

Same here!! In fact that is what the table is identifying ''Minimal CSA of SWA armouring to meet requirements of cables CPC''

Not saying theres anything wrong with tables, just saying you dont use the 8 - 1 ratio

 

[Deleted member 26818]

The chart indicates which cables have armour that would comply with Table 54.7 in BS7671 (Table 54G in my chart). The sizes in brackets are those that don't comply with Table 54.7, and would need to be checked using the adiabatic equation.
I believe John has updated his Chart for the 17th, although I haven't bothered asking him for the updated version, as it has essentially the same information as the one I possess.

No it would not be of any use for sizing bonding conductors as per Table 54.8 in BS7671.
35mm² 4 core, 50mm² 3 core and 70mm² 2 core would all have a CSA to satisfy the minimum CSA required for Table 54.8.
However would anyone consider using 50mm² or 70mm² cable where the minimum CSA bonding conductor is required?

 

[Engineer54]

Not saying theres anything wrong with tables, just saying you dont use the 8 - 1 ratio

Only when i think there's a need to calculate. More a case i think, of getting used to the numerous installations of SWA cables on the bigger projects. You get, what i can only describe as an instinct or gut feeling that there could be a problem with a particular cable run. Most of the time, the cable will still comply, ....but Just!!! But still happy that you did the calculation to prove that it warranted that extra effort... lol!!!

 

[Chr!s]

I dont have johns chart, i use the manufactures info or GN8.

My earlier posts were trying clear up the fact that there is a difference between the copper equivalent for steel, when calculating for a cpc and for that of a bonding conductor.

 

[Deleted member 26818]

Yes the requirement for a CPC is based upon the withstand capabilities of a material for a short duration at a high amperage.
Whereas for bonding conductors where PME conditions apply it is the withstand capabilities of a material for what could be very long periods at unknown amperages.

 

[Engineer54]

Chris,

I found this in the Sticky threads on this subject. It is the paper John Shepherd wrote that includes the table that Spin and i use a a good rule of thumb for guidance on the SWA CSA etc....



Using the armour of SWA.pdf

 

[Chr!s]

Whereas for bonding conductors where PME conditions apply it is the withstand capabilities of a material for what could be very long periods at unknown amperages.

Copper equivalent should be used for all bonding regardless of earthing arrangement