SWA used as CPC

[pepparz]

Is there a reference guide for which SWA sizes can be used as the CPC? I have a 120mm 4core SWA at 110M and although the Zs value has been measured at an acceptable value our electrical insurance inspector wants all SWA cables above 16mm on site (industrial premises) to have a seperate earth pulled in along side, is this right?

 

[Darkwood]

I typed 'swa as earth table' into google and was inundated with results... but to save you the hassle heres the table...

http://www.earthingnuts.co.uk/pdf/pvc_xlpe.pdf

Sorry for the sarcasm it probably took you longer to create this thread than a google search would have been lol, the 16mm and above is wrong as an across the board request but all '4core' swa up to 70mm will comply although if using 2 and 3 cores id be checking against this table.

The insurance company has made a blanket request because looking at 10mm 2c and 16mm 2 and 3core xple these don't meet requirements so rather than providing a table of compliance they have made a blanket rule.

According to the table 120mm 4core complies although its for you to work out the Zs value and whether it will be low enough by measuring the Ze and using cable calcs to estimate zs as you now know the SWA is equivalent or larger than required.

Print the table and explain which cables do comply that you may be fitting they may ease the blanket rule if they don't explain the client may swap insurers as there demands are beyond requiremnents of BS7671 which the industry follows .... that might do the trick.... if a company has to spend x amount upgrading cables that don't need to be then the company will may find it in there interest to swap insurers.

 

[davethsparky]

Ive heard this seperate CPC for anything over 16mm rule before, was it something that was genrally accepted a s a bit of an old wives tale years ago?

 

[telectrix]

i nthink a lot of this is due not as armour as cpc, but where a bonding conductor may have to be added if the armour is OK as cpc, but not sufficient to comply as a bonding conductor for extraneous bonding.

 

[pepparz]

thanks for your reply,i have already seen this table but was unsure if "it would stand up in a court of law" so to speak as i have to justify going against what our electrical insurance inspector advisors.but thanks again and i'll use this as a guide.

 

[Darkwood]

Its a good point Tel but OP says all cables 16mm plus require additional earth now what you say may apply to an outbuilding or separate unit but not as a blanket rule that his insurers have implied this would cost the industry a fortune in wasted Mat/Labour costs for work nt needed.

 

[telectrix]

Agreed. usually the case for separate bonding conductor if SWA is under 10mm. was just trying to explain where the myth came from. on the bigger cables, it's generally up to 95mm where the armour complies as cpc. as you rightly point out, the additional cost , if unnecessary, is stupid. some of these pen pushers have read some article that bears little relevance to the situation and misinterpreted it as to apply.

 

[Engineer54]

I typed 'swa as earth table' into google and was inundated with results... but to save you the hassle heres the table...

http://www.earthingnuts.co.uk/pdf/pvc_xlpe.pdf

Jesus, will people throw this old and confusing table in the bin once and for all, it's well past it's sell-by date!! Most of the cables this table states won't comply, actually will!! Just bin the bloody thing!!

For SWA used as the cables CPC, all cable sizes (be they of thermoplastic or thermosetting insulation) and core numbers (2 to 4 core) upto and including 95mm will comply. Only excessive cable lengths will have any effects on compliance.

The problems come only if the SWA is also being used as a main, or sub-main earthing conductor, where a building main bonding requirements has also to be met by the armour of the SWA cable!!!

 

[Darkwood]

Jesus, will people throw this old and confusing table in the bin once and for all, it's well past it's sell-by date!! Most of the cables this table states won't comply, actually will!! Just bin the bloody thing!!

For SWA used as the cables CPC, all cable sizes (be they of thermoplastic or thermosetting insulation) and core numbers (2 to 4 core) upto and including 95mm will comply. Only excessive cable lengths will have any effects on compliance.

The problems come only if the SWA is also being used as a main, or sub-main earthing conductor, where a building main bonding requirements has also to be met by the armour of the SWA cable!!!

The table is correct 100% correct... as for confusing im not sure what you mean as long as you de-rate your XLPE to 70c as it clearly states 90c .... please dont tell me we have to further simplify these things wheres the technical part gone from been an Electrician if they never do the calculations and get drip fed all the answers how can their be any competence anymore....
Ill agree though i should have pointed that out about the Temp' de-rating on the XLPE may show compliance using the adiabatic equation where due to the 90c rating it shows as a non-compliance.

 

[7029 dave]

not this old chestnut again!!

 

[telectrix]

chestnut? what about the carrot cake?

http://www.google.co.uk/url?sa=t&rc...GnjboO2Jk4S_jSUCINPShuQ&bvm=bv.51156542,d.d2k

 

[johnboy6083]

can I just add that the table uses the requirements of table 54.7 as its reference. If you use the adiabatic equation, then 99.9% of the time, the SWA will comply. The exception is on PME systems, where a main bonding conductor of upto 50mm maybe required on sub-mains to external buildings containing extraneous metalwork.

 

[joel89]

Ive heard this seperate CPC for anything over 16mm rule before, was it something that was genrally accepted a s a bit of an old wives tale years ago?

its 25mm and over. armourings can be used as earth conductor

 

[netblindpaul]

Is there a reference guide for which SWA sizes can be used as the CPC? I have a 120mm 4core SWA at 110M and although the Zs value has been measured at an acceptable value our electrical insurance inspector wants all SWA cables above 16mm on site (industrial premises) to have a seperate earth pulled in along side, is this right?

Not read the rest of the thread, however, IF you are going to pull in a separate cpc, then it MUST be capable of carrying the full fault current etc. it is NOT acceptable to use a reduced CSA.
There is also a table in GN1 that gives this information.
See Appendix D3.
If the insurance "inspector" is doing this design I trust he is competent to do so, I somehow doubt it.
There is NO requirement in BS7671 EAWR, PUWER98 etc. to do this.
However, your insurer can demand what they like, as long as they sign for the risk.
Remember insurance companies are profit making enterprises, only there to serve their shareholders dividends.

 

[7029 dave]

90mm should do lol