SWA for 3 Phase Installation

[NoSparks]

There seems to be a tendancy now to wire single phase installations with 3 core SWA and ignore the armour as a conductore. What is the favoured way of installing 3 phase? 4 core T&N wth armour as earth, or 5 core TN&E? Indeed, is 35mm 5 core generally available?

 

[benji]

Normally a 4core ,but if it was a long run you might have to run a seperate cpc so it might be an option to run a 5core if its in stock? also the cores might be white.So its down to calcs./spec./avai./& price

yours benji

 

[ajelec10]

I prefer to use 5 core, if you ask for colored cores they can get it, and its normally available but not from stock 2-5 days??

 

[Guest123]

Got to be honest 5 core swa is like rocking horse .... round my way.

 

[TF and the wire]

I suppose if cost is important there is nothing wrong with using the armouring, as long as the locknuts are tight and don't corrode, work lose, ELI reads OK etc. Using 5 core eliminates this possibility so I would always go for 5 core, and have no problem getting hod of it.

 

[Guest123]

Usually just run a seperate CPC myself.

 

[supasparxs]

I personally have never installed 5 core SWA and have only seen it once.

I can't see a problem in using the amour for a steel CPC and larger than 50mm cable running a seperated eath cable to reinforce the Ze

I think it comes down to personal choice,

I would say that if you base your costings for the more expensive option and the if the budget gets tight on the job, then you can change the spec for the cheaper option.

(this is assuming you haven't detailed the exact cable)

I think this is one for personal choice and there is no right or wrong answer

Richard

 

[NoSparks]

Thanks for all your answers. I think I'l use 4 core and check R1 vv R2 before going to the expence of running a seperate CPC.

Geoff

 

[Guest123]

If you check out some cable manfacturers websites there may be tech info on the mohm/metre resistance of the armour to help you with your calcs.


Some good info here

http://www.aeicables.co.uk/literature/CurrentRatings.pdf

 

[scotsparky]

theres a reat page in GN1 that tells you if the SWA will be suitable for a CPC cant remember the page if i remmember correctly above 35mm 4c a seperate cpc has to be run and also some 16mm. double check first.
as for usinf a 5c remember the cpc can be smaller than live conductors so a seperate cpc will be cheeper.

 

[NoSparks]

Thanks I'll see if I can find it.

Geoff

 

[john.irvine]

You should find this web site helpful, amongst the SWA tables is one that gives you the nominal area of armour and maximum resistance at 20 C.

http://www.prysmian.co.uk/export/sites/prysmian-enGB/attach/pdf/BS5467_07_09.pdf

Use the area of the armour and its K value with Table 54.7 on page 130 of the 17th ed this will give you a good indication of its sutability as an earth

 

[termite]

If the installation is TN-S it would be prudent to lay a CPC of the same cross-sectional area as the conductors in a 4-core SWA cable in addition to securely bonding the wire armouring.

 

[NoSparks]

I've checked GN1 and it makes it quite clear that 35mm SWA has not just a little bit more than the required CU equivelent armour, but much more than adequate. Using 5 core or an additional earth is therefore not a requirement.

Regards,
Geoff

 

[TF and the wire]

So long as the locknuts are tight and don't work loose.

 

[SparkyDave]

have been happy in the past to use 4 core although i find that 5 core often looks nicer and is generally a neater install.


although sometimes dependent on what you are doing the cost outways the pro's

 

[jamie-spark]

Any Hoo if incorporating a cpc within the swa there is still a reqirment to ensure the armouring is connected to earth

 

[scotsparky]

True Jamie nice to see the scots have it covered.
Th table in GN1 is exellent but be carefull about the type of cable used as there is a difference in K factors

 

[gaulty]

I was under the impression that over a certain size of swa you cant use the armour as an earth and a seperate earth needs to be run in, unless there's a core for ie 5 core. personally never used 5 core and usually run in a seperate earth if needed. but always make sure that swa armour is earthed.

 

[termite]

Thanks gaulty. Since the inception of 17th Edn. I have always run a suitable seperate CPC alongside TP&N 4-core SWA buried cables and also for 3-core TP cables. Most of my work is on rural services for private pumped water supply installations, so longer power supply cables are the norm in our business as water engineers. I think that your take on this shows a responsible attitude to earth bonding.

Regards, termite.

 

[Knobhead]

It's a pitty SWA cables are so crap now. Under M&Q and foundry regs no CPC is required. The cables had 1 tinned copper to 3 steel wires in the armouring. Better still install PILCDWA the return path was often better the conductors

Thank god I've retired

 

[NoSparks]

OK. GN1 specifies that for 35mm SWA the armour is an acceptable CPC. But here comes the runt.
Irrespective of the Regs, (or is it in very strict adherence of the regs?) the MET must be at the supply head and the main bonding must run to the MET. It is unacceptable, and they will NOT provide a connection, if the bonding is to a Dis Board fed from a sub main.

Also, tails of more than 3 meters are Unacceptable. If the tails would be more than 3 meters then you have to install a single way DB (switch fuse or other) within 3 meters and take the sub main from that. More over, and contarary to the EDF web site which only requires an isolator, but only in some areas, it must contain fuses (or I suppose some other form of cutout) . The Reason... "so that they do not have to change their fuses if there is a fault with the sub main". ... Sounds rediculous to me because there is no discrimination, however that is their requirement before thay will connect a meter.

 

[mogga]

http://www.earthingnuts.co.uk/pdf/pvc_xlpe.pdf swa earth sizes for armours

 

[Andy Greaves]

I was under the impression that the tables in GN1, that refer to sizes of armourings in SWA, were an indication to whether the armourings comply with table 54.1 (54G in 16th). If the armourings do not comply then the adiabatic equation needs to be done in order to ascertain whether the armouring are capable of taking the current produced under earth fault conditions.