swa earthing

[normspanners]

I am doing some work in an old barn and it has had 3 ph brought in with a new sub main metal CU, with an mcb,s then split down with a 1ph radial and IIRC they have used 6mm (Could be 10mm ) 4 core swa for 3ph and neutral run to the plastic 4 pole rotary isolator, that I am connecting to, but the sparky has used only the swa's armour with standard glands as the earth from the CU, I know this was the old way but thought it had been outlawed and should have a separate earth conductor ie usually 5 core cable.
I called in today to get a 16 a 5 pin switched socket from wholesalers and asked several electricians and was shocked that NO-ONE could answer the question??
Also he has used modern coloured cable so it was bought in to do that job !!

 

[winchman]

If it bothers you fit another Earth cable along side it.
You really need to read the 17th Edition regs to be certain, but I have seen this before, My garden lights use three core (as it was free) but I have also connected the earth to the armour as I see no reason not to ( unless its data cable then it can cause issues)

 

[Spark plug]

There is no specific requirement to use a dedicated earth as the steel armour meets the minimum earthing requirements.

But in some cases I find it best practice to have a dedicated earth, say when a cable is buried and there is a possibility of the steel becoming corroded.

 

[WorkshopChris]

It only needs an additional earth in some rare situations, from memory you can look the cpc csa up the the charts and will probably only need an additional earth core if using something with very slow disconnection times. D rated breaker possibly.

 

[dobbslc]

If it's glanded into a plastic dist board or isolater you need to fit the brass banjo to the gland and run an earth flylead off of it to your earth terminal. It perfectly ok to do this. Use the same size as the main cable cores.
Obviously both ends need connection to earth.
Even if you're not using the swa as an earth the regs state it MUST be grounded in case it gets damaged. ( If that happens it's possible for a nail to go in and hit the un grounded swa wire and a live core and this will then leave the whole cable live under the insulation!
Some sizes of swa don't comply with the minimum earthing cross sectional area but as far as I can remember that's 95mm and other larger sizes.

 

[dobbslc]

I'll also say the "electricians" you spoke too in the wholesalers were probably just some of the new wave of chancers flooding the industry. They do a 2 month course and think they're fully qualified electricians.
That question is a basic one that they should be able to answer.

Rant over.... for now!

 

[zzr1200]

It only needs an additional earth in some rare situations, from memory you can look the cpc csa up the the charts and will probably only need an additional earth core if using something with very slow disconnection times. D rated breaker possibly.

 

[normspanners]

Thanks guys for clearing that up , it seems that if you speak with different sparkies and they all have their own take on it, some not so well informed for instance I spoke with one who said he allways runs seperate cpc. because it was required by 17th
I have found this https://www.gadsolutions.biz/regulations/swa-as-the-cpc seems other people in the industry are a little confused too ?

http://www.earthingnuts.co.uk/pdf/pvc_xlpe.pdf shows there are some odd small sizes of xlpe that are very close and are in the red?

Also some questions on electritians forum http://www.electriciansforums.co.uk/threads/can-we-use-the-armour-of-an-swa-as-the-cpc.23288/

 

[IanJ88]

There is nothing wrong using the SWA Armour as the earth, as long as the correct glands are used and they are tight, we use this method of earthing for Street Lighting Applications.

 

[nick952]

With plastic enclosures and SWA, it's good practice to fit and tighten the gland with one Nut, then fit the brass banjo and then clamp this with another nut on top. This is because over time the plastic "creeps" due to the pressure of the nut and both the gland and banjo can come loose. Clamping the banjo between the two nuts keeps it tight on the gland, even though the gland itself, may have come loose in the enclosure.

 

[normspanners]

With plastic enclosures and SWA, it's good practice to fit and tighten the gland with one Nut, then fit the brass banjo and then clamp this with another nut on top. This is because over time the plastic "creeps" due to the pressure of the nut and both the gland and banjo can come loose. Clamping the banjo between the two nuts keeps it tight on the gland, even though the gland itself, may have come loose in the enclosure.

Cheers Nick good idea

 

[dobbslc]

That's the chart I use, we only use 4 core so that's why I had the 95mm cable in mind!
Nick that's a good idea with the glands and plastic enclosures although some are so thick there's not enough thread left on the gland to get a second nut on.

 

[Robotstar5]

With plastic enclosures and SWA, it's good practice to fit and tighten the gland with one Nut, then fit the brass banjo and then clamp this with another nut on top. This is because over time the plastic "creeps" due to the pressure of the nut and both the gland and banjo can come loose. Clamping the banjo between the two nuts keeps it tight on the gland, even though the gland itself, may have come loose in the enclosure.

On plastic enclosures I prefer to use earth nuts, it's the way forward

 

[brightspark]

That's the chart I use, we only use 4 core so that's why I had the 95mm cable in mind!
Nick that's a good idea with the glands and plastic enclosures although some are so thick there's not enough thread left on the gland to get a second nut on.

then u screw the armoured gland in to a coupling with earth tag in between then fit a brass male gland through the plastic db in to the coupling

 

[Can'tWeld]

I came across this myself recently into a metal cased CU and wondered about it then; no flylead or anything, just continuity from SWA earth to case and then from case to earth bar via the metal mounts. Was told it was fine to do it that way but it does strike me that it's a bit vulnerable to 'operator error', i.e someone forgetting to clean the paint off around where the bolt goes through the case from the earth tag

 

[Spark plug]

I have worked in old commercial installations ware all enclosures, sockets, switches, light fittings etc etc where metal and all linked with steel conduit. There wasn't an earth wire any ware, had me scratching my head for a while.

 

[WorkshopChris]

I have worked in old commercial installations ware all enclosures, sockets, switches, light fittings etc etc where metal and all linked with steel conduit. There wasn't an earth wire any ware, had me scratching my head for a while.

Had a fault that we couldn't find in an old factory all steel threaded conduit and cast iron enclosures with wire wound fuses.
Only earth wire in the building ran from the main switch to the incoming water pipe below.

The only indication at first that there was a fault was some but not all exposed steel gave some people but not everyone a very slight tingling sensation when touched. But if you put your hands under one cold tap at the far end of the building you could feel something but the biggest clue was steaming hot water straight out of all the cold hot taps.

At first we had the water board out they had never seen anything else like it, as it was thought it was an underground external fault.
After a few hours testing we found a screw in a socket box had eventually squashed the insulation and made a short direct to earth. But the resistance of the steel conduit was to high to blow the 30a fuse wire. The main earth cable was passing roughly 20a directly through to the incoming steel water pipe, turning it into a huge heating element.

 

[normspanners]

After a few hours testing we found a screw in a socket box had eventually squashed the insulation and made a short direct to earth. But the resistance of the steel conduit was to high to blow the 30a fuse wire. The main earth cable was passing roughly 20a directly through to the incoming steel water pipe, turning it into a huge heating element.

That was costing a few pounds in unit's

 

[normspanners]

Have spoken with quite a few (in theory) well thought of sparkies recently when they have come into the garage etc and the answers are alarmingly different as to what ACTUALLY IS the requirement ranging from what is correct ie as stated in this thread, to OH NO, you now HAVE to have a seperate copper cpc because the 17th demands it.
is it the fact that they dont actually read the regs, just listening to hearsay? -----------or cant be bothered???.
This would be similar a little like, say------ some of the road rules changing (maybe) bus lanes etc and people just listening to hearsay some doing it some not, but the ministry dont actually produce a book, so people have difficulty actually KNOWING the facts, a book like the 17th as they do for the leccie reg's

 

[Spark plug]

The probloem with the regs is that they are wrote in sutch a manner that they can be applied to any situation and eventuality.

Therefore they are open to interpretation and to make things even more fun there is often 2 or more regulations that can be applied to 1 situation, which contirdict each other.