Sy cable question

[nathansinar]

Hi guys new to the forum and will introduce myself shortly

I have attached an image of a spur i have taken as you can see from the attached image

I am doing a trainee maintenance engineer role and just wanted some info on the below.

1.) when using sy cable do you have to earth the sheeth? i have had various reponses saying it is good practice but you can get away with using the cpc inside the cable and that alone?

2.) in the image i have posted becuase the sheeth hasnt been used an earth from the the spur to what ever it is feeding, does an earth need adding from the back of the spur plate to actual spur box as it could become live?? is it a reg that this needs to be done?

Thanks for help!

Nathan

 

[westward10]

I understand what you are saying @westward, and this is the very point I have been trying to make, if you wish to use SY then because it falls outside the BS7671 then its down to the installer to confirm if the braiding will be adequate to carry a fault current, the stuff I have used in the past has met this criteria as I have sourced the manufacturing info myself but I cannot say this is the same for every piece of SY out there, but I would say its best to earth than not to, given that even if it does take damage under a L/E fault then it should still trip the OCPD and investigation to why the circuit tripped should see it taken out of service anyway.

Yeah I know you get the drift, interesting you find it acceptable the braid may suffer damage under fault conditions, this is not acceptable and is the point I am trying to make.

 

[andyb]

Yeah I know you get the drift, interesting you find it acceptable the braid may suffer damage under fault conditions, this is not acceptable and is the point I am trying to make.

It's not really the point whether the braid will suffer damage, but that without earthing it a fault such as a nail penetrating the braid and live conductor will be live.
Not only that but the braid will be live along the whole length of the installation.

 

[westward10]

It's not really the point whether the braid will suffer damage, but that without earthing it a fault such as a nail penetrating the braid and live conductor will be live.
Not only that but the braid will be live along the whole length of the installation.

Isn't it, the braid should maintain it's integrity under fault conditions so the circuit disconnects whether the cable is no longer serviceable or not. It seems to be the case for all other circuit configuration unless SY is involved, just earth it job done no thought required.

 

[andyb]

Isn't it, the braid should maintain it's integrity under fault conditions so the circuit disconnects whether the cable is no longer serviceable or not. It seems to be the case for all other circuit configuration unless SY is involved, just earth it job done no thought required.

Defiantly not. If the braid is an exposed conductive part then it will need to satisfy the regs regarding disconnection time if a fault occurs. This may be earthing it, it may require an rcd. If you can't guarantee the disconnection time then it should not be used.
So you see, lots of thought.
Just ignoring it because you're not sure that it can maintain it's integrity under fault condition would come under the heading 'no thought required'

 

[westward10]

Defiantly not. If the braid is an exposed conductive part then it will need to satisfy the regs regarding disconnection time if a fault occurs. This may be earthing it, it may require an rcd. If you can't guarantee the disconnection time then it should not be used.
So you see, lots of thought.
Just ignoring it because you're not sure that it can maintain it's integrity under fault condition would come under the heading 'no thought required'

Whether it is an exposed conductive part is debatable. As a matter of interest how are you assessing the braids ability to carry fault current whilst suffering no thermal stress.

 

[andyb]

Whether it is an exposed conductive part is debatable.

Indeed it is. I do say in my first post on the subject 'If the braid is an exposed conductive part'
'

As a matter of interest how are you assessing the braids ability to carry fault current whilst suffering no thermal stress.

I'm not, I wouldn't know how to. I imagine there will be substantial thermal stress and damage with a fault to earth. There is on everything else.

What I'm saying is that if the braid is an exposed conductive part then a fault would need to disconnect the supply in .4 sec. assuming a TN supply.

 

[westward10]

There lays the problem which probably explains why this cable should not be used.
There should be no damage under fault conditions if conductors are correctly selected.

 

[andyb]

I don't use it either Westward, if you say that the braid is not an exposed conductive part and leave it, then someone puts a nail through the braid and live then it will always be live. Then if someone drops a socket as in the picture in the OP you can see the problem. Metal box, live braid, hold the box with one hand and touch the braid with the other it will hurt. Coupled with the fact that I assume there is no rcd protection to that circuit ( rcd socket) it could be very nasty. Also looking at the picture I assume that particular circuit is live as the rcd is holding in.

 

[sparksburnout]

Im just stating what a proper sparky has told me... the regs dont state that they have to be glanded like that? i agree earthing the sheeth is better but its not compulsory? and in the image shown does an earth need to be run from the back of spur plate to the actually box??

Thanks

Could I just ask a question? You have stated "this is something I did earlier this week" but you obviously don't really know what you are doing, why are you not looking in "the regs" or asking the person that is training you? Your post doesn't really seem to make much sense to me. Are you really a trainee? Or just "having a crack" at it? Just saying.....

 

[KennyKen]

The Cable is Concentric. If the proper SY glands are used between two metallic enclosure's. Then you wouldn't need to Earth the braid. Although I've never used this cable for sockets.

 

[Barry White]

Post 29 I got a bad electric shock from this type of cable the braid was live it was on a farm and the ground and me were wet .
If it had been earthed it may have tripped or it may have just burned off the fault who knows but at least I would not have had a shock.

 

[andyb]

The Cable is Concentric. If the proper SY glands are used between two metallic enclosure's. Then you wouldn't need to Earth the braid. Although I've never used this cable for sockets.

Assuming you mean earthed metallic enclosures then surely that would earth the braid Kenny. Or am I missing something?

 

[KennyKen]

Yeah too many opinions. I've used the cable for control/motor applications. That being said if it's being used to supply sockets then having a physical Earth from the braid is plausible. I think we can all agree that SY shouldn't be the chosen cable for said Install

 

[KennyKen]

Assuming you mean earthed metallic enclosures then surely that would earth the braid Kenny. Or am I missing something?

Of Course. The metallic enclosures would need to be earthed. I'm only basing my opinion on what I've used the cable for. I wouldn't use SY for Sockets. If I were then yeah I would probably create a physical Earth using the braid

 

[Darkwood]

I too have come across this cable in a poor condition hundreds of times but on 2 occasions the braid was live, this is over the last 5yrs so its worrying the impropoer use this cable is subject to, I'm on a site at the moment who have there own sparks and the sockets are in SY although they have maintained the braiding throughout by strapping it down at every end and point, I don't have issue with what they have done although I question the cable choice given its a factory environment, we have better methods for such installs.