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

 

[nathansinar]

I have seen another thread like this one posted on here from a while ago where some electricians are debating it saying they just cut it back and tape it? its seems like many people do it without earthing the braid. as i said its certainly not the best way but surely if it was breaking a reg no one would do it?

 

[GMES]

That is rather scathing, can you provide any documentation which states the braid is to be earthed for LV applications. Then perhaps you can issue it to the trade to safe further confusion.

What are you saying mate? im just gonna re ask the question at work today most people are saying its a must do sorry if you mean the same , just trying to understand your post
Cheers

Nathan,I think Westwards reply was to Darkwoods comment and not your comment.

 

[KennyKen]

SY or EMC over in Aus. Should only really be used for a motor supply which has been wired to the Load side of a VSD. The Braiding reduces Harmonic interference and to a certain degree concentric although I've only used the correct metal glands which bite onto the braid and NOT used the sheath as a secondary Earth. Using this Type of cabling for sockets is definitely not the greatest choice.

 

[nathansinar]

From my picture though using the plastic gland and not earthing the braid does it break regs or? its just a way ive seen it commonly done

 

[KennyKen]

Its poor practice.

 

[westward10]

From my picture though using the plastic gland and not earthing the braid does it break regs or? its just a way ive seen it commonly done

Until someone finds solid evidence it should be earthed then no, however I would make the cable off so the braid is not exposed. People cite good practice but good and bad practice is personal unquantified opinion. If you are going to earth the braid to provide protection should it become live through damage you then have to question its capability for carrying fault current.

 

[Darkwood]

That is rather scathing, can you provide any documentation which states the braid is to be earthed for LV applications. Then perhaps you can issue it to the trade to safe further confusion.

When you design an installation you are doing so with all the environmental influences in mind, given this then choosing SY as oppose to a normal flex/cable must have a particular design advantage and usually as is the design of the cable this is often utilised as a braided cable for screening purposes IE control wire, if however you are treating this braid as a form of armour (forgetting it no longer is recognised by BS 7671 for the moment), then you must apply the same standards you would to any other cable with an external conductive armour/sheath thus unless you are doing SELV it should be earthed for safety reasons... the regulations are general guidance and rarely go to the extent of been specific for certain set-ups so its a matter of applying common sense with the broader general guidance of the BS7671.

Like I pointed out earlier, imagine the cable been damaged or pierced by an object that comes into contact with the phase conductor, this could energise the braid and unless it is suitably earthed then this is a very dangerous situation, I don't understand how you expect me to quote specific regulations of a cable that is not recognised by the BS7671 standards either, the fact that it is no longer recognised means it is a cable that will not be addressed by the regs so you are tasked with using other standards to show the suitablility of the cable and also the safe installation and use of it.

 

[westward10]

Until someone finds solid evidence it should be earthed then no, however I would make the cable off so the braid is not exposed. People cite good practice but good and bad practice is personal unquantified opinion. If you are going to earth the braid to provide protection should it become live through damage you then have to question its capability for carrying fault current.

Which other Standards should we refer to. As in my previous Post how do we calculate the braids adequacy for carrying fault current.

 

[Darkwood]

Which other Standards should we refer to. As in my previous Post how do we calculate the braids adequacy for carrying fault current.

When using a cable not recognised by the BS7671 then that's up to you to show it will be suitable, I use specialised cable all the time for machinery installs that fall outside the BS7671 and I have to supply the relevent standards it is made to and sometimes the manufacturing characterisitics of the cable to show its suitablility for the job, so on that plain of thought it is up to you to contact the manufacturer and ensure the braid can handle the fault current, if it cannot then you should not be using it for LV installs, this is one of the main reasons it is not covered by the BS7671 as it is made under different standards for a very different purpose, some SY uses a tight weave braid where others use a looser braid that only partially cover the internal sheath, I would suggest the latter would be unsuitable for any LV use unless installation methods protected the cable from mechanical damage.

 

[westward10]

I personally won't give the stuff van space. Earthing the braid poses as many questions as not earthing it and the chance of any manufacturer providing guidance is remote. I could be wrong but I am sure the earthing glands are a post product to give a solution to a problem no one can give an answer to. Amen.

 

[Darkwood]

SY has been out decades and so have the glands, the problem was people starting using it as a armoured flex, something it most definately is unsuitable for, Im sure we have all seen this used as an extension cable, cracked, rusted braid and stiffened from oil ingress and the likes.. it clashed with the introduction of quick fix courses, dumbing down of the larger courses so we saw an explosion in its use as the very people using the cable were not correctly spec'ing it and ensuring its suitablility as the previous generations would have done as a matter of routine...there is this worrying trend that if you can buy it from an electrical wholesalers then its fine for general use attitude, people no longer seem to spec' cables or any other goods for that matter like they use to and worringly believe those behind the counter know what its good for.

 

[LeeH]

SY or EMC over in Aus. Should only really be used for a motor supply which has been wired to the Load side of a VSD. The Braiding reduces Harmonic interference and to a certain degree concentric although I've only used the correct metal glands which bite onto the braid and NOT used the sheath as a secondary Earth. Using this Type of cabling for sockets is definitely not the greatest choice.

But...

SY is a poor cable for EMC compliance as you cannot buy it with 3 cores that only phase coloured. 1 is always G/Y and the phases should be symmetrical.

Go figure..

 

[Darkwood]

But...

SY is a poor cable for EMC compliance as you cannot buy it with 3 cores that only phase coloured. 1 is always G/Y and the phases should be symmetrical.

Go figure..

why can't you get a 3core and earth then they come both versions phase coloured or numbered black cores, not sure where your coming from here either a 2c and earth could not be utilised for a 3ph supply as it would still require an earth and the braid should not be used as the circuit protective conductor although like I said earlier, it should be earthed in LV use.

 

[westward10]

why can't you get a 3core and earth then they come both versions phase coloured or numbered black cores, not sure where your coming from here either a 2c and earth could not be utilised for a 3ph supply as it would still require an earth and the braid should not be used as the circuit protective conductor although like I said earlier, it should be earthed in LV use.

You keep saying it should be earthed but you are not supplying information where this can be clarified.

 

[telectrix]

You keep saying it should be earthed but you are not supplying information where this can be clarified.

it's an exposed conductive part, therefore it must be earthed.