Outdoor cable

Steve

I need to hang a cable outdoors across a 4m gap.

I'm going to install a catenary wire & turnbuckle between the structures to hang it from.

Is there anything I should look out for?

I'm thinking a moderate hanger wire tension in cold weather should be fine. 200mm loop each end on the electrical cable for expansion / contraction.

I don't really want to use SWA as the bend radius wont suit - is Silflex or TRS ok for outdoors?

Any other ideas?

240V/20A/ 3*4sq needed.

2011

I would use an SWA, the bending radius is about 6 times its diameter. As 3 x 4sq has an OD of slightly less than 15mm it can be bent quite tightly.

Silflex (SY cable) can only be used if the sheath is made using UV stabilisers (not always the case). Outdoor installation is, in general, not recommended.

Also once the cable is supported with plastic tie wraps I would recommend that plastic coated stainless steel tie wraps are used. This will ensure that the cable remains supported in the event of the plastic tie wraps failing which can happen when a cable is hanging from them that sways.

Steve

That link seems to rate the cables way more than I expected.. 38A for 1.5?? surely thats not right!

I'll have a CPD of 20A and about 15m total run.. maybe 2.5 will do.

Although, price difference will be not much for swa so I think I'll stick with 4sq.

That site seems only to have BN/BU for single phase.. I thought you had to have a PE conductor as well as the SWA bonded?

2011

Steve wrote: »

That link seems to rate the cables way more than I expected.. 38A for 1.5?? surely thats not right!

Definitely not. The link no longer works for me.

I'll have a CPD of 20A and about 15m total run.. maybe 2.5 will do.

Although, price difference will be not much for swa so I think I'll stick with 4sq.

A better job.

That site seems only to have BN/BU for single phase.. I thought you had to have a PE conductor as well as the SWA bonded?

Almost without exception, yes

Steve

It's a UK site, maybe they haven't caught up to modern regs yet

I'll talk to my supplier, thanks a mill for the info.

Man11

Steve wrote: »

I need to hang a cable outdoors across a 4m gap.

I'm going to install a catenary wire & turnbuckle between the structures to hang it from.

Is there anything I should look out for?

I'm thinking a moderate hanger wire tension in cold weather should be fine. 200mm loop each end on the electrical cable for expansion / contraction.

I don't really want to use SWA as the bend radius wont suit - is Silflex or TRS ok for outdoors?

Any other ideas?

240V/20A/ 3*4sq needed.

Nym should be fine just use waterproof boxes when needed
Trs should work too but nym is fine

Steve

Man11 wrote: »

Nym should be fine just use waterproof boxes when needed
Trs should work too but nym is fine

Waterproofing wont be an issue but NYM is solid as opposed to flex so not suited to hanging on a catenary wire - it will eventually fail because of movement.

2011

Man11 wrote: »

Nym should be fine just use waterproof boxes when needed
Trs should work too but nym is fine

No, NYMJ is not UV resistant.
Check the data sheet.

Man11

Steve wrote: »

Waterproofing wont be an issue but NYM is solid as opposed to flex so not suited to hanging on a catenary wire - it will eventually fail because of movement.

Sorry their . Trs then . I know he said not swa but surely that's better

Man11

2011 wrote: »

No, NYMJ is not UV resistant.
Check the data sheet.

I have nym out side perfectly fine

Steve

What do ESB use from a pole to a house? I thought that was TRS?

Man11

Steve wrote: »

What do ESB use from a pole to a house? I thought that was TRS?

Do you what I think your right

Steve

I will, thanks

2011

Man11 wrote: »

I have nym out side perfectly fine

With all due respect that does not make it suitable for the application or compliant with regulations.

Outdoor usage is only possible as long as the cable is protected against direct sunlight.

Man11

2011 wrote: »

With all due respect that does not make it suitable for the application or compliant with regulations.

Outdoor usage is only possible as long as the cable is protected against direct sunlight.

Yes I know that I said it earlier on . No need to be smart here .

2011

Man11 wrote: »

Yes I know that I said it earlier on . No need to be smart here .

Im not being smart.
I simply don't see where you acknowledge that theses cables are not resistant to UV.

Man11

2011 wrote: »

Im not being smart.
I simply don't see where you acknowledge that theses cables are not resistant to UV.

If you go back I said sorry to the man . I was getting mixed up .

2011

Man11 wrote: »

I was getting mixed up .

It happens to all of us

Risteard81

Steve wrote: »

It's a UK site, maybe they haven't caught up to modern regs yet

I'll talk to my supplier, thanks a mill for the info.

It is permissible to use the armour as a cpc so long as you prove it's suitability with the adiabatic equation to demonstrate that it will withstand the fault current until disconnection occurs (and check loop impedance) so 2-core SWA is suitable for single phase applications.

2011

Risteard81 wrote: »

It is permissible to use the armour as a cpc so long as you prove it's suitability with the adiabatic equation to demonstrate that it will withstand the fault current until disconnection occurs (and check loop impedance) so 2-core SWA is suitable for single phase applications.

Yes, you are correct.

However this is generally not th approach that is taken as there are many factors that can negitively impact on the impedance of the armour. These include:
● Loosening of SWA glands
● Corrosion of cable armour. This often occurs at the point that the cable is glanded.
● The quality of the earth to the trunking / gland plate / panel that the cable is glanded into deteriorates.

In many industrial applications / plants the site standards will insist on a separate CPC (earth cable) being run. These standards must be adhered to in addition to the local regulations. In fact the trend at present is to increase the CPC size.

Risteard81

There is no question that using armour as a protective conductor is a practice which has fallen out of favour in recent years, and specifications often require an extra core or separate conductor. I was simply challenging the very common (yet incorrect) view that there is a prohibition in the Wiring Rules.

Bruthal

2011 wrote: »

Yes, you are correct.

However this is generally not th approach that is taken as there are many factors that can negitively impact on the impedance of the armour. These include:
● Loosening of SWA glands
● Corrosion of cable armour. This often occurs at the point that the cable is glanded.
● The quality of the earth to the trunking / gland plate / panel that the cable is glanded into deteriorates.

In many industrial applications / plants the site standards will insist on a separate CPC (earth cable) being run. These standards must be adhered to in addition to the local regulations. In fact the trend at present is to increase the CPC size.

I always felt that using the armour as a cpc was a makeshift setup. Too many components need to be correctly completed, and even then, they can change over time, (corrosion etc).

Risteard81

Bruthal wrote: »

Too many components need to be correctly completed, and even then, they can change over time, (corrosion etc).

If you only use CW glands and never BW glands then there is seldom any problem with a correctly glanded cable.

Bruthal

Risteard81 wrote: »

If you only use CW glands and never BW glands then there is seldom any problem with a correctly glanded cable.

That's hard to say really. It's not self monitoring, so the very simple direct from earth bar to earth point out on the circuit, is far preferable.

I don't know how many times I seen lock nuts loose on glands. Even though the glands themselves were done correctly. Sometimes ye have to look beyond what rules say, simply because in some cases, the simple is far better than the less simple. And an earth via a dedicated conductor is far easier to be made positively good, than via armour, glands, banjos and nuts/bolts.

2011

Risteard81 wrote: »

If you only use CW glands and never BW glands then there is seldom any problem with a correctly glanded cable.

But this only addresses one of the possible issues that could impact on the impedance of the armor (see my last post).
Although technically you are correct using the armor as a CPC is not the norm.
I would consider it bad practice and would advise against it.

2011

Bruthal wrote: »

That's hard to say really. It's not self monitoring, so the very simple direct from earth bar to earth point out on the circuit, is far preferable.

I don't know how many times I seen lock nuts loose on glands. Even though the glands themselves were done correctly. Sometimes ye have to look beyond what rules say, simply because in some cases, the simple is far better than the less simple. And an earth via a dedicated conductor is far easier to be made positively good, than via armour, glands, banjos and nuts/bolts.

+1

Unfortunately properly installed glands can loose from vibration or from someone bending the cable and / or pulling out of it in an attempt to get a drill in to drill a hole for and additional cable. Sometimes it is impossible to tighten a lock nut on a loose gland as the trunking/ panel is so packed that access is simply impossible.

Bruthal

2011 wrote: »

+1

Unfortunately properly installed glands can loose from vibration or from someone bending the cable and / or pulling out of it in an attempt to get a drill in to drill a hole for and additional cable. Sometimes it is impossible to tighten a lock nut on a loose gland as the trunking/ panel is so packed that access is simply impossible.

And that's in a steel trunking that can be drilled and banjo securely bolted. Try it inside a plastic isolator.

There is no doubt a good CPC can be achieved through the armour, but its far simpler and more reliable with a dedicated earth conductor.

Tuco88

Unless you have those beautiful ex isolators, with the treaded earth plate inside... And top if off with a hawke gland to match, tossing the banjo and shroud away while laughing like a mad man.

I think it's ny-jj is the outdoor uv rated version of nymj. Tho I have never used it.

Hight tuff, I have used its uv rated essentially SWA without the W.

I do find some electrical suppliers can lack on a decent cable selection.

Risteard81

Bruthal wrote: »

And that's in a steel trunking that can be drilled and banjo securely bolted. Try it inside a plastic isolator.

Again the armour can be securely earthed via the gland and banjo in a plastic enclosure, however it is recommended that the banjo be sandwiched between TWO locknuts within the enclosure to prevent it becoming loose due to plastic creep. This ensures an adequate metal to metal contact.

There is no doubt however that metallic enclosures give a better connection (although Wiska boxes can be supplied with an earthing plate for SWA, and Piranha style locknuts can also be used).

Risteard81

Tuco88 wrote: »

Hight tuff, I have used its uv rated essentially SWA without the W.

Hi-Tuff is quite widely used in the north, however it shouldn't just be used where SWA was specified as it does not have an earthed armour! And it must be remembered that regardless of extra cables/conductors being used with SWA as a protective conductor, the armour is an exposed conductive part and MUST be earthed.

Bruthal

Risteard81 wrote: »

Again the armour can be securely earthed via the gland and banjo in a plastic enclosure, however it is recommended that the banjo be sandwiched between TWO locknuts within the enclosure to prevent it becoming loose due to plastic creep. This ensures an adequate metal to metal contact.

There is no doubt however that metallic enclosures give a better connection (although Wiska boxes can be supplied with an earthing plate for SWA, and Piranha style locknuts can also be used).

Like I said, a makeshift way to provide a CPC when it can simply be done with a conductor. Anyone who thinks banjos inside plastic isolators are neat and easily fitted, havnt done too many.

They are awkward, and tedious particularly inside smaller ones, to such an extent that most will put one locknut on, tighten as best they can, and move on. Earth the armour via the supply end of cable, and a CPC conductor to do the field earth terminal IMO is better.