Earthing Cable with the Armoured Power Cable (Hv/Lv)

You might try searching, before asking someone else to do your work for you!!

ISO - International Organization for Standardization

Not if one of the conductors inside the armour were an earth conductor.

There are very few international electrical standards, as there are so many countries, each of which has a slightly different way of doiing things.

In the absence of an international standard, some countries use British Standard 7671, particularly where the suply is 230VAC 50Hz.

Not quite true as you know nothing of the system voltage, cable type, (3 or single core), earth fault currents for the area and if this is in a sub station, duct, trench or cable rack. This lad has offered no details, so your inofrmation is totally irrelevant, either in the UK or USA or anywhere. He needs to check his own regs and know what he is working with. And, all steel wired armour cables should be mechanically glanded off, to a steel gland plate, which is earthed. Standard practise incase the cable is struck by a digger machine, pick or shovel. Even short run lengths need the armour earthed solidy. (At one end for the least). Personnel protection.

<...nothing of the system voltage, cable type, (3 or single core), earth fault currents for the area and if this is in a sub station, duct, trench or cable rack..>

- a situation shared with the whole of the rest of the forum at this time.

If the cross section and material of armour is sufficient/satisfactory to carry the fault current till it is interrupted why don't you use it for earth continuity?. Check standards/codes.

Yes there are standards, and yes you should run a earth cable.

Standards... you need to find the one that applies to where you are, or adopt a known standard.

Why run a earth core? Depends on if you armour has the csa to carry the fault current. It was common practice many years ago, however the armour is just that... armour to protect the cable against mechanical damage. Furthermore, as in many cables the armour is some sort of lightly protected metal , and the SWA cable gland was brass, in a right conditions corrosion would occur where the gland gripped the armour, rendering your earth path to almost nothing. So to be sure you have your item earthed.. run a earth conductor

Thanks brich

Can you give me the standard reference as it is in IEC or IEEE/NEC with reference number.

My friend.. the short answer is NO!

Why?

Because if you can find CR4, then you are clever enough to find the standards, and you will remember.

If you need help with those standards, yes I will if possible help, but I refuse to do your work for you!

Are you on the same grumpy pills I am on?

sure am!! 1000mg twice a day!! makes me grumpier than a water buffalo with a tick up its butt!!

Clarification please.

Is it tick?

Tick!

Small biting insect, that can leave an infection, or pass on infections.. Hence grumpiness of water buffalo and Welshmen stuck in a hot, dry Libyan desert.

for further explanation please go to Wikipedia!

Agreed, the SWA is for protection, but if it is NOT earthed and the SWA is damaged by a JCB bucket, and the bucket tooth hits a live core, the system does not trip! One live JCB, one fried operator. Fact! The armour gets earthed by some means and a mechanical gland is best, if you know how to install it properly. Old days we used lead wipe glands, Armour and lead connected to the gland. I wonder why we went to so much hassle? Did we know something then, we dont know now?

As most SWA glands are metal (brass or S/S) and usually fixed to a metal box and the metal box would hopefully be earthed, the armour would be earthed. In the case of the box being made of a non-conducting material such as fibreglass then a earth washer would be used and the armour would be bonded to the most suitable earth point, using an earth cable with a suitable csa. That would be sufficent to earth the armour and prevent your fatal accident, would you not agree?

I did not say that the gland was not earthed, did I?

The SWA is looked upon as a supplimentary earthing and not to be confused with the main earth of any cable or supply. Previously before gland earth washers for SWA cables, a small section of the outer insulation was removed and an external earth clamp was connected to the armour, and if jointing a large "pilcswa" cable, the cast iron joint box was also earthed.. but I digress..

Quite.

No, you are correct, you stated; ...metal box would hopefully be earthed.. I think this was what you stated. It either is earthed, or it is not earthed. There are no half measure when earthing a system. Won't argue a meaningless point but will agree with you, 'the armour would be bonded to the most suitable earth point, using an earth cable with a suitable csa'. Cheers.

like I said.. 'hopefully be earthed'.... but that really depends on who has installed the box, cable...etc.

Having worked all over the world.. I cannot begin to describe what I have seen as a 'safe' electrical installation.... hence the word.. 'hopefully'..

One can only hope!

It seems there are many lazy folks out there waiting for others to do alltheir work. Have you tired checking any standard? Do you even know what your earth fault currents are for the installion? If you knew these simple facts you might calculate the armour wire size, armour wire type, Galv versus copper and you might add details of your system voltage, cable type, soil type, run lengths, before asking for miracles. Perhaps we should charge for services rendered or issue certificates. Did anyone teach anything at college or Uni. Did you listen to what was informed to you. First stop; check your own requirements, 2nd stop;know what standards you utilise, 3rd stop; check your current standards, 4th stop; know the system you are working on.

Good advice is found here, but only you can stop yourself being killed. Lyn may be sarcastic, but he has a valid point.

And I forgot, what gland type are you using? Are you even glanding the cable off, or using wood blocks, earth starp and connection? Details my son, b*llsh*t is everywhere, facts are rare. Facts keep you alive, b*llsh*t kills. I make no apology to be so to the point, happy to help. But if you cany give detail you could end up injuring another or even wrse, you geting injured or even ....You are adding safety to a system, personnel and equipment. How can you get remedial facts if you dont know what you are doing or what you have existing. Done, Do it right First Time!!!

Not necessary as long as the armour cross section has the sufficient short time withstand current rating and is earthed properly.

Wrong!

...however, it is necessary if it is required by the end Client's electrical specifications, whoever "we" might be. Those documents cannot be seen from here.

Well dont worry to put your glasses on, I put mine on and I still could not see the documents. (I did see the naked lady next door though).

It has been my experience and also a code standard, that armor on cabling may not be used as an earth or common ground, as it would then be considered a conductor in the system. Use a separate cable, sized appropriately to handle the current and resulting temperature rise of a ground fault or short.That said, armor may be used as an RF shield if connected to earth on one end only, very handy if a VFD is used to control a motor in the circuit.

The armour cannot be used as a RF shield as it does not have the qualities or properties to perform that task. further to your statement I have installed many VSD's WITHOUT armoured cable

And to clarify to one and all, a separate earth conductor means a core within the cable itself and that core is dedicated for the function of earthing and NOT another single core cable OUTSIDE the cable you need earth protection for.

In many large power cables 50mm csa and above the cable could be 4 or 5 core. 4 core= 3phase plus earth, 5 core= 3phase, neutral and earth. These cores are either numbered or colour coded and the earth core depending on the electrical code of the country, could contain green plus another colour.

Since the OP did not specify the cable type, we are all making assumptions.

Look up IEEE 1580 Type P or Type E, Type E is purpose built for VFDs, each major conductor is individually shielded, and the metal armor is also a shield with 88% covering.

Most newer VFDs operate in the the 3-30 KhZ range and higher, which is well into the RF, and should be shielded to prevent harmonics on other system cabling, and standing wave problems on its own cabling.

If the OP was referring to common off the shelf, single phase triplex direct burial armored cable cable? They do not normally come with a 4th grounding lay, and it must be layed separately, you can order a quad lay cable but it would be special order from most cable suppliers.

I'm not sure from where you hail.. but in the UK and other parts of the world you run a 4 core cable.

With regards to your added suggestion of RF shielding from harmonics (which is another add-on from yourself) I would suggest that as the Op only asked about earthing.. why did you then add the totally un-related subject of RF shielding for VSD's?

Can we not stick to the question posed by the OP, and stop added un-related comments and suggestions?

Your idea is sound, but toatlly untrue in this case and that is on all accounts. Sorry to let you know this. The screen is for draining purposes, not RF or VFD sheidling. 4 Cores are common as dirt, ABC (triplex) comes with a catentry wire which goes to earth and it comes with 4 conductors. I wonder where you are or where you have worked, as I really wonder about comments on this site and just how systems are operating out there. I have to wonder. The time has come the Walrus said.......

SWA cable is proven to be a good earthing method for several years.

The gold rule for that is to follow a rigorous procedure to do this work. The armour is not only a mechanical protection. The cable armour shall be earthed at both ends of any interconnected equipment, the armour wire whichever be galvanized steel or aluminum, the ampacity should be able to withstand 1 sec. fault to earth current ( find it in cable cataloge)

A good practice to do a cable glanded should be done at least as follow:

• Select the proper gland size
• Select the gland material according to the area to be installed
• remove the cable sheath
• clean-up the armour wire to get a good contact
• insert the ring brace to fasten the armour
• Interconnect the ring brase by mean of conductor to the motor earth bolt
• Insert a gland shroud or any wrab element to isolate the motor-gland union from external corrosive ambient.
• Use an earth loop tester to measurement the right impedance value to permit the CB or fuses clean the fault under short circuit to earth.

The additional earth conductor is not required always in SWA cable when a good work is done

Bye

"The additional earth conductor is not required always in SWA cable when a good work is done"

Wrong!

If statements are supported by "quotes" from rules,regulations,standards it would be better appreciated.

See other posts. "There are none so blind as those who will not see". "The truth can only be found if you look for it."

I want to know why is it wrong, please explain yourself, I had beem working for years in a chemical plant and it work perfectly, all CB trip and fuses blow out.

The additional conductor is require in unarmoured cable as far as I know

Waiting for your explanation to know something else

bye

Take a cable theory course. They are expensive. I will tell you this, the subject is very debatable, but standrad practise is Gland all SWA to earth. Short run cables earth one end only, long cable runs earth both ends. SWA IS mechanical protection BUT, it IS electrical protection as well. Proof, disconnect the SWA on a 1kV cable, both ends, hit the live cable with a pick, or JCB, to a core. If you survive, let me know how you feel when you get out of hospital.

Disconnect the copper tapes on a 11kV un-armoured, XLPE cable, from earth, repeat the process with the pick or JCB, let me know when you are out of hospital.

In the USA it is different, a pole falls over, the line stays live, they have a different earthing system. So, in sensible countries, the SWA is glanded to earth, even in petrol-chemical companies and explosive manufacturing environments. The SWA comes in contact with a live core, the earth fault relay trips out making the system safe, no or little arcing, no high amperage, no high temperatures and no injuries. Saves cable, saves you, saves expense, Clever folks we are and we teach for free. And your un-armoured cables are normally in ducts or on cable racks, not direct buried. NB on a 220KV cable the insulated sheath can have a standing voltage of 150V, hence transpositioning of cores and link boxes every 1km or near enough that distance. And the armour is down to earth, usually a corrugated sheath of aluminium. Do a cable theory course. Or employ me!

nice one.. you beat me to it!! GA

"I want to know why is it wrong, please explain yourself,".. I don't have to explain myself to anyone

"I had beem working for years in a chemical plant and it work perfectly, all CB trip and fuses blow out." If what you state is truthful then Sir, you have been damn lucky so far, as I know from personal experience chemical plants and the like are hard on glands of any type.

"The additional conductor is require in unarmoured cable as far as I know". Yep as far as you know.. so there is a gap in your education and you ability to read the posts in the chain. I strongly suggest that you expand your horizons, find a good technical book of electrical standards, IEEE or the UK electrical codes and give your an education.

By the way Mr brich, the electrical design, project, erection and guarantee of chemical plant that I mentioned were made by an English company from your country ( Simon Carves LTD) based in cables BS 5464, BS 6262 and IEC 502 and supervised by LOYS Insurance. Also CMP Gland manufacturer also from England made special FLP glands for hazardous area, maybe I had been lucky But any way I'll will take your recommend for future, just to be more careful in may next project revisions

You started off so bold with your opening statement. Now you have faded. I suggest you update on IEC standards quickly, IEC 60840, 2011 to start with and all the associated standards recorded inside. If these are the standards you use. Be smart, check with your supervisor, buyers, design engineer, etc, Find out what standards they work to. Read there standards sitting on the bookshelf, then get the updated ones to read. And honestly, if you come here with well verse questions, offering proper details, (voltage, cable types, country, etc.), I am sure we will be happy to assist you, but guess work, none of us can help you with. Every system in every country is different and has it quirks. Happy reading. Happy learning.