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Hope this is in the right place...

Our firm recently tested a 20 year old office installation and one of the flagged items is the lack of earth rings on the swa cables feeding the under floor tracks. The cables are glanded into the metal D/B. Earth for the sockets is provided by a third core in the armoured so the glanding provides the bond for the armouring only.

Are earth rings required?
 
Not really I would say providing locknuts are tight and the paint beneath them scratched off, Ideallythey would of used serrated washers. At worst, if there was good continuity from the armour you could give it a c3,
If the paint is scratched off and the locknuts tight, then NO code, think conduit and MI.
 
P

Plonker 3

Personally I would say as long as one end of each SWA is earthed then it is fine just to guarantee that the armourings are earthed, so fitting "Banjo's" should be done weather it is a C2 or C3 would depend on several factors.

As Somerset says if they are tightly terminated and no paint causing a continuity problem then C3 otherwise C2.
 
I don't think there is any specific requirement for banjos to be fitted in bs7671, many large jobs specify serrated washers, no banjos, Therefore I would not code unless there was an earth continuity problem. Nobody ever banjos conduit or MI.
 
P

Plonker 3

I don't think there is any specific requirement for banjos to be fitted in bs7671, many large jobs specify serrated washers, no banjos, Therefore I would not code unless there was an earth continuity problem. Nobody ever banjos conduit or MI.
MI is rarely used these days unfortunately.

On tray, conduit etc it should all be bonded and again continuity too the MET should be proved.

Maybe I was a little harsh on my initial assessment, but in certain circumstances it should be i.e. buried underground on walls etc even if the armor isn't used as a C.P.C.
 
I think the key is the soundness of the connection, really I would like to see either a banjo or a serrated washer. I would much rather see a scratchy washer and paint removed then the usual 'banjo on top of paint!' that is pretty common!
 
As you point out, the earthing is done via a cable core, so the swa glanding is to earth the steel only. Have to agree with what the others have said, not ideal but as long as there is a good connection then no problem.
 
  • Thread Starter Thread Starter
  • #8
Thanks for confirming my thoughts. There are times when its easy to talk yourself into doing more than necessary just cos you overthink the job...
Once again, thanks for the replies.
 
im a bit confused about the inital question?
i have to ask, as you have pointed out the earth return path is supplied by the third core?

so are the earthing rings only providing protection should the steel armour become live? (obviously and absence of earthing banjos)
in which case as a precaution i would check as above, that serated rings are used. and provide a suitable sized fly lead from the steel box.
this would insure a fault free earth path.
and should be easily changeable from the existing installation.
 
G

Guest55

Although not strictly required i'd consider it good practice to banjo & earth lead at least at the DB end of the swa.
But at worst its only a code 3 defect.
 
have to agree with the above. ive allways, used banjo rings regardless. as a precaution. be sure to sand/file back the paint on the boxes aswell. for a good connection.
 
MI is rarely used these days unfortunately.

On tray,( conduit etc it should all be bonded and again continuity too the MET should be proved.

Maybe I was a little harsh on my initial assessment, but in certain circumstances it should be i.e. buried underground on walls etc even if the armor isn't used as a C.P.C.
Surely Tray only requires bonding if its extraneous and earthing only if it falls under exposed conuctive part which it generally is not
 
P

Plonker 3

Well seeing as most tray work will be carrying cables and could become live, I would bond all exposed electrical containment together, otherwise you wouldn't need to bother getting couplers tight on it along with trunking or bother threading galv conduit properly would you?
 
There is only a requirment if it falls into the 2 i have listed if not then does not reqire to be bonded. look at gn8 earthing and bonding it states this too. Earthing stuff that does not require it can infact make it more dangerous.
 
P

Plonker 3

So you are happy leaving metal work that is carrying cables not to be bonded back to the MET?

Explain how that is dangerous and not a safety connection then please?
 
So you are happy leaving metal work that is carrying cables not to be bonded back to the MET?

Explain how that is dangerous and not a safety connection then please?
Dillb mate

Yes i am happy leaving metal work that is neither extraneous or exposed conductive parts unbonded/earthed. just like when i have put up double insulated metal fittings, with BS and the double square markings i have not decided to earth them to be on the safe side

heres why
Exposed-conductive-part.Conductive part of equipment which can be touched and which is not normallylive, but which can become live under fault conditions.
Extraneous-conductive-part. Aconductive part liable to introduce a potential, generally Earth potential, andnot forming part of the electrical installation
A cable tray or a cable basketwhere used as a support and cable management system has to be considered in thecontext of earthing and bonding. In other words, are such systems, whereconsisting of metal and plastic-coated metal, exposed-conductive-parts orextraneous-conductive-parts and consequently do they require earthing orbonding?
Addressing, first, the questionof earthing and whether the cable tray or basket should be earthed, electricalequipment such as cables mounted on a metallic support system will normally beequivalent to either a Class I construction (for example copper sheathed,mineral insulated cables without an overall PVC covering) or a Class IIequivalent construction (for example PVC insulated and sheathed cable).
Exposed-conductive-parts ofcables, such as the copper sheath of a mineral insulated cable, are required tobe connected to the MET of the installation by a CPC designed to conduct earthfault currents. The cable tray or basket which the mineral insulated cable isattached to, or may be in contact with, is not itself anexposed-conductive-part and therefore it does not require earthing. To do sowould only serve to distribute further any touch voltage resulting from anearth fault on an item of equipment to which the cable is connected.
A cable complying with theappropriate standard having a non-metallic sheath or a non- metallic enclosureis deemed to provide satisfactory protection against both direct and indirectcontact, as does an item of Class II equipment (Regulation 471-09-04 refers).Class II equipment is constructed such that any insulation fault in the cablecannot result in a fault current flowing into any conductive parts with whichthe equipment may be in contact. Hence, the metal cable tray or basket need notbe earthed

 
P

Plonker 3

Where is that text quoted from?

At least give the author the credit.
 
Gn8

well worth the read, will answer all earthing questions:wink5:
 
P

Plonker 3

Well at least post the whole article and not just the parts you want too.
A cable tray or a cable basket where used as a support and cable management system has to be considered in the context of earthing and bonding. In other words, are such systems where consisting of metal and plastic-coated metal, exposed-conductive-parts or extraneous-conductive-parts and consequently do they require earthing or bonding?

Addressing first, the question of earthing and whether the cable tray or basket should be earthed, electrical equipment such as cables mounted on a metallic support system will normally be equivalent either a Class l construction (for example copper sheathed, mineral insulated cables without an overall PVC covering) or a Class ll equivalent construction (for example PVC insulated and sheathed cable).

Exposed-conductive-parts of cables, such as the copper sheath of a mineral insulated cable are required to be connected to the MET of the installation by a CPC designed to conduct earth fault currents. The cable tray or basket which the mineral insulated cable is attached to, or may be in contact with, is not itself an exposed-conductive-part and therefore it does not require earthing. To do so would only serve to distribute further any touch voltage resulting from an earth fault on an item of equipment to which the cable is connected.

A cable complying with the appropriate standard having a non-metallic sheath or a non-metallic enclosure is deemed to provide satisfactory protection against both direct and indirect contact, as does an item of Class ll equipment (Regulation 471-09-04 refers). Class ll equipment is constructed such that any insulation fault in the cable cannot result in a fault current flowing into any conductive parts with which the equipment may be in contact. Hence, the cable tray or basket need not be earthed.

Generally, the conductive parts of a metal cable tray or basket system need not be puropsely earthed. Some conductive parts of a metal cable support system may be earthed, however, by virtue of fortuitous contact with exposed-conductive-parts.

Should the cable tray or basket be equipotentially bonded? Unless the metal cable support system introduces a potential that does not already exist in the location which the system is installed, it will not meet the definition of an extraneous-conductive-part. In normal circumstances therefore there is no need to arrange for the conductive parts of the support system to be connected to either a main bonding conductor or any supplementary bonding conductor.

However, should the cable tray be installed in such a manner that it is lekely to introduce a potential from outside the location, thereby meeting the definition of an extraneous-conductive-part, then main equipotential bonding will be required (Regulatiuon 413-02-02 refers). For example, consider a run of cable tray carrying services into a particular building. The cable tray may be in contact with the earth potential ouside a building and upon entering into the building would be likely to introduce the earth potential into that building. In such a case the tray would warrant the defintion of an extraneous-conductive-part and consequently main equipotenial bonding would be required.

Where, for example, the installation designer has selected a cable tray for use as a protective conductor, which is permitted under Regulation 543-02-02(vi) where it is described as an electrically continous support systerm for conductors, the cable tray would be required to meet the requirements for a protective conductor given in Regulation 543-02-04 and would need to be connected with earth.
 
However, should the cable tray be installed in such a manner that it is lekely to introduce a potential from outside the location, thereby meeting the definition of an extraneous-conductive-part, then main equipotential bonding will be required (Regulatiuon 413-02-02 refers). For example, consider a run of cable tray carrying services into a particular building. The cable tray may be in contact with the earth potential ouside a building and upon entering into the building would be likely to introduce the earth potential into that building. In such a case the tray would warrant the defintion of an extraneous-conductive-part and consequently main equipotenial bonding would be required.

as i said if it was classed as an extraneous conductive part it would require bonding. if it is not then no bonding required
 
Dillb mate

Yes i am happy leaving metal work that is neither extraneous or exposed conductive parts unbonded/earthed. just like when i have put up double insulated metal fittings, with BS and the double square markings i have not decided to earth them to be on the safe side

heres why
Exposed-conductive-part.Conductive part of equipment which can be touched and which is not normallylive, but which can become live under fault conditions.
Extraneous-conductive-part. Aconductive part liable to introduce a potential, generally Earth potential, andnot forming part of the electrical installation
A cable tray or a cable basketwhere used as a support and cable management system has to be considered in thecontext of earthing and bonding. In other words, are such systems, whereconsisting of metal and plastic-coated metal, exposed-conductive-parts orextraneous-conductive-parts and consequently do they require earthing orbonding?
Addressing, first, the questionof earthing and whether the cable tray or basket should be earthed, electricalequipment such as cables mounted on a metallic support system will normally beequivalent to either a Class I construction (for example copper sheathed,mineral insulated cables without an overall PVC covering) or a Class IIequivalent construction (for example PVC insulated and sheathed cable).
Exposed-conductive-parts ofcables, such as the copper sheath of a mineral insulated cable, are required tobe connected to the MET of the installation by a CPC designed to conduct earthfault currents. The cable tray or basket which the mineral insulated cable isattached to, or may be in contact with, is not itself anexposed-conductive-part and therefore it does not require earthing. To do sowould only serve to distribute further any touch voltage resulting from anearth fault on an item of equipment to which the cable is connected.
A cable complying with theappropriate standard having a non-metallic sheath or a non- metallic enclosureis deemed to provide satisfactory protection against both direct and indirectcontact, as does an item of Class II equipment (Regulation 471-09-04 refers).Class II equipment is constructed such that any insulation fault in the cablecannot result in a fault current flowing into any conductive parts with whichthe equipment may be in contact. Hence, the metal cable tray or basket need notbe earthed

as above
 
I always thought that tray should be bonded, I Remember doing my AM2 and having to bond the tray, basket, especially with T+E could become live with snagged cable etc, however it is usually connected to earth via the main frame of the building anyways.

With regards to the article above, it mentions tray being used as a protective conductor, I have always thoght this was not allowed?
 
I always thought that tray should be bonded, I Remember doing my AM2 and having to bond the tray, basket, especially with T+E could become live with snagged cable etc, however it is usually connected to earth via the main frame of the building anyways.

With regards to the article above, it mentions tray being used as a protective conductor, I have always thoght this was not allowed?
When i sat my fica we got told to supplementry bond the tray too, were told dont ask questions just do it
 
When i sat my fica we got told to supplementry bond the tray too, were told dont ask questions just do it
Your dead right, best not to rock the boat when being tested! I don't know the right or wrong of this one im afraid, your presenting me with logical reasons but something just tells me it should be bonded!
 
Your dead right, best not to rock the boat when being tested! I don't know the right or wrong of this one im afraid, your presenting me with logical reasons but something just tells me it should be bonded!
we were told dont question it dont leave it or you will loose points
At the end of the say its up to us as installers to decide . I just read as much as i can fit in, to try an gain knowledge as to why to do it or why not. some people still say bond sinks or metallic furniture in kitchens ect ect cos its what they have done for donkeys and they will continue to do so i suppose
 
G

Guest55

... some people still say bond sinks or metallic furniture in kitchens ect ect cos its what they have done for donkeys and they will continue to do so i suppose
Then those people dont understand why they are doing something , or what constitutes an extraneous conductive part.
 
I can see a tray load of SWA's or MICC wouldnt need bonding unless it met the definitions of an ECP, however if it was a basket full of twins I would be tempted to, however most of the trays/baskets I have seen pick up very good connections to earth through purlings/ RSJ's etc. Whether they then need bonding is doubtful I suppose, as they are reliably connected to earth.
I have been on jobs as part of the 'earthing squad' though and have had to bond acroos every piece of racking and framework with 70mm links though, however different systems are in place on these jobs and they are often not to BS7671
 
D

Deleted member 26818

Getting back to the banjos.
If the manufacturer's instructions indicate that banjos should be used, then they become a requirement of the Reguations.
 
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