Using Armour of SWA as a Bonding Conductor.

[rattlehead85]

Could any of you helpful lot on here give me a clear answer on the following.
Can the armouring of a 70'c swa cable be used as a compliant protective bonding conductor?

Looking at the actual size figures of armouring for 70'c swa cables and applying the equation 5.5 from page 55 of GN8 it works out that none of the armour sizes comply for use as a protective bonding conductor. Am i interpreting this correctly or am i missing something.
I have never used armouring as a bonding conductor previously but have come across a situation on an EICR where the armouring of a 2 core 25mm (60mm armour size)has been employed as both the earthing conductor and protective bonding. I fully understand using the tables in BGB that the armour complies as an earthing conductor but i need advice on the protective bonding part.

 

[Pete999]

Not sure what mate using the armoring as a bonding conductor. can you explain what you are trying to achieve

 

[silverfox1]

See post 10 in this thread. http://www.electriciansforums.co.uk...al-regulations/87080-outbuilding-submain.html

 

[rattlehead85]

Not sure what mate using the armoring as a bonding conductor. can you explain what you are trying to achieve

I have a situation where an EICR is being carried out on a flat. The supply is fed from a TN-C-S communal intake using a 2 core 25mm. Inside the flat we have 3 10mm copper bonding cables serving gas, water and an extraneous metal soil pipe in the kitchen al terminated back at the C.U. Therefore the armouring is being used as a combined earthing and protective bonding conductor back to the head in the communal hall. I am trying to confirm, clarify if this armouring is compliant for how it is being employed.

 

[telectrix]

i think he's referring to the min. size for a bonding conductor ( 10mm in the case of PME ) is larger than the equivalent steel. in other words, the csa of the armour would need to be approx. 85sq.mm, to comply.

 

[rattlehead85]

See post 10 in this thread. http://www.electriciansforums.co.uk...al-regulations/87080-outbuilding-submain.html

Thanks silverfox that has cleared that one up for me.
I actually did have it correct and have attributed a c2 departure as armour inadequately sized for use as a protective bonding conductor, but started to doubt my interpretation of the BGB/GN8.
So looking at the actual 70'c armour sizes none of the cables are suitable to use as a bonding conductor.

 

[Pete999]

i think he's referring to the min. size for a bonding conductor ( 10mm in the case of PME ) is larger than the equivalent steel. in other words, the csa of the armour would need to be approx. 85sq.mm, to comply.

Tel I may be completely in the wrong direction, the OP says he has a 25mm 2cSWA and 10mm main bonding conductors, think I have that bit right. Looking at table 5 SWA @ 70deg the min csa of a cu bonding conductor is 16mm and the steel equivalent is 60mm so this installation is wrong on 2 counts, and why has the original installation got a 10mm to the extraneous metal waste pipe, probably a daft question as the OP is not the installer he is just doing an EICR.

 

[Simlec]

I would say the SWA has been fused down for the flat (say 63a) and the 10mm bonds are within the flat itself back to the flats CU.

 

[rattlehead85]

Tel I may be completely in the wrong direction, the OP says he has a 25mm 2cSWA and 10mm main bonding conductors, think I have that bit right. Looking at table 5 SWA @ 70deg the min csa of a cu bonding conductor is 16mm and the steel equivalent is 60mm so this installation is wrong on 2 counts, and why has the original installation got a 10mm to the extraneous metal waste pipe, probably a daft question as the OP is not the installer he is just doing an EICR.

To clarify. The bonding needs to be 10mm sized against the neutral of the installation which is 25mm.
The extraneous soil pipe in the kitchen is simultaneously reachable with a worktop socket. This pipe was confirmed as being extraneous and therefore requires main protective bonding which was found to be present during the test.

 

[rattlehead85]

I would say the SWA has been fused down for the flat (say 63a) and the 10mm bonds are within the flat itself back to the flats CU.

Yes this is exactly how it is simlec.

 

[rattlehead85]

Would this same equation be applied if the means of combined earthing and bonding back to the intake was via a steel conduit?.

 

[Engineer54]

I have a situation where an EICR is being carried out on a flat. The supply is fed from a TN-C-S communal intake using a 2 core 25mm. Inside the flat we have 3 10mm copper bonding cables serving gas, water and an extraneous metal soil pipe in the kitchen al terminated back at the C.U. Therefore the armouring is being used as a combined earthing and protective bonding conductor back to the head in the communal hall. I am trying to confirm, clarify if this armouring is compliant for how it is being employed.

In a Single word, the answer is NO!! You will need to provide a suitably sized separate main bonding conductor from the service head (MET) to the CU/DB (EMT)...