main bonding

[Andy78]

And the regulation you think this falls foul of is ...... or maybe you dont!

Maybe I don't. It got replaced for a continuous cable all the same.

 

[capa666]

Does the building have a steel structure if so bond to that, as long as the steel is bonded back at the MET which it should be anyway!

The building is structural steel, sheeting rails and cladding,,, I noticed it on a job I looked at last week, the origin isn't that far away were there is a suitable MET and section board, however the contractor has decided to bond steel, water and gas from a sub DB, the sub main is a 16mm SWA cable, using the SWA as the earth.. It interested me as I have never seen that done before, I can see that they have done it because the incoming supplies were close to the DB but I was unsure wether this is acceptable??

 

[Engineer54]

The building is structural steel, sheeting rails and cladding,,, I noticed it on a job I looked at last week, the origin isn't that far away were there is a suitable MET and section board, however the contractor has decided to bond steel, water and gas from a sub DB, the sub main is a 16mm SWA cable, using the SWA as the earth.. It interested me as I have never seen that done before, I can see that they have done it because the incoming supplies were close to the DB but I was unsure wether this is acceptable??

Using the 16mm SWA as a main earth bonding conductor is NOT acceptable, it will not have an appropriate copper equivalent CSA. The steel wire armouring is fine for use as a CPC but not where protective main earth bonding requirements are also to be met!!

 

[skydog23]

I can't believe someone put that connector block on upside down.

It looks absolutely awful lol.

 

[IQ Electrical]

Tony mc hit the nail on the head, once that structural steel is bonded, you've got a rather large main protective bonding conductor to 'tap off' to bond other services.

 

[capa666]

Using the 16mm SWA as a main earth bonding conductor is NOT acceptable, it will not have an appropriate copper equivalent CSA. The steel wire armouring is fine for use as a CPC but not where protective main earth bonding requirements are also to be met!!

Thanks engineer 54, I thought as much, seeing things like this makes you think somebody knows something more than you. I didn't want to point it out as incorrect and look stupid if there was a way of doing it that way. Is there a calculation to use to determine the size it must be?? Let's say the sub main was a 150mm SWA cable, would it then be sufficient ? I would always say it has to come from the origin, but surely there will be some kind of calculation that would determine if it was safe. Thanks again, Iam just trying to understand it a bit further as you do

 

[Richard Burns]

Generally it is not recommended to use the armouring of SWA as a bonding conductor, especially where the supply is TNCS as there can be currents circulating through the bonding due to the design of the PME system that may have adverse effects on the current carrying capacity of the cable as a whole.

The comparative calculation for steel versus copper as a conductor is that the steel must have a cross sectional area of 8.5 times that of the copper because the steel is less conductive.
This would mean that where a 16mm² copper bonding conductor is in use then a steel conductor would need to be 136mm² to afford the same protection.

16mm² SWA armour has a CSA of 45mm² which is approximately equivalent to 5mm² in copper so unsuitable for any bonding conductor, even is it were an acceptable use of the armour.