Use of SWA armour as protective bonding conductor?

[SW1970]

Thanks - it's a completely detached garage. It's PVC SWA. Spin - can I use the armour and CPC combined in some way?

 

[Deleted member 26818]

I'm not 100% sure when the requirement for 10mm² bonding came into force.
Definately there in 2004.
It may have been when ESQCR 2002 was introduced.

 

[Deleted member 26818]

Thanks - it's a completely detached garage. It's PVC SWA. Spin - can I use the armour and CPC combined in some way?

Not ideal, but the CSA of the armour and the CPC would meet the requirement for 10mm².
You'd have to make a note of it on the Certificate.
Something along the lines of 'utilising the SWA armour and the 6mm² CPC to meet the requirements of 544.1.1 to provide a 10mm² CSA Protective Bonding Conductor'.

 

[SW1970]

So do you mean:

- combine the 6mm2 third core with the equiv 4mm2 armour to give a 10mm2 protective bonding conductor
- the other 2 cores remain as L and N
- terminate SWA properly at boths ends and extend to MET (main house) and EMT (garage)
- in the garage, the equipotential bonding from the services should run to the EMT (are in fact already in place)

This is what I had in mind with the original post (yes, really), but wasn't sure if it's a goer or not. Not sure how the distribution circuit CPC is catered for then?

 

[Guest123]

can I use the armour and CPC combined in some way?

I don't believe this arrangement would be permissible as the conductor needs to be large enough to carry the fault current on it's own. This is why when installing an additional earthing conductor along with a 4 core SWA for example, we don't size one to use in addition to the armour but size it to carry out the function itself.

 

[Deleted member 26818]

Yes that's exactly what I'm suggesting.
To my mind, a conductor can be both a bonding and a CPC at the same time.
Just waiting for someone to disagree and state that the 10mm² has to be a single condutor, or that both conductors have to have the same CSA or something.

 

[Guest123]

Yes that's exactly what I'm suggesting.
To my mind, a conductor can be both a bonding and a CPC at the same time.
Just waiting for someone to disagree and state that the 10mm² has to be a single condutor, or that both conductors have to have the same CSA or something.

Lets have your reasoning then.

 

[SW1970]

Thinking that the protective bonding conductor may have to carry large fault current in the event of failed incoming neutral or neutral of the distribution circuit. In this case, the distribution circuit is protected by RCBO so it should trip anyway?

 

[Deleted member 26818]

Lets have your reasoning then.

I was assuming that the 6mm² CPC was adequately sized.
With PME, the CSA is chosen so the conductor can withstand diverted neutral currents for long periods of time, rather than earth fault currents for short periods of time.

 

[netblindpaul]

There has been research and testing provided to the "industry" that goes along with the idea that the fault current will be shared acceptably by an internal core & the SWA, & / or an external cpc, the internal core & the SWA.
So you can do any of the above.
Also if you check GN1 you will get armour csa's for compliance with table 54.7, from this you should be able to assess your suitability.

Also you can use the adiabatic to size bonding conductors.