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Cross sectional area of a protective conductors

MS01
Can someone give me a some advice on if we have a earth electrode system made up of the structural rebar when using the adiabatic equation to size of the bonding conductor comes out at 300mm. MY questions is does each bond need to be this size or can it be made up via a series of smaller bonds that are equal or exceed the 300mm requirement? My opinion is each bond needs to be this size to deal with the fault current as the direction it will flow is unknown. What are peoples thoughts? I cannot see anything in the regs on this.

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  • Former Community Member
    0 Former Community Member
    I think you need to draw the line diagram, and then look for those parts of the installation that carry earth fault current.


    Typically, both your transformers are closed into the switchboard and would have to be in parallel to achieve the fault level you quote. Presuming you can identify the N-E bond as either at the transformer, or more credibly at the switchboard, you should see that by far the largest proportion of fault current will return along that conductor in an earth fault.


    That conductor is referenced to earth via connections to the electrode - the resistance of which sets how much fault current can flow from bonding to rebar and back to the source point.


    Assuming all of your cabling design is "normal" and has adequately sized CPC's, then the bonding cannot see a fault current of 100/1.73 kA


    Regards


    OMS
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  • Former Community Member
    0 Former Community Member
    I think you need to draw the line diagram, and then look for those parts of the installation that carry earth fault current.


    Typically, both your transformers are closed into the switchboard and would have to be in parallel to achieve the fault level you quote. Presuming you can identify the N-E bond as either at the transformer, or more credibly at the switchboard, you should see that by far the largest proportion of fault current will return along that conductor in an earth fault.


    That conductor is referenced to earth via connections to the electrode - the resistance of which sets how much fault current can flow from bonding to rebar and back to the source point.


    Assuming all of your cabling design is "normal" and has adequately sized CPC's, then the bonding cannot see a fault current of 100/1.73 kA


    Regards


    OMS
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