What happens if the SWA cable is only connected to the SWA at one end for CPC/Earth at the gland?  I imagine no loop

Sergio Fernandez said:

What happens if the SWA cable is only connected to the SWA at one end for CPC/Earth at the gland?  I imagine no loop

Not sure what you mean by this?

If the armour is connected to PE, say, at the source end but not the remote end, then L-armour fault would occur via loop back through source PE?

If the armour is connected to PE at the remote and but not the source end, say TT system, then the loop is back through the TT earth electrode to the source (e.g. distributor's earth electrode, but in TN-C-S system, also through PEN conductor multiple earthing) - may require an RCD at the source end of the cable for ADS. In this case, the lowest earth fault loop might be known, but the maximum prospective earth fault current cannot always be determined with certainty (Guidance Note 6 tells us what to assume here in the case it's not known with certainty).

Steven Wills (Steve) said:

Amtech firstly calculates the Zs using the armour only

The fault might occur with damage to the cable itself (possibly being severed). I guess it depends, for your application, whether you think that ought to be taken into account?

Steve

Amtech has a drop down option for the cable CPC. The options are SWA armour only, Armour plus CPC, CPC only and then you have an option for integral or separate CPC. 

If you select armour plus CPC your Zs values should reduce and may be low enough.

When you have selected your option do a "Calculate" and then you will be able to see any errors in the design.

Hope this helps?

JP

Thanks John,

The armour and CPC are selected but am I correct in thinking that initially the Zs is calculated using the armour only? And if this level is too high it results in an error? Then Amtech recalculates using the addtional CPC in parallel with the armour to give a lower reading which is acceptable, but this only comes up as a note? So ultmately, there is an initial error that is listed but the note says that in fact the Zs for this cable is ok? So does this note cancel out the error?

Steve

I put my own cable data in to Amtech and then do a calculate. If I get errors on cables I will change the cable CSA, CPC CSA and adjust MCCB or ACB settings to correct any errors. I don't let Amtech calculate cable CSAs. I don't think Amtech calculates armour only if you have selected amour plus CPC and you have entered a CPC CSA.

JP