UK Amtech/Trimble - Excessive Earth Loop Impedance on SWA cables

[Steve W]

Hi All,

I'm new to Amtech/Trimble and I've been asked to review a model.

I'm looking at circuits that are SWA cables using the armour and an internal conductor as the CPC. There are various earth loop impedance errors listed where the Zs at the load end is too high, but what I can tell, Amtech firstly calculates the Zs using the armour only, and if this is too high it sees it as an error, but it then recalculates using the internal CPC in parallel with the armour to reduce the Zs to an acceptable value. There is a note listed referencing the same cable stating this, so I'm I correct in thinking that even though Amtech says this is an error but it actually isn't because of the note explaining the second calculation? Basically, does the note cancel out the error? It seems a bit ambiguous to me......

 

[Vortigern]

Sounds like it would be sage to get out your resistivity tables and do a manual check to make sure Zs meets BS7671 requirements. There is listing for armour in regs. As to the software aspect, I would look to the designer of it tech support and question that. for due diligence.

 

[timhoward]

The old saying comes to mind:
"to err is human, but to really foul things up requires a computer"

 

[plugsandsparks]

Definitely a call to Trimble on that one. At least if it gets one calculation correct, as mentioned above you can double check it against a manual calculation, then hopefully further calcs will be good....

 

[Steve W]

The old saying comes to mind:
"to err is human, but to really foul things up requires a computer"

It's the same with any system, if you put poo in, you get poo out!