Max Zdb TNS system help

[Bradley6969]

TNS system Ze is 0.3 ohms all good now sub mains is fed from this but I’m getting 3.15 ohms still should be under 0.8 ohms?
Thanks

 

[davesparks]

The Zs of the submain needs to be less than the maximum for its protective device, the same as any other circuit.

 

[westward10]

How long is this submain, conductor csa and type of protective device.

 

[Wilko]

Hi - May need some more info to be helpful.
But if you started with Ze of 0.3 on TNS and added some decent sized cable for submains and are now getting over 3 Ohms earth loop impedance, then I'm guessing you've either got a poor connection or a very very long sub mains.

 

[Bradley6969]

400amp 60269-2 can’t find it max zz anywhere hahaha

 

[Wilko]

Sorry, do you mean you've got a 400A fuse on Ze of 0.3 ?

 

[westward10]

If you have a 400A 60947-2 device then the cable is somewhat large. You have a Zs of 3.15 ohm, now unless this is of considerable length you must see something is not correct.

 

[westward10]

Thread closed see link for similar thread.
Caravan site readings on TT system - https://www.electriciansforums.co.uk/threads/caravan-site-readings-on-tt-system.172970/