Maximum Zs Value Exceeded Discussion ThreadMaximum Zs Value Exceeded Electrical Advice
Hi
I have recently done some testing on an installation. A submain is fed from a B50 mcb and has a zs of 1.10ohms. The maximum for this is 0.87. The cable supplying the submain is a 25mm 2 core swa with the armourings used as the cpc and is roughly a 70m run. Both glands and earth leads have been checked and are okay.
Would it be viable to fit a 300ma rcd to protect this circuit as the disconnection time cannot be achieved. The problem I have is the building supplied by this has two large heaters and a number of vacuums and there is an earth leakage of around 150ma.
Each circuit in the submain has individual 30ma protection.
Upgrading the cable/running a separate earth alongside the swa would not be possible due to the nature of site.
Maximum Zs Value Exceeded for the original thread on Electricians Forums
Hi
I have recently done some testing on an installation. A submain is fed from a B50 mcb and has a zs of 1.10ohms. The maximum for this is 0.87. The cable supplying the submain is a 25mm 2 core swa with the armourings used as the cpc and is roughly a 70m run. Both glands and earth leads have been checked and are okay.
Would it be viable to fit a 300ma rcd to protect this circuit as the disconnection time cannot be achieved. The problem I have is the building supplied by this has two large heaters and a number of vacuums and there is an earth leakage of around 150ma.
Each circuit in the submain has individual 30ma protection.
Upgrading the cable/running a separate earth alongside the swa would not be possible due to the nature of site.
Maximum Zs Value Exceeded for the original thread on Electricians Forums
