TN-C-S System Max Zs for Final Circuit Protected By 30mA Type B 16A RCBO Electrical Advice

TN-C-S System Max Zs for Final Circuit Protected By 30mA Type B 16A RCBO Discussion ThreadTN-C-S System Max Zs for Final Circuit Protected By 30mA Type B 16A RCBO Electrical Advice

TN-C-S System Max Zs for Final Circuit Protected By 30mA Type B 16A RCBO

I have read a few articles stating that under BS7671, max permissible Zs earth loop impedance for above circuit is 1667 Ohms.

1667 ohm permissible Zs for above circuit protected by 30mA RCD would only seem to satisfy BS7671 clause 411.4.4 in regards to fault current. There is also a requirement to provide overcurrent protection i.e. MCB/RCBO. Table 41.3 details max Zs for the overcurrent characteristics of RCBO which is 1.37 Ohms for Type B 16A RCBO. A 1667 ohm Zs would seem to be non-compliant in regards to overcurrent characteristics of RCBO detailed in Table 41.3

Granted at best, Zs can only infer the impedance of line/neutral for overcurrent short circuit scenario . But never the less, this is the requirement of Table 41.3 for the overcurrent characteristics of an RCBO.

Interested in your thoughts on this.

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