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Zs readings over limits
Former Community Member
Doing an EICR in a block of flats and quite a few of the lighting circuits have excessive Zs readings. All the circuits are on 60898 C10's without RCD protection with readings in the late 2 early 3 ohm range (max permitted 2.19). I know test result fails are generally a code 2 but these are LED panel downlighters with mostly class 2 drivers connected via choc boxes above the suspended ceiling so nothing really accessible. They would all comply with a C6 btw. Just wondered if you'd C2 this resulting in an unsatisfactory EICR
It seems to me that this circuit is non-compliant, but is relatively low risk as parts connected to the CPC can not be readily touched.
To rectify, several approaches are possible.
Fit a smaller MCB*, fine WRT to load current but possibility of tripping on inrush current.
Fit a faster acting MCB*, also chance of tripping on inrush currents.
Rewire in larger cable to reduce the loop impedance, arguably the best solution but expensive and disruptive.
Install an additional CPC, also costly and disruptive.
Connect the CPC of this circuit with that of another nearby circuit. Complicates future testing, and could be rendered ineffective by future changes.
Fit an RCD, preferably not a 30ma type due to risk nuisance trips. A 100 ma type would give quick acting protection with the reported loop impedance.
*Be aware that a lower rated or faster acting MCB might have been the original design, and that the presently fitted device MIGHT have been retrofitted when the LED lights tripped the original OCPD.
It seems to me that this circuit is non-compliant, but is relatively low risk as parts connected to the CPC can not be readily touched.
To rectify, several approaches are possible.
Fit a smaller MCB*, fine WRT to load current but possibility of tripping on inrush current.
Fit a faster acting MCB*, also chance of tripping on inrush currents.
Rewire in larger cable to reduce the loop impedance, arguably the best solution but expensive and disruptive.
Install an additional CPC, also costly and disruptive.
Connect the CPC of this circuit with that of another nearby circuit. Complicates future testing, and could be rendered ineffective by future changes.
Fit an RCD, preferably not a 30ma type due to risk nuisance trips. A 100 ma type would give quick acting protection with the reported loop impedance.
*Be aware that a lower rated or faster acting MCB might have been the original design, and that the presently fitted device MIGHT have been retrofitted when the LED lights tripped the original OCPD.
