We have undertaken circuit calculations that utilise Eaton MEM (MEMShield 3) devices. The calculation completes successfully and indicates the Zs values pass.We note that regulation 411.4.7 allows the calculation of Zs to satisfy the disconnection requirement and that this is the Hevacomp calculation method.The circuits have subsequently been tested on site by the contractor and have been noted that the values exceed those deemed to comply within BS7671 Table 41.3 We have provided the calculated values as reassurance however the contractor (to satisfy himself) has referred the issue to the NICEIC.The NICEIC response is as follows:“For the circuits that are not RCD protected if Eaton are able to confirm that their devices have a higher allowed Zs value and they still trip within the required time, thus making the currently failed circuits compliant, their max Zs values can be inputted to the test sheets instead of the ones from BS7671 and should result in the circuit passing.”We have requested published value of Zs from Eaton, which they have provided – but these are the same values as listed in BS7671.The question therefore is where have you sourced your Eaton Zs values? If we can receive this it will give the required credibility to the calculation results to be used within the completion certificate.Regards,
Hi Stuart,
We have been reviewing this in light of your request. Hevacomp calculates impedance in order to arrive at a fault current. That fault current is used with the time current curve of the device to ascertain the disconnect time. That disconnect time is checked against Regulation 411 to gauge pass or fail. All manufacturer data is checked an verified by the manufacturer before it is published. At present we do not hold Max Zs values in the manufacturers data but this is something we will review for future releases as an alternate to our current method.
Shane Regan | Principle Building Performance Support Engineer
Can I have a response please
Can Bentley please provide the response to the wider forum please.
I have recently attended a training course and the IET and NICEIC are of the opinion that the Zs calculation 411.4.4 should not exceed the values indicated in table 41.3 where the manufacturer data is the same as table 41.3. All Schneider and Eaton values for MCB's are provided in accordance with table 41.3.
Duncan Brown