When the Measured Zs is greater than the Maximum permissible Zs as set out in Reg 411.1, the colour of the measured Zs will turn red to warn the user that the values are above the requirements:
Is the System Type TN-S or TN-C-S?
If yes, the values are what they are and should be displayed as failing (unless an RCD protects the whole board or individual RCBO's protect each circuit).
Is the System Type TT?
If Yes, and there is RCD protection for the whole system (either by means of an RCD at the Origin / DB / or individual RCBO's) - you can either turn the Zs warnings off by following the instructions below.
To turn off this feature, set the option to OFF and click Update as shown in the image below:.
Or - a more advanced option exists to include more information including the Main switch type and mA rating, or whether RCBO's should be used for individual circuits.
Is the Main switch an RCD?
If Yes, then you can set the Zs preferences option as shown in the images below.
Any Max Zs value will now display the correct value as shown below:
If you have already selected a circuit, you will need to refresh it to adopt the new Max Zs value - change the overcurrent device rating to something else, then set it to the one you want. (The lesson here is to set the Zs preferences first!!)
Is there a mixture of circuit breakers and RCBO's in the DB?.
If Yes, then you can set the Zs preferences option as shown in the images below.
Max Zs values will now be appropriate for the device chosen, if values for the 60898 exceed the maximum, the value will still turn red. This may be preferable when carrying out EICR's to demonstrate the installation as it is.
