Testing of generators

[sparks will fly]

After some advice and opinions please.
An installation I have just tested also has generator back up. To what extent would you go with the testing when the installation is on genny supply. Would you re test every circuit that the generator supplies, or be happy that if the zs of the generator is adequate at the mains changeover, then all circuits should be ok.

 

[Plonker 3]

Section 551 of the BGB covers this and will tell you all you need to know.