Thanks Cracker

We have a similar complaint after finishing a MV reticulation job.We have an Eskom 11Kv incoming along with a Genset feeding a step up transformer to 11Kv
The Eskom and Genset 11Kv feeds onto an Automatic transfer switch which then feeds the ring with 4 x 200Kva minisubs fitted with Class 1&2 combined surge arrestors
If Eskom falls away the genset automatically takes over the 11Kv feed.
We are switching the MV 1 000 m away from the minisub and I would not expect any type of switching spike to have an effect on the LT supply

The electrical contractor doing the LT works is having a problem with a Dali interface "blowing " when we switch between supplies.We have checked our side and don't find anything but when I looked at his panel I see all sorts of basic mistakes just waiting to go wrong including his class 2 surge arrestors being wired with 2,5sqmm wire - I am no expert in surge arrestors but it just seems wrong when you are 10m away from a 200Kva minisub with a 125Amp feeder CB.He does appear to have a 20Amp CB protecting the surge arrestors which to me is also incorrect.