Thanks for both answers.
My power system is similar to the US. It is 480v, centre tapped Neutral (180 degrees phase shift).
I do have a transformer of known type (one supplied by Robin for a Solar HW diverter). Except for the Power factor, all working well.
I might even get another unit to monitor the house. Get the first working properly first tho.
I calibrated the 240v off the Solar Edge inverter. Power readings seem OK. I will wire the other V monitoring transformer in the next few days.
Thanks, Doug