Re: low voltage
In my experience, my phone continues to work with data and voice when on the station platform with trains passing or seated on the train directly under these cables. I've not tried the compass there, next time I don't know when in the future, I will try it.
Aged about 10 or so we had a rail line passing the end of the school playing fields and on frosty morning we were guaranteed a show of fizzy blue arcs as the trains passed the spots where the cables are suspended.