Electrical distribution substations often have (wired) telephones which use super high-voltage isolation transformers between the phone and the phone line. This is to protect the user of the phone in the event that there is some kind of fault at the substation which produces a large difference between the local ground where the user is standing and the phone line. This could be either contact between a power line and the phone line OR it could be a large ground potential difference between the ground reference of the phone line and the local ground where the user is standing. The transformer (at least the one I saw) is about the size of a large desktop PC so it dwarfs the phone itself! Sean On Fri, Jul 20, 2012 at 10:14 AM, Harold Hallikainen wrote: > > Protecting equipment from lightning is quite a challenge. The telephone > industry has really done an amazing job. I was once talking with an > engineer at a radio transmitter site in Florida. During the conversation, > I heard a buzzing sound, then the phone dropped. A minute later he came > back and said he'd been thrown across the room by a shock from the phone. > The connection stayed up the whole time. > > Impressive stuff! > > > Harold > > > -- > FCC Rules Updated Daily at http://www.hallikainen.com - Advertising > opportunities available! > Not sent from an iPhone. > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .