Serendipity

Lightning took out the PSU, but not the device? Really? Or, you don't know yet, because you haven't sorted out the replacement PSU yet?

For some unexplained reason you seem to have strayed into my killfile! Turnpike is a bit too clever sometimes.

Telephones all working fine with the substitute PSU. E-Bay is posting me the proper replacement.

Where would the energy from a line surge go if shunted by some unknown protective device at the telephone input?

The secondary circuit will be isolated from mains. Probably feedback is via optical coupler

depends if it were the mains line or the phone line #

Where is w_tom?

Hmm.. Phone lines are overhead, LN underground from the transformer.

This is lighting we are talking about, the rule book goes out the window.

The current flow in the ground near a strike is very high and can produce serious voltages, enough to kill large quadropeds. Conductors are conductors, they don't mind which way the current flows, high local earth voltage and current could well flow "backwards" down the buried supply and/or supply earth back to the substation or PME points.

really high voltage is still overhead. A surge can happen if lightning strikes a 132kv line

The hot side of an SMPSU is rectified mains ~400VDC, and most components are right on that limit. make that 550V and kiss the unit good bye. If anything shorts there will be some kind of non user serviceable fuse to ensure it goes dead instead of catching fire. Part of the certification for wall warts (is supposed to) ensure that that voltage never gets through to user land. I.e. the mains is totally isolated.

Since the way these things work is high frequency chopping of the 400VDC and applying that to a ferrite transformer, that's where the main isolation happens - at that transformer.

From there on there are three ways of proceeding - either allow that voltage to be relatively unstable and have no feedback or use an optical circuit to feed back to the primary chopper, to vary the pulse width and hence effective input voltage to achieve regulation, or feed a separate low voltage stabiliser.

So my educated guess is that a mains surge took out the PSU, but the phones were fine as the phone line was not involved.

If you get a surge on the phone line it tends to take out anything connected to it, and these days that's usually the ADSL router. They shouldn't go, because they have isolation transformers, but the transients are so sharp I expect the edges get capacitively coupled. Had two netgears that went 'odd' after a thunderstorm

I've also had a PABX die.

That's all from line surge. Line strike is a bit worse. All sorts of random mayhem as the strike jumps to anything conductive. #

The router is OK. I have a stretch of 11kV overhead crossing the farm. 1/3rd mile T underground to the local transformer and then 400m underground back to us.

Engineering have been doing some switching locally but whether routine Summer maintenance or damage repair is unknown.

As you hint, lightning is curious stuff!

Cows having a good scratch on old wooden poles have been known to cause arcing between phases.

Not a lightning strike but a major underground cable failure. Amongst other things it took out the charger for my battery screw driver but not the device itself. Took out surge protection on 2 hot tubs, my CH timer and also TV aerial amplifier. Phone was OK though.