After a great deal of searching for information, I still can't find a simple answer to the question of whether, and how, one should surge protect a DSL line.

Given that ADSL modems/routers are quite expensive, replacing one or more due to a lightning strike etc seems like a way to spend a lot of money, and I can definitely recall times when I've had unprotected modems fail just after a major storm.

From my searching I've gleaned three pieces of information (some related to the UK):

1) BT fit a surge protector in the master socket, but it's entirely differential mode across the twisted pairs (lightning surges usually present themselves as common mode as I understand it).

2) DSL is a high frequency signal and so any protector must be of very low capacitance to avoid loss of what is already probably a poor signal in most areas that suffer from lightning issues.

3) Any surge protector worthy of the name needs a proper earth to dump the surge to ground.

Is this accurate? What are other people's experience and/or advice on the subject? Has anyone ever come across a decent DSL surge protector that doesn't degrade signal, and has a chance of protecting sensitive comms equipment?

I've struggled to find any at all that are designed to deal with a high frequency signal. Presumably they exist - what are BT and telcos using?

Thanks in advance for any advice.

Furse www.furse.com supply a book 'A guide to BS 62305:2006 Protection against Lightning'. Someone in the organisation should be able to help.
Ian Darney

3) Any surge protector worthy of the name needs a proper earth to dump the surge to ground

Absolutely - all a surge arrestor does is divert the energy to earth via a path that doesn't include your product - as long as the surge is running down the telephone line.

Trying to protect yourself against the rare event of a nearby groundstrike is unlikely to be economical.