Lightning seeks a conductive path to earth. A most common source of
lightning strikes is to AC utility wires. Incoming on AC mains, into
house, and out to earth ground via transformer.
Transformer provides galvanic isolation. But if that surge is too
large, then galvanic isolation will be overwhelmed. Transformer
primary (120 volt) and secondary (12 volt) conduct the surge to earth.
Do you think a power strip protector will stop what three miles of
sky could not? That is what another here has recommended. Real world
protection is about earthing that surge before it even enters a house.
Same one protector that is sufficiently sized to remain functional
after each lightning strike. Same one protector that also protects
everything inside a building.
The best information I have seen on surge protection is at
http://www.mikeholt.com/files/PDF/LightningGuide_FINALpublishedversion_May051.pdf
- w_tom provided the link to this guide
- the title is "How to protect your house and its contents from
lightning: IEEE guide for surge protection of equipment connected to AC
power and communication circuits"
- it was published by the IEEE in 2005
- the IEEE is the dominant organization of electrical and electronic
engineers in the US
A second guide is
http://www.nist.gov/public_affairs/practiceguides/surgesfnl.pdf
- this is the "NIST recommended practice guide: Surges Happen!: how to
protect the appliances in your home"
- it is published by the National Institute of Standards and
Technology, the US government agency formerly called the National
Bureau of Standards
- it was published in 2001
Both guides were intended for wide distribution to the general public
to explain surges and how to protect against them. The IEEE guide was
targeted at people who have some (not much - should be easy for anyone
here) technical background.
Both say plug-in surge suppressors are effective.
For complicated equipment, all interconnected devices, like a computer
and printer, need to connect to the same surge protector. If a device,
like a computer, has external connections like phone or LAN, all those
wires have to run through the surge suppressor for protection. This
type of suppressor is called a surge reference equalizer (SRE) by the
IEEE (also described by the NIST). The idea is that all wires connected
to the device (power, phone, CATV, LAN, ...) are clamped to a common
ground at the SRE. The voltage on the wires passing through the SRE are
held to a voltage safe to the connected device. The primary action is
clamping, not filtering or earthing.