Low pressure inert gas devices were the original surge
protectors. Like most shunt mode protector devices, they
remain as an open circuit until a transient voltage becomes
too high. Then like MOVs, they become short circuits to shunt
that transient to earth.

As noted previously, these principles of protection were
well understood and routinely installed in the 1930s. Back
then, a surge protector was typically a low pressure, inert
gas discharge tube (GDT) similar to an NE-2 neon glow lamp
(often still found inside lighted switches). In fact, some
radios used NE-2 on the antenna to protect RF amplifier
transistors.

Unfortunately Gas Discharge Tubes (GDTs) degrade quickly
with each use. Anode would vaporize into the gas, causing
threshold voltage to rise with each use. IOW like MOVs, they
degraded; but even faster.

By the 1970s, MOVs (or equivalent) were replacing GDTs.
Most every home had something equivalent provided free by the
telco:
http://www.inwap.com/inwap/chez/Phoneline.jpg

This Western Electric device was different from MOVs in
that, like GDTs, they were low capacitance devices. Two
cylinder cartridges called 'the carbons' were underneath
those hex bolts heads and could be replaced.

Today, telcos have long since obsoleted the carbons with a
semiconductor device. Both GDTs and 'the carbons' would
degrade without the human knowledge. Semiconductors either
work properly everytime or become short circuits. Either they
work or report their failure by shorting out the phone line.
Therefore GDTs have been obsoleted twice over.

For AC electric, a semiconductor type of 'whole house'
protector is available - albeit more expensive. The best
'whole house' (AC electric) protector for the buck uses MOVs
since destructive surges are so infrequent and MOVs (properly
sized) have such long life expectancy.

GDTs, in the meantime, are still used in special
applications such as commercial radio facilities. But even
electric utilities today use MOVs for substation protection.

GDTs, MOVs, or semiconductor protectors - all are only as
effective as the central earth ground. That essential
earthing principle, demonstrated by Franklin in 1752 and
widely installed in the 1930s, has not changed. No what what
the technology, a surge protector was only as effective as its
earth ground.

Barry OGrady wrote:
What about gas arrestors?

-Barry