geoff said:
I do not understand what you are writing. First you write:
. . . then you write:
. . . so, which is it, does he believe that protection must use earthing or
does he think surges are stopped?
Both were right.
w believes the only effective way to protect against surges is earthing
- as in the post I responded to:
"Protection is about diverting surges into earth."
Because *plug-in* suppressors do not work primarily by earthing w
believes they must work by "stopping" or "absorbing" (which I agree
won't work). They don't. If w was not blinded by his religious belief
in earthing he could read in the IEEE guide that plug-in suppressors
work primarily by clamping the voltage on all wires (power and signal)
to the ground at the suppressor. The voltage going to the protected
equipment is safe for the protected equipment. (See the IEEE guide
starting pdf page 40.)
You are putting a whole lot of fluff into the basic idea that surpressors
and UPS' work by either clamping/absorbing/etc. (whatever you want to call
it) or by redirecting surges to ground.
The question is basic to understanding how plug-in suppressors work. It
is basic to understanding why w is wrong when he says plug-in
suppressors do nothing useful. And it is important in understanding how
to apply plug-in suppressors - particularly why phone and cable wires
that go to protected equipment have to go through the suppressor.
For mild surges that come from the power company, I'm sure both a good UPS
or surge protector can successfully clamp the voltage. In fact, on my UPS
software, it has a panel that asks for the voltage range. If the power goes
above or below that range, the UPS switches to the battery.
Switching to battery won't protect against surges - they are too fast (I
am not sure you are saying switching to battery will protect).
A UPS will probably protect against overvoltage (which is far longer
duration than a surge). (As my post said, overvoltage is more likely to
damage suppressors than surges.)
My reservation about UPSs is that, in general, the surge protection
ratings are lower than what is readily available in plug-in suppressors.
And any suppressor (in the US) should be listed under UL1449 (surge
suppressors) - a lot of UPSs aren't.
For a lightning strike, unless one has some expensive equipment, then you
are SOL.
Everything I have read indicates that a plug-in suppressor with high
ratings, wired correctly, is very likely to protect from a very near
lightning strike (but not a direct strike to the house, which requires
lightning rods). That is why some manufacturers can have warrantees on
protected equipment.
(In part repeating from my last post
François Martzloff was the NIST guru on surges. He wrote the NIST guide
as well as many technical papers. One of the technical papers looked at
the energy that reaches a plug-in suppressor (with no service panel
surge suppressor). The maximum energy dissipated was 35 Joules. In 13 of
15 cases it was 1 Joule or less. That was with power line surges from
2,000 to 10,000A (the maximum that has any reasonable probability of
occurring).
35J is well within the rating of plug-in suppressors. And 10,000A is
well within the rating of service panel suppressors.
If a large surge enters on the power service, when the voltage from
busbars to the enclosure reaches about 6,000V (US) there is arc-over.
After the arc is established the voltage is hundreds of volts. Since the
enclosure is connected to neutral and “ground” (US) that limits the
voltage that equipment in the building “sees”. Since the enclosure is
also connected to the earthing electrode most of the incoming surge
energy is dumped to earth. This is one reason the energy reaching a
plug-in suppressor is so low.
The other reason is the impedance of the branch circuit. A surge is, by
definition, a very short event. That means it is a relatively high
frequency event. So the inductance of the wire is more important than
the resistance. The impedance of the branch circuit wiring limits the
current to the plug-in suppressor, which limits the energy that reaches
the suppressor.
The 10,000A maximum likely power line surge came from another Martzloff
paper which had a 100,000A lightning strike (only 5% are stronger) to
the utility pole behind a house. A stronger surge is very unlikely -
average calculated probability of a stronger surge is one in 8,000 years.
Add a service panel suppressor and protection is better.
Have short wires connecting phone and cable entry protectors to the
earthing wire at the power service and you increase protection.
