w_tom wrote:
Again, to keep this in perspective. A protector is not protection.
Building earthing is the protection. So that every wire in every
cable gets connected to protection, a 'whole house' protector is
installed. That protection is enhanced by expanding or improving an
earthing system.
Excellent information on surges and surge is available in an IEEE guide at:
http://omegaps.com/Lightning%20Guide...ion_May051.pdf
Or a similar NIST guide at:
http://www.nist.gov/public_affairs/p.../surgesfnl.pdf
The IEEE guide is more technical (and better).
The IEEE guide explains that plug-in surge suppressors work primarily by
clamping the voltage on all wires (signal and power) to the common
ground at the suppressor, not earthing. The guide explains that earthing
occurs elsewhere.
If a power strip is connected elsewhere on the same branch circuit,
then protector is providing to everything on that circuit as if those
appliances were plugged directly into that power strip protector.
Nope. If a plug-in suppressor is significantly downstream from your
“appliance”, there is far too much voltage drop between the suppressor
and the “appliance”. Protection other than connecting through the
suppressor is a dumb idea.
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I haven’t looked at many specs, but UPSs are likely to go to battery
mode on overvoltage. A *few* plug-in surge suppressors are designed to
disconnect on overvoltage. Other than that I agree that surge
suppressors provide no overvoltage protection. A major author on surges
said "In fact, the major cause of TVSS [surge suppressor] failures is a
temporary overvoltage, rather than an unusually large surge."
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Regarding earthing as protection for an open neutral:
Any protection relies on an alternate neutral path from the building
service neutral to the neutral at the transformer, usually via the earth.
Looking at only the resistance from the building service
neutral-to-earth - a very good (low) resistance is 5 ohms. The neutral
carries only the imbalance between the hot legs. If the imbalance is a
very small 10 amps, the voltage drop from neutral–to-earth is 50 volts.
That means that one leg can be 70 volts and the other leg can be 170
volts with a small 10A imbalance. And the resistance of the earth and
resistance from earth-to-transformer is not included.
(The voltage actually is also determined by load resistance on each leg.
And as the voltage shifts, the current will increase on the higher
voltage side and go down on the lower voltage side lowering the current
imbalance.)
This probably works better in an urban area with metal water supply
pipe. The return path can be neutral–to-water service, water
pipe-to-another building supplied by the transformer, other building
water pipe-to-neutral, and other building neutral-to-transformer. This
is an all metal path.
On May 21, 12:22 pm, NoOne N Particular wrote:
I wish I had a whole house surge protector last week.
Whole house is a good idea. But make sure phone, cable,... service entry
protectors are adjacent to the power service, and the protectors connect
with a short wire to the earth conductor at the power service. This is
called a "single point ground". You want to keep the ground reference
for all systems at the same potential.
--
bud--