w_tom wrote:
On Mar 28, 2:00 pm, clifto wrote:
So you get a good surge from nearby lightning, and the three wires on your
computer's power plug all go to a common-mode voltage plus or minus line
voltage. But your ground is bad, so you have a common-mode voltage about
4,000 volts above earth ground.
And you're touching the computer, or you have a telephone line plugged
into it, or an Ethernet wire from another location, or somehow have
one of many other possible and even likely scenarios in which the other
end of the person/line is grounded fairly well. 4,000 volts on one end
and ground on the other... bring the weenies and marshmallows.
Not all the protection is meant for the device plugged into the strip.
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, all those wires have to run through the surge
suppressor for protection. The voltage on all wires connected through
the suppressor (power, phone, cable TV, ...) is clamped to the common
ground at the suppressor and the voltages are held to a value that is
safe to the connected devices. This is described in both guides.
A voltage from the protected equipment to other points is possible, but
the guides do not mention it as a practical hazard, and I have not seen
it mentioned in any of the other literature I have read. And part of the
premise is that the ground wire is bad. Incidentally, at about 6,000
volts there is arc-over in panels or receptacles which limits the
maximum voltage appearing between hot, neutral and ground wires.
Say you have a service panel surge protector with the service earthed
only by a ground rod. There is a surge on the power lines that produces
a relatively modest 1,000A earth current. The impedance to earth is a
very good 10 ohms. The voltage from the panel to 'absolute' earth is
10,000 Volts. In general about 70% of the voltage drop from a ground rod
to 'absolute' earth is in the first 3 feet. From the house power and
ground wires to earth beyond 3 feet from the ground rod is 7,000 Volts.
With a single point ground most of that voltage will also appear on
phone and CATV wires. The differential can appear in the house and can
be the same problem.
Meanwhile, Bud's own citation shows a TV being destroyed by more
voltage - 8000 volts - because of the power strip protector. Bud
claims that is proof of an IEEE recommendation when IEEE makes
recommendations elsewhere - in Standards. Multiple IEEE Standards
define one thing for protection - earthing.
You have to be really stupid to say the IEEE would release a guide to
the general public that is not consistent with IEEE standards. And the
IEEE guide, pdf page 4, makes it absolutely clear that the IEEE guide
has been peer-reviewed and represents the views of the IEEE. But w_ must
deny the obvious to protect his religious belief in earthing.
As the IEEE guide makes clear, plug-in suppressors work by CLAMPING the
voltage on all wires to the common ground at the suppressor, not earthing.
Bud provided:
http://www.mikeholt.com/files/PDF/Li...ion_May051.pdf
Go to Adobe page 42 (paper page 33) to see Figure 8. TV2 is
destroyed by 8000 volts because earthing was defective and because
protector was too far from earthing.
8000 volts on a TV - that is called effective protection? Never
was.
A plug-in surge suppressor protects what is plugged in to it. The text
clearly says "To protect TV2, a second multiport protector located at
TV2 is required." In this particular example, a service panel surge
suppressor would not protect either TV because the surge comes in on the
CATV wire and there is not a single point ground for incoming power and
CATV wires - there would be 10,000V from CATV lead to power wires at
both TVs. You can't get a single point ground from the CATV entry ground
block to the power service when the CATV entry point is distant from the
power service. (Service panel surge suppressors are, however, a good idea.)
w_'s objections to plug-in surge suppressors are because they violate
his religious belief in earthing. But both the IEEE and NIST guides say
plug-in suppressors are effective.
--
bud--