w_tom said:
Hardly. w_tom verses the sales promoter who will not admit he
promotes these protectors.
..
Poor w_ thinks that anyone who opposes his outlandish ideas (which are
not in this post) is a sales promoter. Totally false.
The best information on surges and surge protection I have seen is at:
<
http://www.mikeholt.com/files/PDF/LightningGuide_FINALpublishedversion_May051.pdf>
- "How to protect your house and its contents from lightning: IEEE guide
for surge protection of equipment connected to AC power and
communication circuits" published by the IEEE in 2005 (the IEEE is the
dominant organization of electrical and electronic engineers in the US).
And also:
<
http://www.nist.gov/public_affairs/practiceguides/surgesfnl.pdf>
- "NIST recommended practice guide: Surges Happen!: how to protect the
appliances in your home" published by the US National Institute of
Standards and Technology in 2001
The IEEE guide is aimed at those with some technical background. The
NIST guide is aimed at the unwashed masses.
..
UL approval
requires total number of joules to be listed.
..
Nope. UL does require the current and clamp voltage to be listed and
defines how to measure them.
The IEEE guide cautions against comparing Joule ratings because there is
no standard for measurement. So some manufacturers play games to inflate
their Joule ratings. Because of that some other manufacturers have
stopped supplying Joule ratings - including SquareD.
It is too bad, because Joule rating, like w_ says, is an indicator of
suppressor life. But current ratings go up with Joule ratings.
Service panel and plug–in suppressors do not protect by absorbing surge
energy, but absorb energy in the process of protecting. Joule ratings
are for the energy that is absorbed by the MOV. This is not the energy
in the surge.
As Rahul said Joules are the product of clamp voltage, current through
the protective device, and surge duration. (But the voltage and current
change during the event.) The "8/20uS" figure indicates the measurement
was made with a pulse of 8 microseconds rise time and 20 microseconds
duration. This is one of the standard test pulses and is similar to a
surge produced by lightning. It is fairly reliable to compare Joule
ratings if the test method (8/20) is stated.
The common practice, as Paul said, is to add the Joule ratings of
protective devices in the suppressor but this should also be indicated
by the manufacturer (and often isn‘t). Protective devices for power
wires are almost always MOVs.
Stated Joule ratings are for a single event - one surge that puts the
MOV at its defined end of life (but still functional). If the energy
hits are much smaller, the cumulative energy rating is much higher. For
example a MOV might have a (single event) rating of 1,000J. If the
individual hits are 14J the cumulative energy rating might be 13,000J.
High ratings give a much longer life than you might expect.
Francois Martzloff was the NIST guru on surges and wrote the NIST guide.
He has written "In fact, the major cause of [surge suppressor] failures
is a temporary overvoltage, rather than an unusually large surge."
Temporary overvoltage is long duration - seconds to hours?days.
..
285 joules is high enough to claim surge protection but so close to
zero as to be almost no surge protection.
..
I would rather see higher ratings. But 285J is not as "close to zero" as
w_ believes.
Martzloff wrote a technical paper (available on the internet) which
looked at a MOV at the end of a branch circuit, with no service panel
surge suppressor, with surges on incoming power lines of 2,000 to
10,000A and with branch circuits of 30 feet and longer. The probability
of a surge over 10,000A is near zero. The maximum energy dissipated in
the MOV was 35 Joules. In 13 of 15 cases it was 1 Joule or less.
I recently bought a plug-in suppressor that had ratings of 30,000A and
590J per MOV for each of the 3 MOVs. The 30,000A rating is not real in
that it is not possible to get 30,000A on a branch circuit (short of
lightning hitting the house). But 30,000A goes with the high Joule ratings.
--------------
According to NIST guide, US insurance information indicates equipment
most frequently damaged by lightning is
computers with a modem connection
TVs, VCRs and similar equipment (presumably with cable TV
connections).
All can be damaged by high voltages between power and signal wires.
Note that all interconnected equipment needs to be connected to the same
plug-in suppressor, or interconnecting wires need to go through the
suppressor. External connections, like phone, also need to go through
the suppressor. Connecting all wiring through the suppressor prevents
damaging voltages between power and signal wires. These multiport
suppressors are described in both guides.
