HeyBub wrote:
Just Joshin wrote:

I had a few computers die on me, they were old, but taught me a
lession. I had to tackle my voltage spikes a few ways.

1. Surge surpressor in the panel. Medium cost.
2. Ensuring proper panel grounding. Few bucks.
3. Point of use surge surpressors. low cost.

With all three, I've not had a killed another computer or electronic
applicance. So, what can you get from my experience? Tackle each
problem head on, don't be cheap and try and get a secondary benifit
from another safty device. Good luck.


#3 is not necessarily "low-cost." The el-cheapo surge protectors use MOVs to
clamp the spikes. Problem is, these MOVs, which act like fuses in reverse,
only work once (or a few times). After that, you're unprotected with no
indication of the possible peril. Better is a moderately-priced surge
protector, ~$50, that has sopisticated electronics instead of MOVs.

Look for the ones that guarantee to protect attached loads.


According to the IEEE guide, "the vast majority (90%) of both
hard-wired and plug-in protectors use MOVs to perform the
voltage-limiting function. In most AC protectors, they are the only
significant voltage limiters."

MOVs are intrinsically all voltage clamps - when the voltage rises over
a characteristic voltage the MOV conducts to try to keep the voltage at
that level. They are like back-to–back Zenier diodes. MOVs don’t
protect by absorbing energy, but they absorb energy in the process of
protecting.

A single MOV will have an energy (Joule) rating, say 5000J for argument.
If the MOV takes a single hit of 5000J the voltage at which it conducts
will decrease by 10% and the MOV is considered to be at end of life. (It
will still work, but as it takes more hits the voltage at which it
starts to conduct will progressively get lower.) As the energy hit per
event goes down, the cumulative total energy the MOV can dissipate goes up.
At 5000J per hit the cumulative dissipation is 5000J
At 1500J per hit the cumulative dissipation might be 13,000J.
At 200J per hit the cumulative dissipation might be 200,000J.
Buying a suppressor with a high energy rating gives a much longer life
than would be anticipated. With a very high rating, it is not likely a
plug-in suppressor will ever ‘wear out’. I believe that is why some of
these high energy rating suppressors have a lifetime guarantee on the
suppressor. They are also likely to have a guarantee for protected
loads. Any decently rated plug-in suppressor will work far more than “a
few times”.

MOVs are likely to fail by the conduction voltage decreasing until the
MOV conducts on normal power and goes into thermal runaway. Since 1998
the UL standard has required MOVs to be disconnected when they overheat.
The IEEE guide spends quite a bit of space differentiating between
plug–in suppressors that connect the protected load across the MOV, so
it will be disconnected with the MOV - or connecting the protected load
so it stays live when MOVs are disconnected. In the first case, you will
certainly be aware of “possible peril”, and I would recommend it. Far as
I know all suppressors have indicator lights that indicate they are
functioning.

François Martzloff , who was the author of the NIST guide on surges,
says that overvoltage is the most frequent cause of failure of surge
protectors.

The IEEE guide cautions against comparing suppressors based on energy
rating because there is no standard its measurement. High energy
ratings, however, indicate long life. The IEEE guide gives
recommendations for surge current rating.

The 3 points of JustJoshing are the same as the IEEE guide. A 4th point
is a single point ground - where the entry protectors for cable,
phone, dish,... are near the power service panel and connect by short
wire to the earthing wire at the power panel. Not having a short
connection causes the problems discussed in another post.

--
bud--