On Sep 30, 11:32 am, N8N wrote:
My understanding is that there are generally three MOVs in a typical
AC-only surge protector, H-N, N-G, H-G. If any of those MOVs fail
they generally fail shorted rather than open, directly either shorting
a current-carrying conductor to ground or else shorting hot to
neutral. This causes an internal fuse or circuit breaker to open,
completely disconnecting the load from the line. Thus this *does*
protect the load from a surge, unless the overvoltage is such that it
can actually cross the gap in the fuse/breaker.
Errors upon errors. But you are correct. Those are popular myths
promoted by the electrically naive (ie salty@dog) and protector sales
promoters (bud).
First, if any MOV vaporizes, then it has violated Absolute Maximum
Parameters listed at the top of every datasheet from every MOV
manufacturer. Only acceptable MOV failure mode is to degrade.
Degrade means its voltage changes 10% AND the MOV is not burned,
shorted, open, or vaporized. Because the naive observe grossly
undersized protectors burn, then the naive *know* vaporization, et al
is a normal failure mode.
Scary pictures show what can happen when MOVs fail by shorting,
vaporizing, etc:
http://www.hanford.gov/rl/?page=556&parent=554
http://www.westwhitelandfire.com/Art...Protectors.pdf
http://www.ddxg.net/old/surge_protectors.htm
http://www.zerosurge.com/HTML/movs.html
http://tinyurl.com/3x73ol
http://www3.cw56.com/news/articles/local/BO63312/
Most every fire department has seen these totally unacceptable
events. Only the naïve say this is acceptable.
Read any MOV manufacturer datasheet. Voltage, current, or energy
necessary to create a shorted or vaporized MOV is well beyond where
chart lines end ... because that failure mode is unacceptable and a
threat to human safety.
Second, this MOV failure mode does not disconnect any load. To
disconnect a grossly undersized protector even faster, its thermal
fuse is tiny. A thermal fuse only disconnects MOVs. And that surge
may be even smaller. An even smaller surge will blow that thermal fuse
so that MOVs do not vaporize. Again, it gets the naive to promote
that protector.
Third, you have assumed an open fuse will stop what three miles of
sky cannot. Read the numbers on any fuse. Typically rated for ‘x’
amperes and 250 volts. Why 250 volts? Because electricity at higher
voltage will continue to flow through that blown fuse. Assume your
assumption is correct: that a fuse blows to disconnect the appliance.
Suddenly that fuse rated at only 250 volts will stop 6000 volts? Of
course not. The blowing fuse maintains a plasma path that continues
to conduct that surge until the surge terminates. Fuses never open to
disconnect a surge.
Surges are current mode events. Voltage will rise as high as
necessary to conduct or arc through whatever tries to stop it. Any
protector that would stop or disconnect from a surge is a myth.
Protection is always about diverting surges as even Bud's citations
bluntly state.
Assumed is that a fuse will blow fast enough. It could not stop
voltage. It also cannot open fast enough. Surge current flows
simultaneously through everything in that path to earth - including
the appliance. A fuse takes tens or hundreds of milliseconds to
blow. But a surge has already done damage and terminated in
microseconds. 300 consecutive surges could pass through that fuse
before a fuse (or circuit breaker) even thinks about blowing. Junk
science does not provide numbers. This post says why AND includes
numbers.
Summary so far: Why is a surge never blocked - especially by a
fuse? a) Surge flows through everything long before a fuse sees that
surge. b) 250 volt fuse cannot stop surges. c) Fuses take maybe 1000
times too long to open. d) Fuse only tries to protect MOVs; does not
disconnect the appliance. Now move on to other myths that promote
plug-in protectors.
Fourth: what does every Bud citation and every citation from me
state? From the NIST on page 17 (Adobe page 19):
A very important point to keep in mind is that your
surge protector will work by diverting the surges to
ground. The best surge protection in the world can
be useless if grounding is not done properly.
A surge is not stopped or absorbed by any protector. NIST states
exactly where that surge energy must be diverted to: earth ground.
Previously discussed was wire impedance. An effective protector makes
a 'less than 10 foot' connection to earth ground. Why? Too much
impedance (not resistance) means the surge finds earth ground,
instead, inside the building. What happens when a plug-in protector
is adjacent to the appliance (obviously something like 120 ohms
impedance from the breaker box)? The plug-in protector with all but
no earthing connection diverts the surge, 8000 volts destructively, to
earth via an adjacent TV. That is Bud's other citation: Page 42
Figure 8.
We engineers have seen this repeatedly when tracing surge damage.
The plug-in protector provides the surge even with more potentially
destructive paths to earth via appliances.
How to identify the ineffective protector? 1) It has no dedicated
earthing wire. 2) Manufacturer will not even discuss earthing.
Industry benchmarks in surge protection such as Polyphaser discuss
earthing extensively:
http://www.polyphaser.com/technical_notes.aspx
Fifth: what do MOVs H-G, H-N, and N-G do? MOVs do not stop or
absorb surges. The surge seeking earth is simply distributed
(diverted, shunted, bonded, connected) from one wire to all wires.
Now that surge has even more paths to destructively find earth
ground. One classic example is Page 42 Figure 8. A surge exceeding
8000 volts puts 8000 volts destructively inside that TV. What did the
plug-in protector do? Exactly what its manufacturer specs claim.
Protector did nothing but give the surge a path to earth via the
adjacent TV.
N8N has accurately described what so many believe (assume). How
many errors and outright myths promote plug-in protectors? At least
nine have been identified in this post. MOVs must degrade - must
never vaporize or open. Every MOV manufacturer says this. Nothing
stops or blocks surges - especially fuses. Fuses voltage is woefully
too low; response time is 1000 times too long. Thermal fuse is for MOV
protection - never protects or disconnects the load. If a thermal
fuse - the emergency backup protection circuit - does not open fast
enough, then scary pictures can result. Every responsible source
describes what provides protection. Not a protector. Protection is
earth ground. Surge energy can never be blocked or absorbed. Surge
energy must be dissipated harmlessly in earth.
What does the effective protector have? Typically the 'less than 10
feet', no sharp bends, etc. connection to earth.
A $3 power strip with some ten cent parts sells for $25 or $150.
Why do APC, Tripplite, Belkin, Monster Cable, etc not sell 'whole
house' protectors? Profit margin on plug-in protectors is obscene.
Only responsible companies sell 'whole house' protectors. Unlike
APC, et al, responsible companies have names that everyone should
recognize: Siemens, Intermatic, Cutler-Hammer, Square D, Keison,
Leviton, GE, and others.
Learn what the professionals do. Your telco's switching computer is
connected by overhead wires everywhere in town. It can suffer
typically 100 surges during every thunderstorm. How often have you
been without phone service for five days as they replace that
computer? Never. Telcos use a 'whole house' protector on every
incoming wire of every cable - connected as close to earth ground as
is practicable. Separation between protector and electronics
increases protection – contrary to what plug-in promoters claim.
Telco wants their protector up to 50 meters separated from electronics
to increase protection. Telco does not waste money on plug-in
protectors. The telco has same surge problems as a homeowner - just
more of them. So that telephone service works just fine during every
thunderstorm, telcos use better earthing, 'whole house' protectors,
and no plug-in protectors. Telco does not install protectors that
would open or vaporize to provide protection. And telcos have been
doing this (not using plug-in protectors) for the past 100+ years.
Reality cannot be explained in a sound byte. Plug-in protectors (ie
what you were told) is sound byte logic (junk science reasoning).
However, a sound byte can summarize the above: No earth ground means
no effective protection. Surge energy must be dissipated where?
Harmlessly in earth ground. A protector is only as effective as its
earth ground.