No. A voltmeter is high impedance. If you use a lamp then it would
That's the one! Thanks.
If it does not have the less than 10 foot earth ground
I seem to be getting several conflicting answers here.
Basicly, all I'd like to know is: can I trust the surge protector (or
"parasite eliminator" or something as the manufacturer calls it) in my
extension cord (or power strip or whatever) to protect my equipment? Does
it at least do *any* good, or can I just leave it out?
This discussion is getting somewhat big, so I'd like a definate answer
Surges are ideal current sources; not voltage sources.
Instead, plug-in protectors must avoid all discussion about
w_tom <w_tom1@hotmail.com> wrote in message news:<3F28370D.84617975@hotmail.com>...
The reason why a typical plug-in protector has no effective
earth ground connection (via green safety ground wire or white
neutral wire) is that wire has impedance. A 50 foot 20 amp
wire measuring 0.2 ohms resistance may also be 130 ohms
impedance to a surge current. Sufficient to safety ground 60
Hz power (20 amps times .02 ohms is less than 1 volt) but
insufficient to earth a surge (100 amps times 130 ohms is
13,000 volts).
No offence but you are throwing a lot of information that you got from
application notes. While the information is essentially correct, you
are misinterpreting most of it. If I am too far from ground that wire
impedance is making it ineffective as you say, then by the same token,
the surge that is travelling that same distance to the surge protector
on the phase will be attenuated by the same amount won't it? So if the
surge protector is one end of a 50ft wire and you surge the other end,
then by your calculation, it would drop 13KV. So unless the surge was
greater than 13KV, there would be no problem right?
"Hotdamn Paw fergit the Purtector! I'm a gonna steal me 50 ft of
wire."
Wire impedance is why the telco installs their 'whole house'
protectors where wires enter building directly on earth ground
AND prefer a 50 meter separation between protector and
switching computer. The impedance in 50 meter wire adds more
protection to the surge protection circuit. Their 'whole
house' protector has near zero impedance to earth ground and
maybe 100+ ohms impedance to $multimillion computer. If they
located surge protector next to computer, then that 100+ ohm
wire impedance back to earth ground would result in switching
computer damage.
My computer only costs about 800 bucks. Am I going to install
equipment and a ground worth a couple of thousand (plus installation),
to protect something that is worth less than that? Or am I going to
walk into Fry's and pick up a 25 buck spike supressor? A TELCO can
afford to do a lot of things. When the CEO of a TELCO wants to travel,
he flies in a Lear jet. Me..I take the bus.
Internal choke actually has a function different from what
many assume. Too many assume it is to filter the surge. Yes,
but not for reasons assumed. I believe Littelfuse
applications notes explain it best. That choke can slow a
rising edge of a large transient. By lengthening the surge, a
MOV is less likely to vaporize on a single massive surge.
Choke inductance is really not much of a filter. But it will
dampen the rising edge of a 100+ amp, single microsecond, type
transient. Dampen enough that the MOV has a better chance of
survival - not become a short circuit. Another way to
accomplish same is to simply install more MOVs - increase
joules.
Again this depends on the design. There are many tpes of protection
devices. Typically semiconductor based devices such as Diacs or Sidacs
have snubber circuits which function as you describe above. MOVs could
have them too but for an entirely different reason. However what you
are describing as "choke inductance" is different from the common-mode
choke which is a filter.
The reason why MOV's are paralleled is because the cost of the MOV
exponentially rises with its capacity to handle energy (The Joules you
keep talking about which you claim can determine my life expectancy
suppressor with 10 MOVs of smaller capacity than with one MOV with 10
times that capacity. The trick is to get them all to fire at the same
instance. If one fires before the others, then all the energy would
flow through that one device and destroy it. If you put an inductor
before all of them, it allows the gradual build up of energy and helps
in minimizing the above effect.
However if wire impedance back to earth ground approaches or
exceeds 100 ohms, then no effective earth ground exists
anyway. This is the problem with plug-in protection. It has
all but no earth ground due to wire impedance, too many wire
splices, many sharp bends, possibly inside conduit, bundled
with other non-earthing wire, etc. All mean the plug-in
protector does not have a prerequisite and effective
connection to central earth ground. Wire impedance is so
important to surge protection that Littelfuse even discusses
wire impedance of 2 inch leads on their MOVs. Even wire
length on MOVs affect impedance and testing numbers. Wire
impedance is why plug-in protectors have all but no earth
ground connection. Wire impedance is why the less than 10
foot connection is so important.
Hey man did you move your house to your Utility's Power Generation
station? They have the best ground. If you ask them nicely, them may
let you set up camp 2 inches away from it. No offence Tom. You are an
intelligent person reading something from some websites and then boom!
You wind up with some explanation that I find hard to read without
bursting into laughter. Yet you claim to have two EE degrees at some
other post. Anyway I will take you at your word. If you got EE then
you can follow this stuff.
http://www.itu.int/rec/recommendation.asp?type=folders&lang=e&parent=T-REC-K.11
The above is a link to an ITU-T recommendation entitled "Principles of
protection against overvoltages and overcurrents"
This and some of the other K series documents is what I refer to when
I design protection circuitry. (By the way if you register, you can
download 3 standards free)
Also don't forget to read NIST's recommendataions on Surge protection
http://www.nist.gov/public_affairs/practiceguides/surgesfnl.pdf
Another good and practical guide to surge protetction is your local
PG&E website.
Joules in a surge protector can determine life expectancy.
But quality of earth ground determines how effective the
'system' is during one surge. Superior earthing is why one of
my experiments so effectively protected an entire half of a
house using only one 70 joule MOV. Believe me. I was
completely amazed. Entire circuit from AC main to earth
ground in conductive soil was about 2 feet. Surge protector
made effective by earth ground including the short connection.
Primary function of a surge protector is to protect any humans. Its
secondary function is to protect the circuits downstream. If it can
protect itself while doing so, that's a bonus.
tube2ic wrote:
w_tom <w_tom1@hotmail.com> wrote in message news:<3F267D26.CEEC344D@hotmail.com>...
Now provide the inductance of that choke - the numbers.
Ironically, an electronic appliance must already have a
superior in-line choke filter. In other threads, some bought
cheap power supplies that did not have that required filter.
The resulting radio interference was completely unaffected by
a surge protector with filter choke - because that surge
protector filter choke is simply too small.
A common mode choke is actually a transformer. It's function is to
attenuate AC noise (greater than mains frequency) that affects both
phase and neutral equally using phase cancellation techniques.(Hence
the name common-mode choke).
These chokes are not designed based on their incductance as that is
not very high given their few turns and thick wire. They are designed
based on the ammount of current they have to carry as each winding is
in series with the load.
Unless your electronic appliance uses a switch mode power supply,
(Like a computer etc.), it is not mandatory to have this choke within
the appliance.
Surge protectors do not stop, block, or absorb surges. They
are called shunt mode devices for good reason. Their job is
to simply shunt (connect, distribute, short) a surge from one
wire to all others. No short, dedicated, and independent
connection to earth ground means the plug-in surge protector
only provides a destructive surge with more paths to find
earth ground - destructively through adjacent appliances.
I think you and I are on the same side here in that surge protectors
do not stop, block or absorb surges. They do indeed shunt or short the
surge as I have explained elsewhere in these posts. They do however
reduce the surge energy and thus protect the device they are connected
to. However, they do not do so from "one wire to all others" as you
say. A good surge protector as I have already mentioned, uses the
ground connector to discharge the surge energy. However, it is
perfectly acceptable to discharge this wrt neutral. As the purpose is
to protect the equipment downstream of the surge-protector. However,
you cannot use a 3 pin surge supressor on a 2 pin socket as the surge
circuitry would be effectively disconnected or now fire at double the
designed voltage depending on the design.
I think that we are at cross purposes here as to the scale of the
surge supressor. For a whole-house supressor, which is located at the
input of the AC mains to the house, by all means have an independent
ground. It is most probably required for a correct installation.
However, I entered this list at Halfgaar's question about a Surge
Protector Strip and those protectors do not require an independent
connection to ground.
Most engineering is a compromise between practicality, cost and
pragmatism. What is the cost of a professionally installed earth
ground? What is the cost of the TV set or stereo that you are
protecting? Which is more expensive? Also are you going to install all
the electronic/electrical equipment in your house in a tight circle
around the ground rod?
I am not denying the usefulness of a good ground. Just don't get
carried away by it.
A good quality surge supressor notes the critical importance
of earthing. Benchmarks in surge protection, such as
Polyphaser, don't discuss their product line in application
notes. Polyphaser discusses the most critical component in
any surge protection 'system' - central earth ground:
http://www.polyphaser.com/ppc_pen_home.asp
How important is earthing to Polyphaser? A product does not
even have a connection to earth ground. Distance to earth
must be so short that the Polyphaser product mounts directly
ON earth ground. But then those who know surge protector know
that Polyphaser is an industry benchmark. Therefore
Polyphaser discusses earthing - extensively.
No earth ground means no effective surge protection. So
plug-in protectors lie by telling half truths. They avoid all
discussion about earthing since they have none. A surge
protector is only as effective as its earth ground.
All this is probably quite true for a large scale surge suppressors
but probably not relevant to Halfgaar's Surge Protector. Believe me.
If it was, then there would be another regulatory requirement for it.
Again I reiterate a good ground is great but an adequate ground, does
the job.
Halgaar,I seem to be getting several conflicting answers here.
Basicly, all I'd like to know is: can I trust the surge protector (or
"parasite eliminator" or something as the manufacturer calls it) in my
extension cord (or power strip or whatever) to protect my equipment? Does
it at least do *any* good, or can I just leave it out?
This discussion is getting somewhat big, so I'd like a definate answer
Halfgaar
Depends where you live:
I don't really know what it's supposed to do. It was written on the box, at
I don't know about your particular case, but I tend to view these as
I'm Halfgaar, I believe you got me mixed up with Tube2c.
Where I come from, all cables are underground as well, but what about surges
Well, continuous 400V is not exactly a surge. A surge is usually hunders of
Halfgaar
From my point of view, you could easily be the one telling lies
. But fear ?Granted they do not help with surge protection, but in terms of increased
Yes! Unfortunately that is the way of the newsgroupFrom my point of view, you could easily be the one telling lies
You have a smart gut there Halfgaar feed him a beer from me
Yes that is fine. In many countries the neutral is actually tied toBTW, just to let you know: The voltage over phase and neutral is 226 here.
The voltage over phase and ground is 226. That falls within the 2 volt
limit, wouldn't you agree
cable is underground. The energy is still picked up by induction.
between 260 to 700 volts depending on the design. It is also not
duration, it may sometimes be called a swell. However, your case was
Well, to find that out, I have to open it up. It at least is psysicly
That way you will be absolutely certain.
The typical devices used as shunting element are voltage sensitive.
but should do wellAnd how exactly do I identify a shunt element? How can I see if there are
Won't the short powerinteruption be destructive to the devices connected toThe typical devices used as shunting element are voltage sensitive.
This means that at normal voltage they are very high impedance (Open
circuit). When a surge reaches the voltage at which the device
activates, the device goes into low impedance state (short circuit).
As soon as the voltage drops to normal, the device stops conducting
and goes back into open circuit state. This clamps the voltage at the
firing voltage of the device during a fault condition. Now if there is
a fuse or breaker and the surge is long enough in duration, the shunt
element (which is actually shorting your AC mains) will cause enough
current to flow that will cause the fuse to blow or breaker to trip
and thus interrupt the supply and protect the shunt element. If the
surge is short duration, the short is momentary and does not blow the
fuse or trip the breaker. (This is because a fuse or breaker responds
relatively slowly to the fault condition) so all that will happen is
that the voltage clamps to the firing voltage of the shunt element.
(And you will hear horrible farts in your stereo system
Sometimes people replace the fuse with one of a wrong rating or
response time (Or there isn't a fuse) and this results in spectacular
fireworks as the shunt device is destroyed due to the high currents
flowing through it.
Now why didn't I think of that. I know of the howstuffworks website. Thanks,I also found a website that explains surge protectors in fairly simple
terms (No numbers to satiate our friend w_tom
for you)
http://computer.howstuffworks.com/surge-protector.htm
The explanation is fairly simplistic in that it assumes a number of
things but it give a good enough picture of what goes on inside the
protector.
I gathered as much.