How HUMplug-e ground loop solver works ?

Anyone has experience on this HUMplug-e product ?
Web page http://www.21best.com/21_best/electronic/security/video/filters/for_sale_.html
says: " Simply plug your equipment through this, to cure it of Ground Loops. Filters out unwanted voltage and current in the ground line that cause ground loop hum while simultaneously maintaining a solid, safe ground."
I have experience on many different way on solving ground loop loop problems in audio/vidoe systems. Practically every other types of products listed on that page are known to me in details (I have used similar produicts, know what is inside such items, even manufactured some quite simlar products). I have written some material on ground loop solving to http://www.epanorama.net/documents/groundloop/index.html
How this HUMplug-e product works makes me wonder. Given the specifications (15A current) and a small size it can't be an isolation transformer. According the description it keeps the solid ground connection it just can't be a "cheater" plugs that just simply cuts ground connection (dangerous peactice that is not recommended).
My quess that it does some magic on ground connection so that it stops/reduces the current that can flow on normal ground loop case, but still lets the ground connection to be good enough for electrical safely. I am just wondering how this is done in such what that it works and meets the electrical code safey requirements. Anyone has experience on how this is implemented ? Some of my quesses would be those impklementation possibilities: - some common mode coil type construction over all wires - two parallel diodes (on different directions) wired between input and output ground connections (stops current when voltage difference is low but will pass hort circuitfualt currents at low voltage drop)
Anyone commenting my quesses how this device works ? Anyone has experience on this ?
One quess is that this HUMplug-e could be based on circuit similar to Figure 3 - A High Current Safety Loop Breaker Circuit at web page http://sound.westhost.com/earthing.htm
Description of the web page: "The loop breaker works by adding a resistance in the earth return circuit. This reduces circulating loop currents to a very small value, and thus breaks the loop. The capacitor in parallel ensures that the electronics are connected to the chassis for radio frequency signals, and helps to prevent radio frequency interference. Finally, the diode bridge provides the path for fault currents. The use of a large chassis mounting (35A) type is suggested, since this will be able to handle the possibly very high fault currents that may occur without becoming open circuit. Note the way the bridge is wired, with the two AC terminals shorted, and the two DC terminals shorted. Other connection possibilities are dangerous, and must be avoided."
"In the event of a major fault, one (or more) of the diodes in the bridge will possibly fail. Semiconductors (nearly) always fail as short circuit, and only become open circuited if the fault current continues and 'blows' the interconnecting wires. High current bridge rectifiers have very solid conductors throughout, and open circuit diodes are very rare (I have never seen a high power bridge go open circuit - so far at least). Use of the bridge means that there are two diodes in parallel for fault current of either polarity, so the likelihood of failure (to protect) is very small indeed."
This circuit installs a circuit consisting of diodes, resistor and capacitor the grounding wire. Would using this kind of circuit on groudn path be electrically safe and/or legal in this kind of application ?
--
Tomi Engdahl (http://www.iki.fi/then /)
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Tomi Holger Engdahl wrote:

No but is sounds as if the HUMplug has a circuit similar to the one you found...except it may have a 15 amp bridge rather than a 35 amp one.

The basic idea is that the ground loop is "busted" with a 10 Ohm resistor. (That may or may not actually cure a hum problem, depends on the sensitivity of the amplifier circuits involved) It does, however, provide a reasonable ground path for static charges and RF filter leakage.
To "short" RF noise to ground a capacitor is placed across the 10 Ohm. This will not take care of frequencies in the "hum" range.
Finally a heavy current bridge is connected in such a way that it passes current both directions. This might seem to be short that is placed across the 10 Ohm resistor, but the truth is that these diodes are non-linear devices. Their incremental impedance in response to small signals depends upon the DC current through the device. Look at the slope of the Diode forward bias curve. That it flattens out near zero current is the key. But if there is a ground fault, and heavy current occurs, the diodes pass the current with minimal voltage drop and allow the tripping of breakers and fuses.
The device is "legal" so long as it's just plugged in to an outlet (like the HUMplug) but as for "safe", that is another question! My personal feeling a 35 Amp bridge is too small and a 15 amp bridge is dangerous. You want the bridge to be large enough to trip breakers and blow fuses. I'd use a 100 amp bridge for circuits fused in the 30-50 amp range (as many are). Most diodes take a pretty healthy pulsed current, and failing open is more rare than shorted, but still you should always remember the rule: SEMICONDUCTOR DEVICES MAKE MUCH BETTER FUSES THAN FUSES! You obviously don't need a heat sink of the kind that might be needed to handle a continuous 100 amps but the higher the current (and voltage...you don't want the diodes failing from a high voltage spike either!) rating the better. You may have problems finding a bridge module over 50 amps, but four 1000 volt 100 amp stud diodes are not big deal.
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wrote:

Could it simply be a ferrite-based toroidal choke placed in series in the ground lead? It would safely maintain the safety continuity, but the high impedance would reduce the ground currents.
H. R.(Bob) Hofmann
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The ferrite choke would be "high impedance" only at high frequencies. It would do nothing for typical ground- loop currents.
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wrote ...

Yes, I wonder how "high" an impedance he thinks a small toroid is going to be at 50/60 Hz!
MrT.
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With suitably selected big ferrite core and more than few turns it is very well possible to get millenries even at 50 Hz. For example 10 mH inductance at 50 Hz is around 3 ohms impedance. This value will definately reduce ground loop currents on normal situations, but would it be then too much to make the grounding connection not good enough for electrical safety.
So my question is would any impedance value that is well effective for solving round loop problems too high to be added to the safety ground connection (would not be safe in rela life and/or woudl not meet safety regulations) ?
I have made ground loop solving products that have been connected audio and/or video lines. I have made many experiments on different constructions. For signal lines I have tried different ferrite material, toroidal cores (simular as used in toroidal mains transformers), E-cores etc.. Different contructions have their all good and bad properties. With suitable ferrite selection is possible to get inductances that are high enough for solving ground loop problems on signal lines. The downside is that materials with what I can get high inducances with reasonable number of turns tend to saturate quite easily.
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wrote:

Uh, ignoring core losses and other parasitics, you'll get whatever inductance you get inductance you get at ANY frequency. You don't get "millihenries at 50 Hz", you get millihenries.

Yeah, and to get 10 mH, you'd need a LOT "more than a few turns." And unless you wound it with sufficiently large-gauge wire, you'd have a fair amount of resistance as well.
Why you'd want any appreciable impedance in a safety ground could be a puzzle to some.
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In alt.engineering.electrical snipped-for-privacy@cartchunk.org wrote:
| wrote:
|> > > Could it simply be a ferrite-based toroidal choke placed in series in |> > > the ground lead? It would safely maintain the safety continuity, but |> > > the high impedance would reduce the ground currents. |> |> > The ferrite choke would be "high impedance" only at high |> > frequencies. It would do nothing for typical ground- |> > loop currents. |> |> With suitably selected big ferrite core and more than few turns |> it is very well possible to get millenries even at 50 Hz. | | Uh, ignoring core losses and other parasitics, | you'll get whatever inductance you get inductance | you get at ANY frequency. You don't get "millihenries | at 50 Hz", you get millihenries. | |> For example 10 mH inductance at 50 Hz is around 3 |> ohms impedance. | | Yeah, and to get 10 mH, you'd need a LOT "more | than a few turns." And unless you wound it with sufficiently | large-gauge wire, you'd have a fair amount of resistance | as well. | | Why you'd want any appreciable impedance in a safety | ground could be a puzzle to some.
If they don't know about the ground loop problem. The metallic interconnect between equipment is what makes this so hard. There is the loop being formed.
Maybe more effort needs to be put into why it is that the ground gets so much current induced into it.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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There are many ways to induce current.
The one thing thats clear to me is, providing some RFI filtering to the ground along with hot and neutral, is good.
Who is going to buy one of these hum gadgets and find out whats inside?
greg
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"GregS" wrote ...

If they're smart, they potted it. Likely the only way to prevent easy reverse-engineering (and subsequent cloning in some cheap far- east factory.)
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On Tue, 19 Jun 2007 05:28:29 -0700, dpierce wrote:

Only if the core is air, or vacuum.
The permeability of any ferromagnetic core varies with frequency, hence the inductance of a coil wound on such a core will vary with frequency, too.Some ferrites would be totally useless at 50 Hz. Laminated silicon iron stampings would work at 50 Hz and be no good at, say 100KHz.
This is different from "core losses", which are resistive.
The *apparent* inductance will be affected by winding capacitance as well. Above its self-resonant frequency, an "inductor" looks like a capacitor.
There's nothing wrong with Tomi's statement.
--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
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