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  1. #1
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    Can an old surge protector affect the circuit it's plugged into?

    Can an old surge protector affect the circuit it's plugged into?

    This is a hardware and electrical question, and I'd appreciate any comments about the following odd situation.

    I installed solar photovoltaic panels on our garage roof, which are connected through a voltage inverter directly to the house circuit breaker box. The solar panels communicate with a monitor through the neutral wire of the house wiring (powerline communication). The panels begin their operation when the sun rises and also begin communicating with the monitor at that time. Everything seems to work well EXCEPT in the following situation: if I have an old surge protector plugged into a house receptacle when the solar panels begin operation in the morning, then the solar panels have difficulty establishing communications with the monitor. If I unplug the surge protector, then it seems that communication is established and the system operates normally. While it's difficult to know cause/effect because there are so many variables, I am wondering about this question:
    Can an old surge protector affect the circuit it's plugged into and/or feed back into the house wiring some sort of interference which might make it difficult for powerline communication to operate ?

    Thanks for any comments or other sources of information.

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  3. #2
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    RF,

    Exactly what kind of surge protector and how old? It it is a standard power strip type the MOV's die over time so you may be having some kind of interference caused by this. Note: I'm no electrician I'm just taking a stab from things I've read. HTH
    May the Forces of good computing be with you!

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  4. #3
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    The surge protector says "PowerSentry" on the front. All it has are six receptacles and a switch. On the back it says Model 100133, made in China, relocatable power tap, E87630

    It is pretty old, but I have no idea how old it is. I'm sure it's cheap and came from Walmart or maybe Radio Shack.

    I don't know much about how surge protectors work, but could imagine that they have a capacitor or Zener diode or something that may short out the high frequencies that the powerline communication uses.

  5. #4
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    I suspect the PV array uses high frequency control signals over the mains cable and the surge protector filters them out (absorbs them).

    I'm sure there's an echo here....

    cheers, Paul

  6. #5
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    I agree with Paul. I think the surge protector is seeing the HF Comm as surge and clipping it. You could put the surge protector on a clock and shut it off when the solar is trying to communicate with the Monitor. Find out if there is an auxiliary cable to connect the panels to the monitor separate from the mains.
    Try this: Take a 10 foot extension cord and wrap it around an Iron bar or a toroid ring as many times as you can. Wrap it with tape. Plug the surge supressor into this cord. This is a HF power cord filter so the supressor never sees the com signal.

  7. #6
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    A surge protector usually uses three MOVs (Metal Oxide Varistors) on the AC line. One between the Hot and Ground, another between Neutral and Ground and a third between Hot and Neutral.

    An MOV looks like a disc capacitor, and is non-conductive, but when one or more of them it receives a high voltage transient it will shunt (short) the circuit, usually tripping the fuse or breaker for that circuit.

    Small surges will degrade it. Degradation is defined by the manufacturer's life-expectancy charts that relate current, time and number of transient pulses. The main parameter affecting MOV life expectancy is its rating in Joules. As the energy rating increases, its life expectancy increases exponentially, the number of transient pulses that it can handle increases and the "clamping voltage" (at which it will shunt itself) it provides during each transient decreases.

    As can be expected with something that shorts itself, "catastrophic failure" of a MOV can result in a bit of a "flame out", which can and does start fires. If your surge protector in in an isolated location, with nothing flammable near it, it may not cause any problems. But if it's under a desk or workstation on carpet or with curtains or drapes in close proximity, the potential for fire is very real. See this.

    If any of the MOVs are leaky they could easily be causing problems for your powerline communications setup. My advise? Stop using the old surge protector. No surge protection is better protection in this case.

    We use several power strips, but surge protectors are banned in my house.

  8. #7
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    MOV are high capacitance device. Like a capacitor, it presents a short to RF (high frequency signal). Like previous post says, may use 8-ft or longer pure extension cord to isolate the MOV equipped power strip. The inductance of the 8-ft cord is enough to effect RF isolation.

    UL, Underwriter Lab, tries to resolve this MOV-induced fire problem. [I have no relation with UL besides being a consumer]. I open and studied some MOV equipped connectors and power trips. On UL Listed Philips products (made in China), the MOVs are covered by fire-proof cloth. It also has relay to trip open. Both help to prevent fire. Some other brands will trip open (from the AC outlet) when the MOV is shorted. That is, the product is no longer usable, forcing consumer to discard it.

    Some brands, especially old products, just have LED lights telling you if 'you're protected' or not. It simply means if the MOV is functional or not. It does not trip open to disconnect from AC outlet.
    Yes, old MOV type power strip should be discarded. DIY people and hackers may opt to open it and remove MOVs, turning into an ordinary power strip.

    Usually. if MOV induces fire, it is not that MOV is below voltage rating. To cause it to burn by over Wattage, it must have sustained high AC voltage several times higher than the nominal 120V. AND has to be for a few minutes as well. It actually means the AC line is super seriously malfunction. The house wiring needs immediate attention. Without the MOV, PC will burn. Maybe it is a good trade-off.

    If hit by lightning, MOV, only few Watts, may explode by the tremendous Wattage imposed on it. But without MOV, maybe the PC catch fire or explode and sparks fly. Or your telephone/TV is exploding. (All the more not to use phone during lightning.)
    I am not sure burning up MOV or MOV fire is better, or exploding PC or phone/TV, and sparks fly from them is a better preference.
    Last edited by scaisson; 2013-11-14 at 08:00.

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  10. #8
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    The only surge protectors I use are the Trip Lite ISOBAR. No cheap plasic here to catch fire.

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    I have seen plenty of damage from power surges and the only effective solution is a quality online UPS. These units isolate the PC from the mains providing protection from all manner of supply fluctuation, not to mention saving your data when you have a power outage.

    cheers, Paul

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    An MOV is a Metal Oxide Varistor: Voltage dependent Non Linear resistor. All of the fires in them have been caused by Very heavy over voltage of long duration. You can usually tell when to check them because the clock, TV and refrigerator exploded, and the power strip blew up. In this case the power strip is the least of the worry if the solar panel gets hit by lightening, but: he can still isolate the power strip by making the extension cord filter. It doesn't even take an extension cord if the power strip cord is long enough. The inductance of the power cord is not working as a filter as evidenced by the original problem. Using the cord to make a Lo-pass filter may be worth a try.

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    Seriously, use an extension cord in series with a 1500 Watt power strip? Wake up folks. Aside from being extremely frowned upon by any Inspector from your insurance carrier and your local Code peeps, your will regret this move. Never mind the fact that the number of turns required to block the line impressed signal would take many more turns than the cord has length regardless of core material...

    I would not be surprised if inside the power strip there is at least one small coil of wire (called an RF inductor) on a form shunted to the neutral or/and ground wire. It is being used as an RF Shunt and measured in Henrys (Henrys, milli and micro). It is this coil(s) that is shunting your impressed signal to ground. Better arc suppression power distribution units used them to perform what we call high frequency noise suppression on the a/c line. During the early days of X10 ? systems, these RF Coils were found to interfere with their line signals as well. Primary reason for these coils was to suppress strong, local AM and FM transmitter signals from causing chaos on sensitive equipments in labs, RF shielded test enclosures, etc. MOV's in good condition have no sensitivity to low level HF (anything above 120HZ) impressed signals. Period.

    Using a UPS to replace a MOV power strip is just plain stupid. Instead of replacing a burned up power strip once hit, you will be replacing the UPS or installing new MOVs into it. UPS's should be used for the sole purpose of supplying line power during an outage or drop-out, perhaps with an uprated power strip in front of it to hopefully take the hit before it gets to the UPS. BOTH, are considered sacrificial equipments for surge suppression - just a matter of what costs more to replace / repair. UPS's included surge suppression devices to improve their life expectancy but do take hits and the UPS dies or loses its protection waiting for the next hit that kills the digital circuitry inside down the road. APC warranties and others exist only to sell their product, given that the number of claims they get pushed into honoring are something like winning your local lottery, are more than paid for by the buyers falling for the warranty gimmick. MOV's are the cheap person's surge suppression tool. There are much better tools out there, but cost more money. MOV's can initialize fires, but it is extremely rare as better ones are made of materials that do not burn, ever. They can and do blow up, crack, get extremely hot and arc, and ignite materials around them, but burn? Nah. These surrounding materials are what ignite. Buying a plastic cased strip could burn your house down. Use only metal housed, fast acting FUSED, strips with fire rated sockets. Circuit breaker protected and slow-blow fusing react too slowly as tested by many labs NIST. UL. etc. Yes, the Tripplite (ISOBAR 6 socket and larger) did make some of the better consumer products years ago, but I can not verify their current product line as meeting my criteria. Commercial level units will cost you hundreds, not tens of dollars. And for those with some deeper pockets, you can always buy a house-wide suppression device at your local electrical products supply house. It sits across your 220 VAC house feeds and shunts to a real ground (you know, the one located at your power pole, or like me, two 8 foot copper rods just outside my wall fed by two inch wide silvered braid), inside your metal panel if you are worried about line conducted surges, but it will do nothing for strikes in your back yard that set up a large radiated EMP spike near your TV. Anything you do not want to replace should be in fed through interactive surge suppression if you live in an area designated as prone to such things. Many utilities have added surge suppression to their lines but they too may eventually fail out leaving your plastic, $5 strip as the final barrier. Buy a line monitor, with or without a recorder, or a scope and tie it to your line and you will see for yourself how often stuff happens and what sizes your are constantly subjected to. Keep in mind that these devices protect ONLY line conducted surge spikes.

    I have had probably twenty near-miss ground strikes (some depressions are still viewable) over the years, and untold line spikes of 1000VAC or more, and only lost equipment, once. Then I opened up some books.

    School's out.
    Last edited by mpioso; 2013-11-15 at 03:23.

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  15. #12
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    I will agree with you in that there are many opinions floating around and some of them occasionally get loose. I can see that you have read much and learned a little. Knowledge is wonderful, a little knowledge can be dangerous. Your opinion of UPS's is such. Your poinion of RF chokes is also. It is clear that you don't understand how they work. The extension cord idea works well and I use it extensively in my work at a large electronics firm. Yes the cord has to be sufficiently sized for the job. I doubt that he is pulling 1500 watts from his power strip. MOV's do attenuate HF signals. You have knowledge of expensive solutions when what is needed is effective solutions.

    Philomel , MsEE
    School's never out!

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  17. #13
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    MOV device is high capacitance device. They do shunts HF (High Frequencies). But its shunting effect is frequency dependent (Zc=1/(2*pi*f*C). Otherwise, the powerline AC 50/60Hz would be shunted or shorted!
    As you can see from the Zc equation, the higher the frequency, the smaller the impedance of the capacitor. When freq is infinite, even small capacitor has zero impedance (aka a short)! At zero freq, the equation shows infinite resistance. Zero freq is DC. So capacitor blocks DC.

    Inductor impedance, Zl=2*pi*f*L. At infinite freq, even a tiny TINY L blocks totally. (But L can never be zero because a wire is inherently an inductor unless it is zero-length wire). At zero freq, L is zero resistance to it. That is, inductor allows DC to go through unimpeded. Its resistance to freq, however, is frequency dependent; the higher the frequency, the more resistance. (People may now argue that DC is impeded by DC resistance, R. But R=V/I, there is no frequency dependency. Zero freq and infinite freq will be treated equally by an R.) People in the know recognize Z and R, real and imaginary parts. I try to make it more understandable here.

    The usage of L in power strip is to isolate frequencies between the ends of the L. Keeps them apart, so to speak. The size of inductance depends on the isolation level and at what freq you're targeting (but not affecting the freq you want).
    For capacitor, you want to 'kill' the signal right at the capacitor (shunting, not blocking). Or to use capacitor to block DC between the ends of the capacitor.

    X10 operates at 121kHz. You can calculate the effect by MOV and inductor in the circuit.
    On MOV effect on powerline communication: Powerline Ethernet Adapter (networking using powerline) runs at Mega-Hz, much higher than X10. As such the high capacitance MOV is detrimental. Their application write-ups advise against plugging it into MOV equipped AC outlet or power strips.

    Powerline Ethernet Adapter is a sophisticated device. It adapts to conditions and noises in the powerline to effect a maximum communication channel. It changes in situ in frequencies, amplitudes, phase angle, constellation positions, etc.
    X10 is a much simpler device. Transmission is low bit content and low bit rate, but gets things done at minimal cost. It operates on a single 121kHz, digital transmission is at zero-crossing on the powerline AC wave.

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  19. #14
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    Thanks to everybody for your comments. I learned a lot. All I did was remove the old surge protectors and everything has been working fine now. I do have a UPS protecting my important pieces of equipment. The rest of my household equipment can be easily and cheaply replaced and didn't really need a surge protector anyway.

    So thanks again !!

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    Quote Originally Posted by Rfarmer View Post
    I do have a UPS protecting my important pieces of equipment.
    After reading the above, then why did you contract facts and assume a UPS does surge protection. Well, yes, it does claim surge protection. And then read its numbers. Its hundreds of joules mean near zero protection. Basically protection from transients that do not do damage. Often a surge too tiny to damage other appliances can destroy the undersized protector circuit inside a UPS.

    Your concern is a surge that is maybe hundreds of thousands of joules. For many times less money (per protected appliance), you can installed protection that makes typically destructive surges irrelevant.

    Protection is always about where those hundreds of thousands of joules dissipate. Destructively if inside a building. Harmlessly if earthed BEFORE entering. The later solution is the only solution used in facilities that cannot have damage. And for you is a least expensive solution.

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