AC Power Surge Protection?

A friend recently had her audio system damaged from an AC Power Surge.

Would like to prevent this so Googled using AC Power Surge Protection and found "The Best Surge Protector by Brent Butterworth.

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Read link "Surge Protectors ??? (Brickwall, Zero Surge, Furman, SurgeX,"

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Then did a Forum search and found some very long discussions such as: Surge Protectors

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Surge protector fuse blown

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I do not have a technical background so would be interested in others comments concerning all this.

Would like to use your advice to build a cost effective audio protection system.



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** AC power voltage surges damaging audio gear are so rare that I cannot accept it as true without convincing evidence.

The DC power supply inside each piece of audio gear usually contains a transformer, rectifier and filter electros - a combination that eliminates AC voltage spikes/surges better than anything you can possibly buy or build.

OTOH, the term "power surge" is regularly used to explain away sudden failures in almost any electronic device - when the real cause is simply a bad component.

.... Phil

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Phil Allison

Phil Allison prodded the keyboard with:

Best Regards: 
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That may be true if the stereo or whatever is not attached to other devices. Once you connect things together, damage from power surges starts to happen.

It's quite common with computer network gear. Interconnected ports fail, while the main switch chassis or network attached printer or computer continue to work.

Service entrance surge surpressors protect against this sort of issue.

power surges and the damage they cause are very real problems.

FWIW somebod mentioned powervar and Oneac devices, it wasn't clear what these devices were, but if they were isolation/filter units, they work great.

Stuff from tripplite is pure junk, had many of their devices catch on fire, without surges. It was always caused by poor crimps and junky power switches or bad assembly.

APC power strips are better, never had one self destruct yet.

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Cydrome Leader

Excellent information on surges and surge protection is at:

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- "How to protect your house and its contents from lightning: IEEE guide for surge protection of equipment connected to AC power and communication circuits" published by the IEEE in 2005 (the IEEE is a major organization of electrical and electronic engineers). And also:

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- "NIST recommended practice guide: Surges Happen!: how to protect the appliances in your home" published by the US National Institute of Standards and Technology in 2001

Both guides are from reliable sources.

The IEEE surge guide is more technical.

I wouldn't rely on the testing that was done. There are standard tests for surge protectors - 600V is not one of them (6,000V is). And I have no idea if their test is representative of a surge. There is related information on UL testing in the IEEE surge guide under "2.2.3 Surge Limiting Voltage"

The vast majority of surge protectors use MOVs as the voltage limiting element (over 90% according to the IEEE surge guide). These protectors do not use MOVs. I have not seen them evaluated by a reliable independent agency, and I would not use them. They, of course, claim to be better than the MOV based ones. Some of their arguments are downright stupid.

Westom is an internet nut that googles for "surge" to spread his ideas about protection. He has joined an astonishing number of forums to spread his ideas. Some of them are good, some not-so-good, and some are complete nonsense. Everything he says about plug-in protectors is complete nonsense. How can you tell? Westom says plug in protectors don't work. Both the IEEE and NIST guides say they are effective.

I am "bud". I got tired of westom's crap after seeing it on several Usenet groups I watch over a short period. I have nothing to do with the surge protection industry other than I am using a couple protectors. A lot of what I wrote here comes from the IEEE and NIST surge guides

w_tom is a name that westom used to use. More nonsense.

I have not read either of these threads.

If using a plug-in protector all interconnected equipment needs to be connected to the same protector. External connections, like coax also must go through the protector. As explained in the IEEE surge guide (starting page 30) plug-in protectors work primarily by limiting the voltage from each wire to the ground at the protector. To do that all wires must go through the protector.

The NIST surge guide suggests most equipment damage is from high voltage between power and signal (phone, cable,...) wires. Computer and video equipment is likely more at risk than audio. And it depends on where you are. Some parts of the US have significant surge exposure. The major cause of damaging surges is lightning. Normal and abnormal utility operations can also cause damaging surges.

The author of the NIST surge guide looked at the surge current that might come in on power wiring (US). The source was a 100,000A lightning strike to a utility pole adjacent to a house with typical urban overhead power distribution. Only 5% of strikes are more powerful and this is, for practical purposes, the worst case. The surge current was 10,000A per wire. Service panel protectors with much higher ratings are readily available. High ratings mean long life. A service panel protector is likely to protect anything connected only to power wiring (most audio systems?)

The author of the NIST surge guide also investigated how much energy might be absorbed in a MOV in a plug-in protector. Branch circuits were

10m and longer, and the surge on incoming power wires was up to 10,000A (wort case, as above). The maximum energy at the MOV was a surprisingly small 35 joules. In 13 of 15 cases it was 1 joule or less. There are a couple simple reasons the energy is so low (one of which may be particular to US wiring). Any UL listed protector in the US will have ratings higher than that, and much higher ratings are readily available (as in your first link). Again high ratings mean long life.

(Neither service panel or plug-in protectors protect by absorbing a surge. They do absorb some energy in the process of protecting. And protection from a direct strike to a building requires lightning rods.)

In the US, since 1998 UL has required thermal disconnects for overheating MOVs. (With world markets they are probably included by all competent manufacturers everywhere.) APC had an engineering error resulting in a recall.

The IEEE surge guide describes how the protected equipment can be connected across the MOVs, or be connected across the incoming power wires. If connected across the MOVs, the protected equipment will be disconnected on failure. (That is one reason why manufacturers can have protected equipment warranties.) I think the IEEE surge guide says UL requires protectors to state if they do not disconnect the protected load with the MOVs.)

It would be nice if you could compare protectors based on joule rating. The IEEE surge guide explains that (US) there is not a standard way of measuring this, so some manufacturers have misleading ratings. Some other (reliable) manufacturers responded by not including joule ratings.

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** My comments were intended to exclude the effects of a lightning strikes hitting the ground.

AC supply voltage spikes are normally caused by inductive loads going on and off.

** If by 'power surge' you actually you mean lightning strike.

... Phil

Reply to
Phil Allison

** Connecting MOVs to ground like that in a *plug-in device* is prohibited on safety grounds under EU and similar regulations as followed in most 230/240 V places - like Australia where I am.

MOVs either have or can develop after some use leakage currents well in excess of the maximum permitted, which is only a milliamp or so for most categories of appliances.

The only components that may be so connected are agency approved " Y caps " with values like 4.7nF - while MOVs and " X caps" always go across the line.

... Phil

Reply to
Phil Allison

I think the US-UL permitted leakage for "appliances" is 0.5mA (which of course is at 120V).

Standard practice in the US for plug-in protectors is MOVs from H-N, H-G, N-G. And if signal wires go through the protector, they are limited to ground also.

One of the reasons the energy at a MOV in a protector is so low (US) is that at about 6kV there is arc-over between service panel busbars and the enclosure. This appears to be an intentional feature. (The voltage across the established arc is hundreds of volts. Since the enclosure is connected to the earthing system that dumps most of the surge energy to earth. And a required N-G bond at the service limits the N surge voltage.)

A significant (and likely major) cause of surge damage to equipment is high voltage between power and signal wires. If MOVs are only connected H-N and there is a large surge the voltage drop on H & N will likely increase the voltage between power and signal wires (6kV at the service would result in about 2kV from the H & N to the 'ground' reference at the service panel). It then would be inadvisable to use plug-in protectors on equipment that has both power and signal wires.

The normal failure mode for MOVs is after sufficient energy hits they start to conduct at lower voltages, eventually conduct at 'normal' voltages, and go into thermal runaway. Thermal disconnects then operate(at least in the US). I would think a H-N MOV with 1mA leakage @230V would be near thermal runaway.

I don't know how surge protection is done down-under. It works here. Some features here may be from the relatively high exposure to thunderstorms in parts of the country. They are uncommon or nonexistent in many parts of the globe.

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** I really doubt using three MOVs like that is *normal* practice - certainly one never sees it in entertainment electronics or test gear, whether made in the USA or elsewhere.
** The fact that MOVs deteriorate means it is hazardous to have them wired from active to safety ground. Same argument goes for regular metallised film capacitors which also deteriorate when exposed to AC supply voltages - then explode.
** Takes at least 10mA to get a typical MOV device hot.

.... Phil

Reply to
Phil Allison

Entertainment electronics may have some surge protection but is not intended to protect against major surges.

As can be seen from the IEEE surge guide, 3 MOVs is absolutely standard practice in the US.

Because of the additional risks added by having only H-N protection in plug-in protectors (as in my last post) I suspect 3 MOVs is common practice elsewhere, H-N only protectors can increase risk, not reduce it. Gareth does not know what is connected H-G. You do not necessarily know what the specific requirements are for plug-in protectors elsewhere.

All the packaging protectors come in that I have seen indicate what the protection is (H-N, H-G, N-G). I suspect it would elsewhere. I am not interested in looking.

In the US the likely maximum surge energy at a MOV in a plug-in protector is a tiny 35J, and that includes for the largest probable power line surge (as in my 1st post). The simplest UL listed protector here will have a joule rating far above that.

The joule rating of a MOV is the single event energy that will put the MOV at defined end of life (but still functional). Looking at MOV ratings curves, if the MOV gets single hits that are far below that, the cumulative rating is far above (like over 10x) the single event rating. Failure is real unlikely. Coupled with high ratings, that is why some companies can have protected equipment warranties.

The author of the NIST surge guide has written "in fact, the major cause of [surge protector] failures is a temporary overvoltage, rather than an unusually large surge." An example of temporary overvoltage would be a high voltage distribution wire coming down on the 115/230V secondary conductors.

You could also say it is hazardous to have leakage and fault currents on the safety ground.

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It isn't acceptable for US medical devices, but it isn't unknown, either. It's always combined with a fuse, where I've seen it.

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