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Surge Protectors, scams and saints
saturation:
Hello All:
I found the blogs by accident and was pleasantly surprised by a knowledgeable, enthusiastic, and honest appraisal of electronics and devices.
The review on audiophile equipment and cheap multimeters is exemplary.
One thing that is vital to review are plug in consumer surge suppressors. Many claims are made and almost none can be tested by consumers, and even engineers can't without the right high voltage equipment.
Like fuses, you only find out how good a surge suppressor is when it burns out to protect devices plugged into it. But the owner can't determine if a true serious overvoltage event occurred and was was thus saved by the surge suppressor, or simply the surge supressor blew on its own, from a defect or age. Without an event recorder, you'll never know.
Thus, the only way to know a surge suppressor works is if the fundamental design works, and tested to failure. This does not exist as I know, and neither Consumer Reports in the USA, or any other agency like UL, provide this type of testing. UL tests for safety, not function, and CR does not do in depth engineering tear downs.
It would be good to see EEVblog do a tear down of a surge suppressor in detail. You can make a whole series of this topic, as well as audiophile gear and multimeters, by going through each model and doing a torture test of each device, to prove their claims as EEVblog does with Fluke DMMs.
Just standardize you test suite, and go for it!
tomlut:
I used to work as an R&D engineer with a surge suppression manufacturer and would be really interested in this.
I've seen some shockers (no pun intended) over the years.
My basic observation would be, like in all things -you get what you pay for. Buy a $20 plastic multi-outlet power board and expect your house to burn down. Buy a + $100 metal housed version and you can be reasonably sure your investments will be substantially protected.
Having said that there are some awful tricks and misinformation in this industry. Take "transient response technology" for example. It was invented so that a particular manufacturer's products would pass UL approval, at the detriment to actual equipment protection. The device would only clamp fast pulses, it would not respond to slow over voltages (e.g. +150% supply voltage @ 50Hz). So your equipment would not be protected if two of the three phases shorted out or the neutral lifted down the street, but the device has a nice confidence inducing UL logo on it.
Another easily identified trick is to list "total protection" or the sum of the surge rating for each phase, when in reality each phase is only protected by 1/3 of the rating.
I know where you could get access to a 20kA 8/20µs surge generator if required. It's not portable, you'd have to travel to it :)
alm:
Just saw this topic for the first time, thanks for the informative review! It could be an interesting topic, I'm sure Dave could set up some test, possibly with the help of Doug. But it would be hard to simulate the extremely low output impedance of the mains supply.
It's hard to verify if a surge protector works without having all equipment twice, one plugged in in a surge protector and one in a normal power strip, or at least continuously monitoring the power quality. As long as no equipment dies, it might be just like the rock that keeps tigers away.
About the slow over voltages, is there anything a surge protector (without complex electronics like a UPS) can do against that? There's only so much energy that the MOV can convert to heat.
You talk about the fire risk, wouldn't (non-UL listed) equipment pose a similar risk if faced with a transient, for example from the EMI filter?
saturation:
Hello tomlut,
This was my first eevblog post, no one but you replied or seems to think its an issue. Over a year ago, I wrote and discussed the issue with 2 academic authorities, Martzloff formerly of NIST, and Dr. Standler, and why the industry has gone in bizarre ways.
http://www.eeel.nist.gov/817/pubs/spd-anthology/index.html
http://www.rbs2.com/fire.htm#anchor000001
http://www.amazon.com/Protection-Electronic-Circuits-Overvoltages-Standler/dp/0486425525/ref=cm_cr_pr_product_top
The issue of poor implementation is widespread for consumers, and less so in professional installations. The 2 biggest problems are:
Joule rating hype in MOV driven suppressors
"Serial mode" suppressors
Anyway, the Consumer Product Safety Commission has extremely rare reports of fires caused by SPD devices since 2000, so from UL's viewpoint, safety has improved, but function remains, unknown.
The only maker I trust these days for home plug in suppressors is APC, but I still disassemble them and analyze the design of a particular model before I buy more. So far, I've not had one that was badly made.
The once revered Tripp Lite, famous for its Isobar and metal enclosure, well I've had 2 that were very badly made, again the only way to find out is to open them.
Belkin, Philips, and other names not associated with electrical manufacturing, caveat emptor. An anecdote from Amazon about Belkin versus APC:
http://www.amazon.com/Belkin-F5C895-TEL-SurgeMaster-8-Outlet-Protector/dp/B00000J1RU/ref=wl_it_dp_o?ie=UTF8&coliid=I3RZVU2J95MR80&colid=EIWMTQB99Q0R
Although crude and sensationalistic, this website covers the key issue with photos on consumer SPD fires:
http://www.sfowler.com/investigations/Surge%20Protectors.htm
The good news is that newer designs for MOV are more fire resistant. Also the UL revision for SPD from early 2002 provide more fire retardant issues in designs, so to have UL SPD approval, you need to implement these changes. Alas, a simple solution is to tape the MOV together so if it flames out or explodes, the hot shrapnel is contained and keeps from jumping into the power rails. Fast blowing fuses are now built into some MOV, or discrete devices are placed inline with them, so if they conduct, the fuse will blow before the MOV does.
In APC designs made to conform to the most recent UL mandate, blast containers are built into the casing, so when the cases are joined, the blast compartment encloses each MOV set. There are no screws inside many APC SPD, the reason being if fire or an explosion does occur, the metal screw doesn't fly inside as another piece of shrapnel. APC PCB are snapped together inside the plastic case, and IMHO personally tracking what could happen, if a fire did occur, the whole blast casing and the body will melt down into the PCB, potentially suppressing the fire.
Alas, again its presumptive, to be sure we need a destructive test to see it actually fail.
Why fires occur isn't because the SPD becomes a hand grenade, but because most SPDs are mounted behind furniture, or on rugs, often covered with lint or dirt. If it gets hot enough, it will ignite items around it.
--- Quote from: tomlut on June 05, 2010, 03:26:41 pm ---I used to work as an R&D engineer with a surge suppression manufacturer and would be really interested in this.
I've seen some shockers (no pun intended) over the years.
My basic observation would be, like in all things -you get what you pay for. Buy a $20 plastic multi-outlet power board and expect your house to burn down. Buy a + $100 metal housed version and you can be reasonably sure your investments will be substantially protected.
Having said that there are some awful tricks and misinformation in this industry. Take "transient response technology" for example. It was invented so that a particular manufacturer's products would pass UL approval, at the detriment to actual equipment protection. The device would only clamp fast pulses, it would not respond to slow over voltages (e.g. +150% supply voltage @ 50Hz). So your equipment would not be protected if two of the three phases shorted out or the neutral lifted down the street, but the device has a nice confidence inducing UL logo on it.
Another easily identified trick is to list "total protection" or the sum of the surge rating for each phase, when in reality each phase is only protected by 1/3 of the rating.
I know where you could get access to a 20kA 8/20µs surge generator if required. It's not portable, you'd have to travel to it :)
--- End quote ---
tomlut:
This is in reply to alm's post. Will get back to you ASAP saturation. But as usual the life of an oncall tech is never dull. Duty calls...
It's not that hard to test. The let-through voltage can be measured easily and the CBEMA curve can be used to find a pass/fail voltage (for the output pulse width).
Your point about the low impedance of the mains supply is an interesting one. It is only low impedance at low frequencies. Once you get to the end circuit of an ELV installation the inductances can be large enough to generate substantial ringing voltages even occasionally from induced currents from nearby lightning strikes.
There is absolutely something that can be done about slow over voltages. Let the protection device self destruct. It should (safely) shunt the current and trip the circuit breakers, just like a crowbar circuit. e.g. As long as the output voltage can be limited until the breakers trip your $10,000 home theatre setup is protected and it only costs you the price of some new surge protection ($100s range for domestic). A transient discriminatory protector will let your expensive equipment bare the brunt of the fault but be fine for the next fast impulse. You tell me which would you prefer?
The particular example of fire risk I was referring to was the example of a couple of unfused 8kA disk MOVs across the A-N lines of a $20 plastic power board. MOVs will flame if overloaded under certain conditions and all manufactures of MOVs recommend a metal housing and appropriate fusing as a minimum precaution. If you bought a $120 metal enclosed protector you would not be exposed to this risk. They are not EMI filters as such (though they will offer some low pass filtering). Generally the good ones have a high (10 to 40kA) main surge protection element, a big chunky low pass filter (not at all like the little silver boxes with an IEC connector I think you are referring to) and then some secondary surge protection in the order of 5 to 10kA.
The cost of UL approval means there are some excellent protection devices out there without this qualification - if you know what you are looking for. Also there were moves to close this particular loophole as I left the industry. Haven't followed it up lately.
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