A Shock to the System

November 1, 2008
John V. Hinshaw

LCGC Europe

Volume 21, Issue 11

This month in "GC Connections", in the first of a two-part series, John Hinshaw relates what happens when high-voltage spikes attack modern electronic equipment, what to do when they occur, and how to set up equipment to minimize damage and loss of data.

While I was finishing a cup of morning coffee and watching the news a few weeks ago, the room lights brightened suddenly to twice normal. At the same time the cable-TV converter box barked out a loud "SNAP", flashed brightly and sent smoke signals my way as if to say, "Help me!" in a metallic voice. The TV screen turned blue and then faded to black as the room lights dimmed to nothing. After turning off the power switch on the surge suppressor connected to the TV and converter box, and making sure there was not a fire, I ran upstairs to check on the computers. I glanced at the fire extinguisher on the landing at the top of the stairs and hoped I would not need to use it. Meanwhile, the lights came back on. The computer screens — my wife Beth and I both have our own desktops — were normal save for small messages from the attached interruptible power supplies (UPS) that reported a power "incident". I feared a repeat occurrence, so I shut down the computers and unplugged everything from the wall sockets. Then Beth called me into another room where she smelled smoke. The surge suppressor in there was blackened around its sockets and had actually scorched the carpet. I unplugged it and then went around the rest of the house looking for more burnt-out items and unplugged whatever I found, running or not. I went into the garage to check the electrical breaker panel. One breaker had tripped, but when I threw it to the on position, the garage door opener emitted a loud humming noise and signalled displeasure by turning on its light — not normal — so I flipped the breaker off again, climbed up a ladder, and disconnected the unfortunate opener. I found that the kitchen microwave oven was in good shape as I reheated my now cold cup of coffee and began to compose a mental list of damaged household electrics that we would report to the insurance company.

While many LCGC Europe readers work in large companies that effectively take care of the issues of electrical fault protection and data stewardship, there are many who might not have an effective plan, or perhaps do not believe that implementing one is cost effective. My home electronics situation is not a workplace, but there are some lessons here that can be applied to the needs of chromatographers who want to conserve their data and their equipment in a working environment.

Laboratory Power

After the surge had subsided, I waited for what seemed to be a reasonable time and, finding no further power instability, I plugged in and restarted the various electrics around my home. Beth said she would call the power company and our insurance, so I headed in to work. I wondered if a surge had hit there as well and I tried to picture how the various pieces of laboratory equipment and office computers were connected. Was there a surge suppressor on that computer? What would happen if the gas chromatographs were hit with 1000 V?

As I paused at the stoplights on the way to work, I glanced up at the electrical power poles on the street and observed the two sets of wires. On the top, three high-voltage lines — charged to several thousand volts, at the least — were positioned over some apparently lower-voltage lines and canister step-down transformers hung precariously on a few widely spaced poles. The lower lines were connected to cables that led into buildings along the way. I had heard stories about automotive accidents or storms that caused high-voltage lines to drop across a transformer or onto the lower voltage lines. Suddenly, this seemed like a real possibility and it worried me that every day there was some chance that a large voltage surge, fluctuation, or blackout would come my way again.

A quick word about lightning strikes is in order here. No point-of-service consumer surge protector will keep attached equipment from harm if lightning scores a direct hit on power lines at the street or building level. Dedicated equipment expressly for this purpose should be installed by professionals if lightning strikes are a concern. It is said that lightning never strikes twice in the same place and in Oregon, where I live, it hardly strikes at all. But the chances of encountering another power problem loomed large in my mind.

Later that morning, I took the time to walk around the laboratory and look beneath my desk to discern how the computers, instruments and other equipment were connected to the AC power. I already knew that the chromatographs were hooked up to dedicated power circuits. Most commercial gas chromatographs are guarded by so-called crowbar fault-protection devices that supplement surge protectors and prevent sustained over-voltages from passing into the main instrument circuits. When the input voltage exceeds a predefined limit, the protective device is triggered and places what amounts to a short circuit across the input AC. This draws a large current through fuses on each side of the AC line and quickly disconnects the system as the fuses open. These are single-use devices, like automotive air bags, but they are very effective at stopping high input voltages. The sidebar story illustrates just such an incident.

In the laboratory, the computers and test equipment were connected haphazardly. On one bench, I found two computers and a network switch connected through a smallish surge suppressor. The rest of the equipment was simply plugged directly into wall sockets, and there were no additional surge suppressors in sight. A number of the wall-socket pairs were orange colored with a triangular symbol embossed on them, however, and I later learned that these were connected through surge suppressors in the electrical room and, therefore, protected, although I did not know to what degree that protection might extend. In my office, the computer was not plugged into an orange socket but the monitor and desk lamp were, so I exchanged the computer and the lamp plugs and hoped for the best for the time being.

Keeping surges away from the computers is one part of a comprehensive data and equipment protection plan. My company has a good policy in place for data conservation through backups and archiving. We follow a regular routine of making daily backups to tape of all of our critical data such as source code, company documents, e-mail, databases, production records, and so-on. The tapes are stored off-site in a secure vault so that, should there be a fire, theft, electrical problem, or other destructive event, we will be able to recover all of the mission-critical data in short order. At home, the situation was not nearly as well controlled and now I was more than ready to put some extra thought into it.

How Much Protection?

Later that morning, Beth contacted the power company, whose representative told her that there had indeed been an unspecified "incident" at the local substation and gave her instructions on how to file an insurance claim. That evening we tallied up the damage: one dishwasher, one garage door opener, three surge suppressors and the network switch in the home office. This last item was an unexpected failure, because it had been plugged into one of the large surge-suppressing uninterruptible power supplies that I had installed a few years back. And come to think of it, the pyrotechnic demise of the cable-TV converter was as unexpected: it, too, had been plugged into a fairly new surge suppressor. I began to see the outline of a more deeply rooted problem so I did a little research on surge protection.

Surge protection device (SPD) performance is specified by the American National Standards Institute (ANSI) and Underwriters Laboratory (UL) standard ANSI/UL 1449.1 A device that is listed under this standard must meet certain criteria for equipment protection during transient voltage spikes that appear on the power lines inside a building. Essentially, all consumer SPDs, such as those sold in office supply or electronics stores, meet ANSI/UL 1449. These are the power-strip style cord-connected, or direct plug-in voltage transformer "cubes" sold for electronics or computer protection, including such devices as part of a UPS. Permanently wired devices, such as those I found at the orange wall sockets at work, also fall into the group of devices that can be listed under this standard. Any device intended for medical use falls into a different, stricter category and would not be listed under ANSI/UL 1449.

Most SPDs employ metal oxide varistor (MOV) devices, nonlinear variable resistors that exhibit a high resistance at normal line voltages and a low resistance at voltages approaching and above a characteristic limit voltage level of the device. When a high-voltage spike occurs, the MOV will present a low resistance and conduct the excess voltage around the connected equipment instead of allowing it to connect across the equipment. The maximum voltage presented to connected equipment during a spike is called the clamping voltage. Each time a MOV is presented with a spike a little cumulative damage occurs to the device. Eventually it will wear out. The most common failure mode is an increase in the clamping voltage followed by a complete failure to clamp a spike at all.

ANSI/UL 1449 calls for applying a series of multiple spikes across the SPD at 6 kV and 500 A and at 3000 A. The rated clamping voltage must not degrade by more than 10% during the tests. Most manufacturers rate their SPDs at a more conservative 1000 V: the 6 kV ANSI/UL tests are designed to stress the device to an absolute maximum level and do not represent normal operating conditions. The standard also requires testing for continuous duty at 125% of the normal rated voltage (150 V for a 120 V rated device) and for a short-term fault at 240 V to simulate the accidental loss of the electrical neutral somewhere in the system. There are also tests for end-of-life simulation, leakage current and high-potential dielectric strength, or "hi-pot". Through all of this, a listed SPD must not show any evidence of potentially starting a fire or presenting a shock hazard. ANSI/UL 1449 recently underwent a third revision that will be required of SPDs next year.

All of this sounded impressive to me until I considered the rated output clamping voltage level — the level to which the output voltage of an SPD can rise during a spike — of commonly encountered surge suppressors. The lowest (best) voltage rating available is 330 V, and this is the level found in consumer SPDs intended for 120 V operation. This means that almost three times the normal AC voltage can come right through an SPD and be applied across a television, a computer power supply, a 12 V DC supply that powers a network switch, or laboratory equipment before the MOVs cut in to suppress the surge. The clamping voltage will be maintained until the supply drops below it or the MOV fails.

Here, then, was an explanation for the immediate failure of the network switch. I plugged in its 12 V adapter and found zero output voltage — the transient clamped voltage of about 330 V was just too much for it and had opened something in the transformer or rectifier circuits. As for the cable-TV converter box, it too had not withstood the sustained high voltage. Fortunately, as Beth reported, the cable company was happy to provide a new, upgraded cable box in exchange for the older, fried one. "Happens all the time", the representative had said.

The duration of the transient spikes used in testing was another eye-opener for me. Before I researched this question, I had assumed that a "spike" or "transient" comprised a time span ranging from very short to perhaps as long as 10–20 s; I had not previously thought through the implications of small components carrying thousands of volts and amps for extended durations, but in such situations they are guaranteed to fail, sometimes spectacularly. In fact, the spikes that are administered under ANSI/UL 1449 are quite short, on the order of tens of microseconds. These are good simulations of the kind of repetitive transients that occur as a result of remote lightning strikes, power company switching transients and other normal occurrences, but they do not come close to the kind of sustained over-voltage conditions that my home experienced for a second or two. In such situations, the affected MOVs in an SPD can simply explode from overheating, after which, the full input voltage will hit any connected equipment.

That the only surge suppressor to fail catastrophically was the oldest one shows how MOVs degrade over time, with the gradual accumulation of damage from repetitive high-voltage transient hits. And by the way, this SPD was, in effect, installed incorrectly — it was allowed to rest on the carpet next to a media stand where it could have caused a fire. The new one is on a shelf in the stand, which I hope will be good enough if and when another failure occurs. I am lucky that the TV and DVD player attached to it are no worse for the experience, although I wonder if their lifetimes have been compromised. Only time will tell. Since then, I have replaced all of the surge suppressors and uninterruptible power supplies. After being hit with a destructive surge of unknown magnitude and duration, there was no way to know if they would function correctly again, either when hit with a momentary transient or a sustained over-voltage condition.

Next

What are the implications for laboratory equipment? The reliable production and conservation of quality results is a most important concern in the laboratory, second only to personal and environmental safety. The proliferation of modern PC technology into laboratories and laboratory instruments, and their deep level of integration with the final products of analytical laboratory operations — the results and associated data — makes an appropriate plan for damage control and remediation a requirement for the technologically current laboratory. Not having such a plan in place leaves an opening for the inevitable disaster. It could be a sudden event such as I experienced, or it could come as an eventual failure of a computer or instrument that will take the laboratory off line for some indeterminate time.

Back at home, to add insult to already injured electronics, 36 h after the surge hit I had another major failure that demonstrated the subtle nature of electrical fault damage. I will relate this final jolt in the next instalment of "GC Connections", along with some recommendations for how to anticipate and control laboratory electronics and equipment damage from electrical causes, including the basics of electrostatic discharge (ESD) control.

References

1. ANSI/UL 1449, Standard for Transient Voltage Surge Suppressors, Second Edition (Underwriters Laboratories, Northbrook, Illinois, USA, 1997).

"GC Connections" editor John V. Hinshaw is senior staff engineer at Serveron Corp., Hillsboro, Oregon, USA and a member of the Editorial Advisory Board for LCGC Europe. Direct correspondence about this column should be directed to Alasdair Matheson e-mail amatheson@advanstar.com