Power Protection

Smart strategies for converging AV and IT systems.

All too often, your service call ends up like a script for a police forensics TV show. Perhaps we could call it CSI: Equipment Room.

It’s a mystery. Over a short period of time, several critical components have succumbed to premature failure, and for no apparent reason. No nearby lightning strikes. No mis-wiring of power circuits. No other signs of severe or catastrophic power problems. But the damage is done. You make the required replacements or repairs, perhaps absorbing all or part of the costs, and apologize to your client for the service interruption.

And you hope it doesn’t happen again.

All Too Familiar

However, thanks to the expanding scope and complexity of converged AV and IT systems, this scenario has become all too familiar. With today’s proliferating technologies, installations of all types, in residential, commercial and educational settings, are packed with more sensitive, microprocessor-laden components. That, in turn, means more potential points of degraded functionality or complete failure. If one control component fails, an entire system can be rendered useless. Never before has that proverbial “ounce of prevention” been more critical.

A thorough postmortem would likely reveal that many, if not most, of these mysterious failures are the result of hidden, but persistent, anomalies in the AC power service supplied to the components. Rather than the sudden, catastrophic failure induced by a lightning strike, we’re looking at the slow, cumulative effect of less severe but constantly repeating spikes and surges over a prolonged period. Rather than sudden death dealt by a single blow, it’s more like a slow poisoning.

Before outlining strategies for protecting vital AV and IT systems from such failures, it would be helpful to quickly review the structure of power systems and look for the origin of potential problems.

ABCs Of Protection

Power supplied by the public utility enters the building at the service entrance. Power protection inserted at this point, termed Category C, deals with major surges introduced to the building from the power grid. On a national basis, only about 20% of all power surges potentially present at the equipment rack originate outside the building, either from lightning strikes on power lines (which vary greatly on a regional basis) or issues on the power grid itself.

Certainly, lightning is a major threat. A lightning strike can generate more than 30 million volts and deliver 100,000-plus amps of current. However, the surge energy that could be delivered through a building’s wiring is limited to about 6000 volts and 3000 amps due to arcing and/or catastrophic failure of wiring. In any case, power surges passing through this point are relatively rare and usually are identifiable either by the presence of a storm or widespread power anomalies affecting a large area.

Protection at this level is largely a “brute-force” solution that is hardwired in front of the breaker panel. It mitigates external surges, such as nearby lightning or errant grid switching, but the high turn-on threshold allows lesser surges to pass through unaffected. Service entrance protection can degrade gradually over time, and it does not address other problems, such as over/under voltage conditions or spikes and surges generated within the building. Any insertion of Category C protection normally is accomplished by the grid provider, whose surge protection obligations often end at this point.

The remaining 80% of power problems occur within the building, and require protection strategies either at the branch circuit level (Category B) or point of use (Category A), which means either in the equipment rack or adjacent to the connected components. Providing adequate protection here usually is the responsibility of the AV or IT contractors who are installing connected equipment.

Local Culprits

As just noted, the high threshold of Category C protection allows low-level surges to pass through, and these are added to other spikes or surges generated within the building. (A spike is a high-energy, high-frequency event whereas a surge is a more protracted power swell.) Where do these anomalies originate?

A great many are the result of switching transients. These are created by on/off switching of high-current devices, such as large power amplifiers, other components with switch-mode power supplies or appliances with electric motors, such as refrigerators or air conditioners. Though less dramatic than lightning strikes, these continual low-level voltage surges not only threaten to degrade sensitive electronic components but also slowly chip away at the protection offered by typical MOV-based surge protection.

One study found that the typical piece of office electronics is subjected to more than 50 of these surge events on a daily basis. The immediate effects are often unnoticed, though they occasionally surface as computer lockups, crashes or equipment memory loss. Over the long term, cumulative effects can be the same as those wrought by a single catastrophic event: sudden and inexplicable failure.

Related Issues: O-V/U-V, RFI/EMI, IC

Before moving on to solution strategies, it’s important to note three other maladies that can affect AC power, each introducing its own set of problems.

Sustained over- or under-voltage: If the line voltage rises well above, or drops well below, the nominal voltage (120V in North America), some sensitive electronic components could be damaged. Over-voltage is rare and usually results from an error in wiring or connections. Under-voltage is somewhat more common, resulting from an overstressed grid going into “brownout” conditions. Many comprehensive power protection units will cut power to connected devices when over- or under-voltage passes a dangerous threshold.

Electromagnetic and radio frequency interference: AC line current can be “polluted” by extraneous signals induced from various sources. Although certainly no threat to a toaster or refrigerator, this interference can be problematic for sensitive digital electronics. Comprehensive protection systems will filter out this interference.

Inrush current: Switching on several high-current devices at one time can cause an inrush of current that trips the local circuit breaker. Some comprehensive protection systems will incorporate a “soft start” circuit to prevent transitional circuit overload.

Core Protection Strategies

Surge protection is the core of any strategy for protecting delicate AV and computer equipment from premature failure from either a catastrophic event or cumulative degradation from repeated low-level surges.

Minimal, low-budget solution: This approach inserts a basic surge suppression device that typically consists of a simple circuit incorporating a metal oxide varistor (MOV). An MOV is made from a semiconductor material that can conduct large amounts of current when presented with a voltage spike well above its nominal rating. When this happens, the MOV diverts the voltage surge to the neutral or ground, bypassing the “hot” AC terminal of the connected device. If properly rated for its application, and if still working at full rated capacity, such a device can be an adequate safeguard against sudden catastrophic failure.

There are downsides, however, to this basic approach. MOVs slowly degrade over time, with each small surge gradually diminishing effectiveness, giving these devices a finite lifetime. If used to protect critical equipment, they need to be monitored and tested at regular intervals, and replaced when effectiveness is suspected to be marginal.

Also, MOVs are “sacrificial” devices, meaning that it’s “once and done” protection. As soon as it is called on to divert a high-level threatening surge, the MOV has to be replaced. Also, when used in power filtering applications, MOVs can overheat and present a fire hazard, although most devices also incorporate a thermal fuse to prevent thermal runaway.

Finally, most solutions employing this approach will divert energy to the electrical ground, the same ground used as the reference ground for low-voltage signal circuits. This sudden appearance of unwanted current on the ground wires can disrupt data transmissions and lead to cascading problems.

Advanced solution: There are devices available for installers featuring surge protection technology that provides a significantly more sophisticated solution. These are not “sacrificial” devices, meaning that they’ve been designed to withstand continual surges without degradation, including high-level “lightning strike” types of events.

High-quality units of this type employ a two-stage approach to essentially eliminate both catastrophic and low-level surge events. The first stage employs opposing air core inductors designed to withstand surges up to 6000V, effectively blocking the high-frequency, potentially catastrophic events. A second stage eliminates the residual low-frequency surge voltages that can accompany the external high-voltage events, as well as eliminating repeated low-level surges originating from electrical activity in the building. Also, because this design does not rely on diverting current to ground, there is no ground contamination or common mode disturbance that could affect analog or digital low-voltage systems.

Many Series Mode units also offer a complete package deal. Because of their greater sophistication and circuit complexity, and relatively higher cost, they will also incorporate features for EMI/RFI filtering, over- and under-voltage protection, and inrush current management.

Apply As Needed

The best location (or locations) for insertion of surge protection solutions will depend on a variety of factors, including the size of the installation, relative location and grouping of critical devices on common circuits, the presence of any surge-inducing equipment on the circuit, and the particular sensitivities of each device.

Again, some service entrance protection may be provided by the electrical contractor, but this is general protection to prevent fires and avoid catastrophic damage to the primary electrical systems. It will be up to the AV or IT supplier to assure that appropriate protection is provided for the installed systems, and that the protection will be maintained for the expected lifetimes of those systems. The best way to assure appropriate protection is to keep it as close as possible, given reasonable logistical and budgetary constraints, to the point of use.

Power protection systems are designed to deal with problematic and potentially damaging anomalies on a functioning power grid. When the grid quits, that’s another issue and it calls for an uninterruptible power supply (UPS) to maintain critical system functions on an interim basis.

But keep in mind that not all UPS units provide complete isolation or adequate surge protection features. Don’t ask your UPS to do a job it wasn’t designed to do.

In larger and more sophisticated installations, whether commercial or residential, it can be helpful to have remote monitoring and control of the power devices serving critical electronic systems. To that end, manufacturers of power protection systems have introduced comprehensive, IP-based hardware and software solutions that allow internet access to check system status and diagnose current or potential problems.

A basic rackmount unit in this category enables the user to monitor and control power distribution settings, remotely power cycle equipment, monitor power usage over time, and display real-time power and energy usage, all via IP-enabled two-way communication. This is in addition, of course, to the extended capabilities of premium series mode units as outlined earlier.

Sophisticated Solutions

For the most critical applications, sophisticated solutions are available that include comprehensive on/off scheduling, as well as an auto ping mode that periodically checks compatible network and DSP devices to ensure that they are functioning normally. If repeated pings are unanswered, the unit is automatically power cycled and checked again. These solutions are available in a number of form factors for freestanding, rackmount or branch circuit installations.

Solving mysterious deaths may make for good TV drama, but what repeated onsite service calls can do to your bottom line can be a downright crime. Rather than investigating the calamity after the fact, you’re better off ensuring that appropriately scaled, comprehensive power protection is fully enabled from the outset.

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