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Black Box Explains...Optical isolation and ground loops.

Optical isolation protects your equipment from dangerous ground loops. A ground loop is a current across a conductor, created by a difference in potential between two grounded points, as in... more/see it nowequipment in two buildings connected by a run of RS-232 or other data line. When two devices are connected and their potentials are different, voltage flows from high to low by traveling through the data cable. If the voltage potential is large enough, your equipment won’t be able to handle the excess voltage and one of your ports will be damaged.

Ground loops can also exist in industrial environments. They can be created when power is supplied to your equipment from different transformers or when someone simply turns equipment on and off. Ground loops can also occur when there is a nearby lightning strike. During an electrical storm, the ground at one location can be charged differently than the other location, causing a heavy current flow through the serial communication lines that damage components.

You can’t test for ground loops. You don’t know you have one until a vital component fails. Only prevention works. For data communication involving copper cable, optical isolation is key.

With optical isolation, electrical data is converted to an optical beam, then back to an electrical pulse. Because there is no electrical connection between the DTE and DCE sides, an optical isolator— unlike a surge suppressor—will not pass large sustained power surges through to your equipment. Since data only passes through the optical isolator, your equipment is protected against ground loops and other power surges. collapse


Black Box Explains...DIN rail usage.

DIN rail is an industry-standard metal rail, usually installed inside an electrical enclosure, which serves as a mount for small electrical devices specially designed for use with DIN rails. These... more/see it nowdevices snap right onto the rails, sometimes requiring a set screw, and are then wired together.

Many different devices are available for mounting on DIN rails: terminal blocks, interface converters, media converter switches, repeaters, surge protectors, PLCs, fuses, or power supplies, just to name a few.

DIN rails are a space-saving way to accommodate components. And because DIN rail devices are so easy to install, replace, maintain, and inspect, this is an exceptionally convenient system that has become very popular in recent years.

A standard DIN rail is 35 mm wide with raised-lip edges, its dimensions outlined by the Deutsche Institut für Normung, a German standardization body. Rails are generally available in aluminum or steel and may be cut for installation. Depending on the requirements of the mounted components, the rail may need to be grounded. collapse


Black Box Explains...The difference between the SurgeArrest and power strips.

It says UL® listed, so it must be okay, right? Don’t be fooled. The $5.99 surge suppressor you picked up for your home PC may be nothing more than a... more/see it nowmultiple outlet extension cord.

UL® listed means that a product has been submitted to Underwriter’s Laboratories® for safety testing in certain categories. The strip protector you just bought is probably listed in the extension cord category. It won’t stop harmful surges from destroying equipment data.

The UL® listing for surge suppressors is UL® 1449. APC® SurgeArrest® products received the best UL® 1449 rating. Some vendors rate surge protection on the basis of joule energy. But let-through should be compared.

Basically, let-through is a measure of how much of a spike or surge each protector will let though to your electronic equipment. The lower the let-through rating, the better the suppression. And the SurgeArrest is guaranteed forever—even if it takes a catastrophic hit. It may be the last surge protector you buy. collapse


Black Box Explains...Power problems.

Sags
The Threat — A sag is a decline in the voltage level. Also known as “brownouts,” sags are the most common power problem.

The Cause — Sags can be caused... more/see it nowlocally by the start-up demands of electrical devices such as motors, compressors, and elevators. Sags may also happen during periods of high electrical use, such as during a heat wave.

The Effect — Sags are often the cause of “unexplained” computer glitches such as system crashes, frozen keyboards, and data loss. Sags can also reduce the efficiency and lifespan of electrical motors.

Blackouts
The Threat — A blackout is a total loss of power.

The Cause — Blackouts are caused by excessive demand on the power grid, an act of nature such as lightning or an earthquake, or a human accident such as a car hitting a power pole or a backhoe digging in the wrong place.

The Effect — Of course a blackout brings everything to a complete stop. You also lose any unsaved data stored in RAM and may even lose the total contents of your hard drive.

Spikes
The Threat — A spike, also called an impulse, is an instantaneous, dramatic increase in voltage.

The Cause — A spike is usually caused by a nearby lightning strike but may also occur when power is restored after a blackout.

The Effect — A spike can damage or completely destroy electrical components and also cause data loss.

Surges
The Threat — A surge is an increase in voltage lasting at least 1/120 of a second.

The Cause — When high-powered equipment such as an air conditioner is powered off, the excess voltage is dissipated though the power line causing a surge.

The Effect — Surges stress delicate electronic components causing them to wear out before their time.

Noise
The Threat — Electrical noise, more technically called electromagnetic interference (EMI) and radio frequency interference (RFI), interrupts the smooth sine wave expected from electrical power.

The Cause — Noise has many causes including nearby lightning, load switching, industrial equipment, and radio transmitters. It may be intermittent or chronic.

The Effect — Noise introduces errors into programs and data files. collapse


Black Box Explains...Why you should consider a UPS.

Downtime is unacceptable and often costly. But it’s impossible to get 99.9% uptime when you plug your hardware into an AC outlet.

Power problems are the most common cause of network... more/see it nowinterruptions. According to an IBM® study, the average system is hit by 120 power disturbances per month.

Have you ever had to reset the clock on your VCR or seen the lights dim for a moment when the refrigerator kicks on? These are common occurrences that are insignificant at home but can cause a shutdown in your network. Many power disturbances are so short they’re invisible to the human eye, but they can make a router lock up or a switch require rebooting. Power problems are actually more common than you may know. For instance:
• 34% of network downtime is because of bad power (IBM study).
• 99% of power problems are brownouts (low voltage) or blackouts (complete outages). Only a UPS protects against those.
• It takes 90.87 seconds for switches in non redundant networks to recover from power interruptions.
• 45% of all data loss is caused by power problems.

For a small fraction of the cost of your networking hardware, you can purchase a UPS that protects your network from blackouts, brownouts (low voltages), and surges—even lightning strikes!

To prevent power disasters before they happen, more than 70% of servers are protected with a UPS. Network managers know that having a server down brings many operations to a halt. Although the loss of a single hub or router may not bring the entire corporation to a standstill, it can result in zero productivity for entire workgroups or remote offices.

How can you tell if your system is suffering from power problems?

See if some of these symptoms are familiar: damaged hardware, numerous service calls, erratic operation, unexplained problems, unreliable data, system slowdown, damaged software, system lockups, and more.

If you’ve experienced some of these problems, you need a UPS. It will keep power flowing, giving you enough time to shut down safely during a power outage. It will also regulate your power, smoothing out dangerous overvoltages and undervoltages, spikes, surges, and impulses that often go unnoticed. These power anomalies can be caused internally by nearby machinery, fluorescent lights, and elevators, as well as externally from nearby transformer problems, lightning strikes, downed power lines, and more.

Data and equipment losses from power problems are preventable. Eliminate system downtime and increase profitability and productivity with a UPS.

When looking for a UPS, consider these steps:

1. List all the equipment you have that needs protection. Remember to include monitors, terminals, hard drives, external modems, and any other equipment in the critical path of potential power or surge sources.

2. Add up the total amperage ratings of your equipment. This information is probably imprinted on the back of each device.

3. Multiply this total amperage figure by the operating voltage (typically 120 VAC in the U.S.) to obtain your total volt/amp (VA) requirement with a safety margin.

4. Select a UPS with a VA capacity at least as high as the amount in Step 3. To accommodate for future expansion, it’s wise to order a device with an even larger VA rating.

5. If you have questions about which UPS is right for you, contact Tech Support. collapse


Black Box Explains...Power over Ethernet (PoE).

What is PoE?
The seemingly universal network connection, twisted-pair Ethernet cable, has another role to play, providing electrical power to low-wattage electrical devices. Power over Ethernet (PoE) was ratified by the... more/see it nowInstitute of Electrical and Electronic Engineers (IEEE) in June 2000 as the 802.3af-2003 standard. It defines the specifications for low-level power delivery—roughly 13 watts at 48 VDC—over twisted-pair Ethernet cable to PoE-enabled devices such as IP telephones, wireless access points, Web cameras, and audio speakers.

Recently, the basic 802.3af standard was joined by the IEEE 802.3at PoE standard (also called PoE+ or PoE plus), ratified on September 11, 2009, which supplies up to 25 watts to larger, more power-hungry devices. 802.3at is backwards compatible with 802.3af.

How does PoE work?
The way it works is simple. Ethernet cable that meets CAT5 (or better) standards consists of four twisted pairs of cable, and PoE sends power over these pairs to PoE-enabled devices. In one method, two wire pairs are used to transmit data, and the remaining two pairs are used for power. In the other method, power and data are sent over the same pair.

When the same pair is used for both power and data, the power and data transmissions don’t interfere with each other. Because electricity and data function at opposite ends of the frequency spectrum, they can travel over the same cable. Electricity has a low frequency of 60 Hz or less, and data transmissions have frequencies that can range from 10 million to 100 million Hz.

Basic structure.
There are two types of devices involved in PoE configurations: Power Sourcing Equipment (PSE) and Powered Devices (PD).

PSEs, which include end-span and mid-span devices, provide power to PDs over the Ethernet cable. An end-span device is often a PoE-enabled network switch that’s designed to supply power directly to the cable from each port. The setup would look something like this:

End-span device → Ethernet with power

A mid-span device is inserted between a non-PoE device and the network, and it supplies power from that juncture. Here is a rough schematic of that setup:

Non-PoE switch → Ethernet without PoE → Mid-span device → Ethernet with power

Power injectors, a third type of PSE, supply power to a specific point on the network while the other network segments remain without power.

PDs are pieces of equipment like surveillance cameras, sensors, wireless access points, and any other devices that operate on PoE.

PoE applications and benefits.
• Use one set of twisted-pair wires for both data and low-wattage appliances.
• In addition to the applications noted above, PoE also works well for video surveillance, building management, retail video kiosks, smart signs, vending machines, and retail point-of-information systems.
• Save money by eliminating the need to run electrical wiring.
• Easily move an appliance with minimal disruption.
• If your LAN is protected from power failure by a UPS, the PoE devices connected to your LAN are also protected from power failure.
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Black Box Explains...Remote power control.

Simply put, remote power control is the ability to reset or reboot PC, LAN, telecom, and other computer equipment without being at the equipment’s location.

Who needs remote power control?... more/see it nowAny organization with a network that reaches remote sites. This can include branch offices, unmanned information kiosks, remote monitoring stations, alarm and control systems, and even HVAC systems.

When equipment locks up at remote sites, it is usually up to the system manager at headquarters to reset it. Often, there aren’t any technically trained personnel at the remote site who can perform maintenance and resets on equipment. So, in order to save traveling time and minimize downtime, remote power control enables the system manager to take care of things at the office without ever leaving home!

Remote power control can be done with modems or existing or special phone lines. The ideal system uses “out-of-band management,“ an alternate path over an ordinary dialup line that doesn’t interfere with network equipment.

An effective remote power control system incorporates the following:
• An existing phone line, such as a line being used for a fax, modem, or phone.
• Transparent operation. The system shouldn’t interfere with or be affected by normal calls.
• Security features. The system should prevent unauthorized access to network equipment.
• Flexibility. System managers should be able to dial in from anywhere and control mulitple devices with one call.
• Have power control devices that meet UL® and FCC requirements. collapse


Black Box Explains…Sizing a UPS

The power delivered by a UPS is usually expressed both in volt-amps (VA) and watts. There’s often confusion about what the difference is between these figures and how to use... more/see it nowthem to select a UPS.

VA is power voltage multiplied by amps. For instance, a device that draws 5 amps of 120-volt power has a VA of 600. Watts is a measure of the actual power used by the device. VA and watts may be the same. The formula for watts is often expressed as:

Watts = Volts x Amps

This formula would lead you to believe that a measurement of VA is equal to watts, and it’s true for DC power. AC power, however, can get complicated. Some AC devices have a VA that’s higher than watts. VA is the power a device seems to be consuming, while watts is the power it actually uses.

This requires an adjustment called a power factor, which is the ratio of watts to VA.

AC Watts = Volts x Amps x Power Factor

Or:

Watts/VA = Power Factor

Simple AC devices, such as light bulbs, typically have a power factor of 100% (which may also be expressed as 1), meaning that watts are equal to VA like they are with DC devices. Computers have had a much lower power factor, traditionally in the 60–70% range. This meant that only part of the power going into the computer was being used to do useful work.

Today, however, because of Energy Star requirements, virtually all computing devices are power factor corrected and have a power factor of more than 90%.

Which brings us around to how to use this information to select a UPS. The capacity of a UPS is defined as both VA and watts. Both should be above the power requirements of the connected equipment.

Because of the computers that had a low power factor, UPSs typically had a VA that was much higher than watts, for instance, 500 VA/300 watts. In this case, if you use the UPS with a power factor corrected device that requires 450 VA/400 watts, the UPS won’t provide enough wattage to support the device.

Although UPSs intended for enterprise use now normally have a high power factor, consumer-grade UPSs still typically have a lower power factor—sometimes even under 60%. When using these UPSs, size them by watts, not VA, to ensure that they can support connected equipment.
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