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 wont 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 cant test for ground loops. You dont 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 suppressorwill 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
Power over Ethernet Surge Protector, 60-Volt Manual
Manual for SP075A (Version 1)
Black Box Explains…Sizing a UPS
Product Data Sheets (pdf)...Dual-Circuit Power Distribution Unit
Product Data Sheets (pdf)...Special-Application Surge Protectors
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
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.
Product Data Sheets (pdf)...Elite Managed Power Controllers
Product Data Sheets (pdf)...APC Rackmountable Smart-UPS Series and SmartSlot UPS Accessories
1-Port USB-to-USB Isolator Manual
Manual for SP386A, SP387A (Version 1)
Product Data Sheets (pdf)...Standalone, Vertical, and Rackmount AC Power Outlet Strips
Metered Rackmount PDU with Front and Rear Outlets, 20-Amp