There are two major ways to protect your equipment from voltage transients. First, you can permanently install a device either before or after your electric meter—that is, at the point of entry. Second, you can install protection at the point of use, where sensitive pieces of equipment connect to electrical outlets. A combination of point-of-entry and point-of-use devices will provide the greatest level of protection.
The third edition of UL 1449 drills this down even further, and classifies SPDs into four types:
- Type 1 (point of entry). Permanently connected devices intended for installation before the service entrance disconnect (where the main power line enters the building, generally at the meter). These will have their own overcurrent protection—such as a fuse or circuit breaker—and were formerly called “secondary surge arrestors.”
- Type 2 (point of entry). Permanently connected devices intended for use after the service entrance disconnect. These can rely on the service entrance disconnect device for overcurrent protection.
- Type 3 (point of use). SPDs that are intended to be placed no more than 10 meters (approximately 33 feet) from the service panel, not including the length of the SPD conductors.
- Type 4 (component level). SPD components or assemblies, incomplete in and of themselves, that are intended for factory installation in other devices.
Panel-mount surge suppressors (UL 1449 type 2) can be installed in or adjacent to your electrical panels to provide protection throughout your facility. These panel-mount, or hard-wired, surge suppressors protect against transients that come through utility power lines (Figure 1). In addition, they can prevent transients that originate on one of your facility’s electrical circuits from affecting other circuits.
Figure 1: Panel-mount suppressors
This is an example of a panel-mount device for transient suppression, located in a small manufacturing facility.
Transients caused by lightning can enter buildings through underground circuits that supply electricity for sprinkler systems, pole-mounted lights, outbuildings, or other external uses. A transient on one of these circuits could damage equipment on other circuits unless it’s blocked by a suppressor at the electrical panel. Transients from lightning can also enter your building through telephone and cable-television circuits. Special hard-wired suppressors can be installed on these circuits by a qualified electrician.
Another way to provide whole-facility protection is to use a meter-based SPD (UL 1449 type 1). Note, however, that these devices can only be installed by your utility; check to see if it offers an installation service for this kind of protection.
Point of use: Plug-in surge suppressors
Plug-in surge suppressors provide affordable, but somewhat limited, protection for sensitive equipment. Often designed as power strips with multiple outlets, they protect only the devices that are plugged into them (Figure 2). Other plug-in surge protectors fit over wall outlets. Some models include jacks for telephone lines, cable-television lines, or USB devices.
With USB devices becoming increasingly common in commercial and industrial (C&I) environments, you may want more protection for sensitive equipment. USB devices that are moved off of the desktop can be vulnerable to PQ issues due to longer cable runs and varying power sources with differences in ground voltage, not to mention such real-world effects as moisture and vibration. On a factory floor, for example, the ground potential of a wall outlet and a piece of industrial machinery may be different. If a computer is connected to both (plugged into the wall for power, and plugged into the machinery via USB), the USB cable will conduct the potential difference (called a ground loop), and its circuitry may be overloaded. Inline USB isolators will protect equipment from ground loops, spikes, and surges. Many come with high-retention USB ports that require greater force for insertion or removal of USB cables, and the cables themselves can be made hardier to protect against electrostatic discharge (ESD) or electromagnetic interference (EMI).