IEEE Std 1100-2005
The following are excerpts from the IEEE Emerald Book: IEEE Recommended Practice for Powering and Grounding Electronic Equipment
3.4.3 Surge protection
Surges can have many effects on equipment, ranging from no detectable effect to complete destruction…electronic devices can have their operation upset before hard failure occurs. The semiconductor junctions of electronic devices are particularly susceptible to progressive deterioration…few solid-state devices can tolerate much more than twice their normal rating. Furthermore, data processing equipment can be affected by fast changes in voltage with relatively small amplitude compared to the hardware-damaging over voltages…For large surge currents; this diversion is best accomplished in several stages. The first diversion should be performed at the entrance to the building with a second protective device at the power panel or at the terminals of a connected load, or both…
TPD Comment: IEEE recommends multilayered or staged surge suppression strategies to protect today’s sophisticated electronic loads. As power supplies get mass produced and more cheaply made, and circuit boards get smaller and smaller (and therefore more sensitive to even small transient surges), the need for surge suppression and filtering is critical in today’s world.
4.4.5 Potential impact of EMI
Depending on the severity of the surge and the susceptibility of the equipment, three types of occurrences are possible (in addition to damage caused to cables and conductors): data disruption, hardware stress, and hardware destruction.
126.96.36.199 Type-I, signal-data disruption
Signal-carrying circuits are susceptible to surge interference via conduction, inductive and capacitive coupling, and electromagnetic radiation. Both near-and far-field phenomena affect these circuits as EMI. When surges are actually observed on signal lines, it’s often assumed, just because the signal circuits are still working, that the noise is below the circuit’s EMI threshold, and things are therefore acceptable. This is not so…
TPD Comment: IEEE recommends surge suppression on exposed data lines to reduce or eliminate failures or lockups due to noise or radiated interference that gets on and contaminates lines. Regardless of whether the disturbance comes from the electrical power system or is inductively coupled onto the lines from a nearby lighting strike (anywhere up to a quarter mile away), data lines need protected.
188.8.131.52 Type-II, gradual hardware stress and latent failures
A single lightning or switching surge often causes immediate, but not readily apparent physical damage to semiconductor devices. This damage then finally appears at some late time at which point the failure is obvious. This once controversial, but now accepted condition is called latent semiconductor device failure. For example, a single larger surge or several repetitive exposures to lower magnitude surges often cause a gradual performance deterioration, which may finally be associated with intermittent equipment operation as opposed to immediate catastrophic failure of the semiconductor device. In such cases where the semiconductor itself has had its performance marginalized, it is often difficult to differentiate between software-and hardware-induced errors.
TPD Comment: Everyone knows that a single lightning strike or other large surge event can cause immediate destruction to a circuit chip. But, even if the remaining energy actually getting to circuit boards from a lightning strike is not large enough to destroy the board, the effects of the surge energy will cause premature failure at some point in the future. Even if lightning and power company surges would never happen again, overtime circuit boards and power supplies will prematurely fail due to an accumulative effect of internally generated transients. And, before total failure the deteriorated chips slow processing functions and cause intermittent errors, lockups, and reprogramming issues. This is why IEEE is recommends both surge protection (for large impulses such as lightning) and high frequency filtering (to prevent gradual degradation to circuit boards and electronic loads. A TTLP power filter on the breaker panel is the most cost effective way to protect all loads.
184.108.40.206 Type-III, immediate hardware destruction
The third possible impact of surges is the immediately obvious and total destruction of hardware components in a single incident. Table 4-6 shows the threshold voltages and energy levels for destruction of selected semiconductors that are commonly used in electronic equipment (see Gallace and Pujol [B14] and Greason [B18]). Similarly, larger devices, such as signal and power transformers, and relay coils; and power supply components, such as chokes and capacitors, can be destroyed. Type-III events also include general arc-over damage within equipment.
TPD Comment: To prevent catastrophic destruction of equipment due to large surge events, TPD and IEEE recommend a staged protection system. At a minimum, protection on the electrical panel directly feeding the equipment as well as protection on the upstream panel is recommended. Whenever only one electrical panel exists, the panel protection plus point of use protection (with a quality series installed SPD) provides sensitive electronics with at least two stages of protection).
220.127.116.11 Surge protective device considerations
Recommended practice is that SPD’s be applied to service entrance electrical switchboards and panelboards, and panelboards located on the secondary of separately derived systems that support ITE, telephone, telecommunications, signaling, television, or other form of electronic load equipment (refer to 8.6 for further details). These devices may be installed externally or internally to the switchboard or panelboard. Panelboards are available that contain integrally mounted SPD’s that minimize the length of the SPD conductors, thus optimizing the effectiveness of the device. However, as pointed out in IEEE PO62.72 (Draft L.1 November 2005) [B-2], when an SPD is located inside switchboards or panelboards, there is a concern that failure of the SPD can cause collateral damage to the switchboard or panelboard, including compromising the insulation system with subsequent L-L and L-G faults.
It is recommended practice that all SPD’s have a means to disconnect them for service. Locating the SPD external to the switchboard or panelboard allows the disconnecting means to be located inside the switchboard or panelboard and does not require access to the switchboard or panelboard interior when servicing the SPD.
TPD Comment: Although integral surge suppression may sound like a good idea at first impression, almost nobody asks about what can happen when the integral suppressor fails. The potential for arc flash liability and the potential for collateral damage from failed surge suppressors inside the panel should give all cause for concern. Also, today most facilities do everything they can to avoid downtime, such as adding backup generators, dual redundant switchgear, uninterruptible power supplies, voltage regulators, surges suppressors, filters, power conditioners, etc. Why would those facilities add a surge suppressor to the inside of a panel or switchgear when catastrophic failure of the suppressor could bring down the panel or switchgear?
8.6 Lightning/surge protection considerations
…A listed and properly rated surge protective device should be applied to each individual or set of electrical conductors (e.g., power, voice, and data)…all voice…secondary surge protectors should be coordinated per…UL497A-1998…
TPD Comment: IEEE recommends that in addition to power protection, incoming lines such as phone, cable and satellite entry points should be surge protected. What this does not explain is that this refers to all data and communications lines. In custom homes, office complexes and school campuses this means it is recommended to protect dozens if not hundreds of incoming and outgoing communications lines (such as CAT5E, RS233, feeds from security cameras, wires from outdoor speakers, etc.).
The selection of surge protective devices typically depends on the location of the device. The surge protective devices are recommended to be sized per IEEE Std C62.41-1991 and IEEE Std C62.45-1992 requirements to achieve proper coordination. Surge protective devices should be listed to UL 1449-1996. Surge protective devices used for three-phase, four-wire circuits are generally recommended to be connected in all combinations of line-to-line, line-to-neutral, line-to-ground, and neutral-to-ground. Surge protective devices for three-phase, three-wire circuits are recommended to be attached in both the line-to line and line-to-ground modes. Surge protective devices may also be specified with high-frequency filtering characteristics.
TPD Comment: IEEE recommends that the AC power suppressor protect all modes. Accordingly, some low end residential grade surge suppressors and lightning arrestors with L-G protection only, may not provide sufficient protection for today’s larger home and facilities with sub panels (where neutral and ground are separated per code). IEEE also acknowledges that use of a high frequency filter is a good practice when it comes to protecting certain electronic equipment. TPD offers various power filters which contain both surge suppression and high frequency filters.
SPDs may not perform properly under field conditions of use unless installed in a correct manner. Recommended SPD installation practice is for all lead lengths to be short and shaped to minimize open loop geometry between the various conductors. This is accomplished by removing excess and unneeded lead lengths to the SPDs; by twisting all the phase, neutral, and equipment grounding conductors together; and by avoiding any sharp bends and coils in the conductors. IEEE Std C62.41 and UL 1449 should be used as standard means of verifying performance of surge protective devices.
TPD Comment: IEEE recommends that parallel mounted surge suppressors should be installed with minimal wire to the system. This means that the unit should be mounted in such a way that connecting wires are as short and straight as possible.
8.6.3 Service entrance surge protection
Facilities housing electronic load equipment of any type should have service entrances equipped with effective lightning protection in the form of listed Category “C” SPDs, as specified in IEEE Std C62.41. Care should be taken to assure that the method used for the installation of surge protective device equipment does not cause a degradation of its current-diverting and voltage-clamping abilities.
TPD Comment: IEEE recommends using surge suppression capable of handling Category C type surges on high exposure areas. The AC power suppressors TPD recommends for breaker panels, landscape lighting, gates, fountains etc. are all designed to address large impulses such as lightning, utility, and other types of externally generated catastrophic surges.
8.6.4 Premise electrical system surge protection
In addition to SPDs installed in the service entrance equipment, it is recommended that additional surge protective devices of listed Category “B” or Category “A,” as specified in IEEE Std C62.41, be applied to downstream electrical switchboards and panelboards, and panelboards on the secondary of separately derived systems if they support communications, ITE, signaling, television, or other form of electronic load equipment…
TPD Comment: IEEE recommends protecting all sub panels in addition to protecting all service entrance panels. The most critical panels to protect are those directly feeding electronic loads. Those critical panels are typically the sub panels in larger homes and facilities. In addition to surge protection, TPD strongly recommends that the protection device protecting any panel feeding electronic loads also contain a high frequency filter (reference 8.6.1).
8.6.5 UPS system surge protection
Lightning and other transient voltage and current-producing phenomena are harmful to most UPS equipment and to its served electronic load equipment. For example, the transient may reach the critical load via an unwanted activation of an unprotected static-switch bypass path around a UPS. Therefore, it is recommended practice that both the input circuit to the UPS and the associated UPS bypass circuits (including the manual maintenance bypass circuit) be equipped with effective Category “B” SPD, as specified in IEEE Std C62.41.
TPD Comment: IEEE recommends protecting power feeding uninterruptible power supplies. Even if the UPS has all mode surge suppression built into it (check the UPS specifications) and is designed to provide good surge protection and filtering to the equipment it is feeding, it can’t adequately protect itself from lightning and other large transients. A stronger SPD installed on the electrical panel directly feeding the UPS protects not only the UPS but also all other equipment (including light bulbs, ballasts, and LEDs) fed from the protected panel. If equipment is important enough to be fed by a UPS, it is important enough to be protected by a quality all mode surge suppressor with enhanced filtering.
8.6.6 Data/communication/telecommunication systmes surge suppression
Electronic equipment containing both ac power and data cabling should also be properly protected via SPDs on both the ac power and data cables…
TPD Comment: IEEE recommends the proper use of data surge protection along with power protection. Since both AC and data is running to the equipment, the potential for ground loop problems exists. TPD provides design drawings showing the recommended points to install the suppressors and the recommended ways to ground the suppressors which help reduce the potential for ground loops, also known as current loops.