Frequently Asked Questions
Short guide to SPD applications
What do the terms surge protection devices, surge protection cabinet, line protection device, line protection unit, and line protection circuit board mean?
As practitioners who use the existing communications equipment and computers in security and communications systems, we often hear about surge protection devices, surge protection cabinets, line protection devices, line protection units, and line protection circuit boards.
From this list, many have a notion of lightning arresters because they have come across lightning protection in Power Supply projects in Grounding and Lightning Protection section. In general, a movie Going inside a Thunderstorm – and even just its title – comes to mind.
Why is the knowledge of lightning arresters and surge protection necessary and who needs it?
Serious customers in the field of communications and security systems, including public contracting authorities, begin to establish the SPD requirement in their terms of reference for tenders on multi-million civil and industrial construction projects. Consequently, professionals who have been designing security and communications systems for many years have to become familiar with this discipline in a prompt manner in order to win contracts and successfully implement integrated security system, communications system, PA/GA and area warning system, automatic fire protection system and fire alarm projects and their subclasses.
There is generally a lack of time to approach this subject because more serious problems need to be solved to implement a project, and SPDs are handled by a residual principle – let the companies select everything using a checklist. But the checklists are often standard and pass from tender to tender together with TOR as carbon copies. It is generally not bad: the service becomes a standard one, but thunderstorms and induced noises are different, so a project manager shall preferably understand what he/she is using and why. And above all – equivalents, as it happens in our job.
Let’s make an unpretending attempt to address the subject from the perspective of application of these products, rather than from the point of view of a supplier and designer.
What is SPD?
Why are SPDs/LPDs required?
Why are surge protection devices and lightning arresters required?
When systems are installed, there is a risk of their failure due to various causes::
1. Ageing and internal causes (unreliable hardware components, workmanship defects, misuse – failure to follow temperature and power supply conditions, wrong equipment application for projects)
2. Failure as a result of thunderstorm, lightning strike both in an object itself (building, line structure) and in the closest area (adjacent object, tree)
3. Failure due to electromagnetic interference caused by other operating equipment, e.g. power machines with starters.
Impacts from Sections 2 and 3 cause surge overvoltage in communications network equipment (even in power equipment, e.g. lighting fixtures). The term has been introduced by standards and, hence, it has been included in the names of devices: SPD – surge protection device. Other, more concise, terms are also known: a lightning arrester and a protection device…
Thus, SPD is a type of a protection device, together with thermal protection, power overloading protection, interference protection and many other protection systems for radio and electronic facilities.
SPD is designed to prevent the failure of the equipment protected by SPD.
It is clear that the operation of the protected equipment during protection may be interrupted (loss of communication/data exchange and lighting), but when the impact has disappeared, the equipment is still functioning, e.g. the system can be restarted with a high degree of probability.
In other cases, the Customer is not yet aware that SPDs are needed, and then, being a professional (designer, project manager or installer), we shall offer protection of the Customer’s millions against lightning, thunderstorm, welding, high-voltage power lines and electronic warfare system exercises which are accidental yet predictable in this day and age. The price paid is equal to thousands of rubles, but there is a possibility to avoid any damage of a sophisticated system and loss of valuable data, and what is more – to avoid loss of money and system performance.
How are SPDs classified by the types of tests? How does this knowledge allow protecting power lines?
How does the SPD test class allow designing power protection against lightning?
There are very interesting physical models of a lightning strike in a building and near zone for lightning diverter selection, e.g. inscribed sphere theory.
SPD classification and testing specifications are based on lightning protection and its theoretical modeling. This classification is described in standards, but the essence should be known:
- • When SPD has not been tested, or has 2 to 4 rather than 8 to 20 parameters clearly stated, you cannot even say that it ensures any protection.
- • There are 3 test classes for SPDs, and SPDs are conditionally divided into several testing groups; moreover, SPDs may correspond to two or even tree classes at once (just like summer, winter and all-weather tires).
So, when an “all-weather” SPD is offered, you shall grow suspicious.
More simply, the SPD test classes described in standards may be defined as follows.
Class 1 – testing simulates direct lightning strike in the object on which the protected equipment is installed. For example, lightning strikes an antenna mast or a building where power cables enter. In this case, antennas (presumably active ones) or a main distribution board will be able to protect only SPDs which have undergone (comply with) Class 1 testing.
Class 2 – testing simulates either impact on downstream equipment (downstream of the main distribution board) or less strong induced secondary impact of lightning on the equipment in a zone away from the lightning strike point, e.g. in an adjacent building. In case of an antenna, it simulates a strike in an adjacent mast with a lightning diverter and grounding.
Class 1 and 2 tests are usually focused on SPDs which protect power supply circuits. Why should it be power supply circuits, because, in other words, they are more resistant and have no components sensitive to 5 V. This is a complicated topic which requires this publication to be read from beginning to end.
Class 1 – Testing of SPDs for power circuit breakers and cables from transformer substations, when a load receives 220 V/380 V from 5…20 kV upstream of the main distribution board of a building/facility.
Class 2 – Testing of SPDs to be installed in power distribution boards inside a facility downstream of the main distribution board. SPDs tested according to Class 1 and 2 protect mainly power circuit breakers with operating voltages up to 1,000 V. Certainly, the test parameters included in the standards are only an average lightning impact model. However, it is declared that the selected test pulse parameters (power, current, voltage, wavefront times, duration) correspond to the impact from a real lightning and have been obtained during multiple measurements. We cannot check this, so we take this for granted.
Class 3 – Testing of SPDs protecting terminal equipment, such as display units, servers and switchboards. These are any equipment and cable lines, located within a facility and energized via a distribution board.
Such classification initially allowed somehow arranging SPDs, together with power controls: circuit breakers, residual-current circuit-breakers, residual current operated circuit-breakers with integral overcurrent protection, etc. Equipment protection algorithms have emerged: Class 1 SPDs at the main distribution board input, then Class 2 SPDs on panelboards, and Class 3 SPDs directly on communication cabinet terminal boards. These algorithms made it possible to protect power lines and supply “protected” power, free of hazardous induced voltages, to a consumer.
How SPDs are used in server- and Ethernet/IP-based security and communications systems?
By now, server- and Ethernet/IP-based distributed digital low current systems have been used most frequently. Self-supporting systems such as dispatch control, access control, fire alarm and other systems use their own low-level and medium-level communications protocols, but eventually during integration with other systems, conversion into Ethernet and local network access take place. High data exchange rates (up to 10 Gbit), standard communications protocols and widespread use are unmatched advantages of IP transmission.
For professionals, there is no need to describe the structure of virtually any current security and communications system. Certainly, expensive server hardware is a necessary system component (except for small systems), which is installed in cabinets or racks according to current standards and has a standard structure:
- one or more servers;
- passive switching facilities (copper and optical panels with sets of patchcords – connecting cables), requiring no power supply;
- storage in the form of separate disk array units which are sometimes integrated into server housings
- data transmission network equipment, or active networking equipment (switchboards, media converters, routers, modems, access points and transceivers). It should be noted that a part of active networking equipment may be excluded from the server rack and placed outside the building (e.g., in communication stations on perimeter)
- uninterruptible power supply equipment, APS, the most heavy-weight portion of the rack including the batteries, the rack-mount power circuit breaker panel to control the field equipment power supply (servers, switchboards and terminal equipment distributed over the facility: sensors, video cameras, actuating devices and dispatch controls)
Low current system structure, requirements for the rack and the cabinet, APS, IP standards, including PoE, are described in detail in TOR for tender and prevent the designer and installer from any improvisation by deviating to analogue equipment and similar options. In this case, the designer shall select from domestic equivalent options (if any), strictly follow the TOR requirements and offer competitive advantages, such as increased reliability (survivability) of packages and systems, to the Customer.
SPD ensures system resistance to various shock impacts, such as thunderstorm, lightning strike in the facility, industrial electromagnetic radiation surges, which cause so called surge overvoltage.
The TOR for digital low current system design, design itself, purchase lot, and checklist often contain a reference to lightning protection, lightning arresters, SPD, a surge protection cabinet, and a line protection device. Again we face a SPD selection problem. In other cases, the Customer is not yet aware that SPDs are needed, and then, being a professional (designer or installer), we shall offer protection of the Customer’s millions against lightning, thunderstorm, welding, high-voltage power lines and electronic warfare system exercises which are accidental yet predictable in this day and age. The price paid is equal to thousands of rubles, but there is a possibility to avoid any damage of a sophisticated system and loss of valuable data, and, what is more, to avoid loss of money and system performance.
What kind of problems arise during IP equipment protection?
Since the early 21st century may be easily called the age of Internet, then IP devices have had full market coverage and therefore are in great demand. IP equipment is protected by Ethernet port/PoE line protection devices UZL-E/EP and similar devices which have multiple markings and names. Such abundance often makes it difficult to find a required product in a browser. However, a professional may choose the right product by reading our dummy course and without sending the checklists. It will be an informed choice, which is always pleasant.
For better understanding of Ethernet equipment protection, the following shall be learnt:
- what is the difference between common-mode interference and reverse-phase interference or differential-mode interference?
- what is PoE and its trick, why does it assume various shapes?
- what are UTP cable categories and what is the difference between Category 5 and Category 5-E or 6?
- why shall we know SPD attenuation and what is it?
We shall not refer the businessman to GOST or make any footnotes with numbers as in War and Peace by Leo Tolstoy, a book which has been hardly read from beginning to end by anyone but the author himself. Let’s use the Latin aphorism: “Eschew obfuscation, espouse elucidation”.
How is IP system protection arranged?
Staged protection of equipment power circuits is described in SPD Classification section. According to this, server rack or cabinet or switchboard power protection is provided by means of inclusion of a power line protection device UZP-220, or several UZP-220, if there are more than one power input from the mains, at the cabinet input. Besides, at the Power Supply (Electrical) stage, a Class 2 SPD-220 shall be added to the server building distribution board and a Class 1 SPD (two SPDs, if there are two entries – a primary and a backup one) – to the main distribution board at the cable entry into the server building..
And now a more complicated stage follows.
What is the algorithm of SPD selection for Ethernet ports?
How do you define the SPD locations and number?
How do you choose a SPD design package for Ethernet equipment protection?
Для выбора УЗИП, работающих по портам Ethernet оборудования, надо определиться с местом их установки. Самый простой вариант- сразу после патч-панели, куда приходят «медные линии» – кабели UTP/FTP. Если медных панелей нет, то входные кабели обжимаем RJ-45 и включаем в панель УЗИПов, например в рековом исполнении (БЗЛ-ЕП16).
To choose SPDs for Ethernet ports, define SPD installation points. The simplest option is immediately downstream of the patchboard where copper lines – UTP/FTP cables – come to. If there are no any copper boards, then crimp the cables using RJ-45 and connect them to the SPD panel, e.g. rack-mount one (BZL-ЕP16).
It is important to ensure that the SPD unit is grounded via the rack/cabinet and the cabinet is grounded to the main grounding bus on the main distribution board, or ground the cabinet to protective earthing (PE) pin in the server room. Besides, the earthing issues shall be always solved at the Power Supply stage regardless of SPD. (Like in the comedy movie You’re Kidding!: “it will cost nothing to you”). For outdoor switchboards designed as communications cabinets, it is allowed to use single SPDs which are installed at the copper line input and output in the cabinet.
For terminal equipment, such as outdoor video cameras in sealed boxes (temperature-proof housings) or expensive SPEED-DOMEs (high-speed PTZ cameras), PZL-EP unpacked board shall be preferably installed directly in the video camera box/housing or in the junction box which is always available for connection of sealed outdoor cameras. In other words, ideally, any Ethernet line section (except for a fiber-optic line) shall be terminated using UZL-E/ЕP. Each SPD shall be grounded to the cabinet, and the cabinet shall be also grounded preferably locally, i.e. directly on the route. For example, using a pin – quickly and reliably (ZVS-3 vertical earth rod ).
For simplicity, imagine a lightning and estimate where it will be discharged. If as a result of search for ground the lightning goes to a “mother-in-law” and is grounded there, the “mother-in-law” will have bad luck.
So, when the SPDs are in their places and their number is known, we only have to choose their type. Now we know how many SPDs are required, their design, and where they are to be installed.
Three main designs for a low current system with Ethernet copper lines:
- Rack-mount group SPDs for server room cabinets and racks – BZL-EP 8(16) and equivalent.
- Single packaged SPDs for DIN rail mounting in thermal insulated cabinets – UZL-EP and equivalent
- Unpacked SPD for mounting in boxes or junction boxes for terminal IP equipment – PZL-EP and equivalent
How can be SPD chosen by the type of “copper”?
Let’s proceed to the selection of the SPD type by the type of UTP cables.
If you have an Ethernet port, but you don’t know exactly its capacity and you need to choose SPD, you’d better use a UTP cable category as reference. Usually, system equipment such as switchboards may be eventually replaced with, for example, high-speed equipment; on the other hand, cables and other low voltage cabling components (cable ducts, trays, etc.) remain unchanged. Therefore, if you know the cable category, you know its maximum transmission rate. Then you need not replace SPD during the next system upgrade.
Currently, local Ethernet networks (LAN) may have data rates up to 10…10,000 Mbit/s with various UTP/FTP cable categories corresponding to them.
What are UTP cable categories and what is the difference between Category 5 and Category 5-E or 6?
Most of the systems use Category 5E and 6 cables. These cables have transmission rates up to 1,000 Mbit/s.
Currently used cables are summarized below:
Category 5 (bandwidth 100 MHz) – 4-pair cable used to install 100BASE-TX local area networks and telephone lines, supports transmission rates up to 100 Mbit/s using 2 pairs.
- Category 5e (bandwidth 125 MHz) – 4-pair cable, enhanced Category 5. Transmission rate up to 100 Mbit/s using 2 pairs and up to 1,000 Mbit/s using 4 pairs. Category 5e cable is the most common and is used to install computer networks.
- Category 6 (bandwidth 250 MHz) – used in Fast Ethernet and Gigabit Ethernet networks, has 4 conductor pairs and transmission rate up to 1,000 Mbit/s. It was added to the standard in June 2002.
- Category 6a (bandwidth 500 MHz) – used in Ethernet networks, has 4 conductor pairs and transmission rate up to 10 Gbit/s, will be used for applications with bit rates up to 40 Gbit/s. It was added to the standard in February 2008.
As for UTP/FTP types, it doesn’t matter for us, this is about kinds, materials, shielded/unshielded, shielding methods – dual-shielded or completely shielded. Generally, UTP cable Cat. 5E, up to 1000 Mbit/s, unshielded, is the right one. It is cheap and mainly allows solving all issues. For 10 Gbit/s rates, fiber optics appears to be more preferable, but it does not require SPD.
- For video cameras, 10/100 Mbit/s is sufficient.
- For switchboards, field switchboard cabinets and switchboard input ports in the server room from the field, transmission rate up to 1,000 Mbit/s is basically sufficient.
- For connections between servers and storages, rates up to 1,000-10,000 Mbit/s are required (Category 5E and 6A cables).
Data transmission rate is the basic parameter for Ethernet SPD.
Why shall we know SPD attenuation and what is it?
There are some more important parameters: Insertion loss (insertion attenuation) at a certain frequency. If no loss has been found, then it is an open question whether the line protection device will work at the specified rates, and how stable it will work.
if it is of any interest, attenuation for rates up to 100 Mbit/s is specified at 100 MHz band edge, for rates up to 1000 Mbit/s – at 250 MHz .band edge. For example, UZL-EP has attenuation <2 dB at up to 250 MHz.
Conclusion: always check the SPD transmission rate for compatibility with the equipment to be protected.
How do you choose SPD for PoE ports?
What is PoE and its trick, why does it assume various shapes?
PoE is an Ethernet derivation and often brings to a nonplus. Even though we have finally studied the question, we will forget everything in a month. Generally, daemons in Linux immediately come to mind (for those who know). .Let’s get this over with, and with UTP/FTP categories too.
The problem is that field equipment is more often energized via PoE. This allows to avoid additional cabling and to simplify the diagrams and documents.
What kinds of PoE standards exist?
There are several PoE standards of which you shall be aware. The following may be specified in the field equipment datasheet: PPoE, PoE, PoE+, Hi PoE, 802.3af, 802.3at Class 0, 1, 2, 3, 4, or anything from this list in various combinations. SPD descriptions at the manufacturers’ web sites may include anything from this list, but in another combination. In this case, it is hard to be sure that the product is suitable for you. The only way out is to try to understand this.
What’s the difference between the standards?
In a nutshell:
- different powers from 4.5 W to 30 W are supplied
- different conductor pairs are used for power supply
- power is supplied for different maximum cable lengths
- connections with power supply
It is clear from the above that PoE is many-faced and it needs to be handled with care.
How is PoE port protection arranged?
For SPD selection, it is important that the pairs which simultaneously transmit power and data are protected against disruptive induced voltages both by the signal (data stream) voltage level and power supply voltage level.
The PoE voltage is up to 57 V and the signal voltage is up to 5 V (!). Thus, if 10 V is induced to the signal carrying input (port contact pairs), then the port will be damaged, therefore the SPD shall limit the induced voltage to 6 V. However, if the SPD reduces the voltage to 6 V everywhere, it will successfully short circuit the PoE, and then the PoE source will cut off power supply. Therefore, UZL-EP is not just an overvoltage/overcurrent limiter, but is linked to RJ-45 wiring termination options.
In order to proceed, we need to address the following question finally:
What is the difference between common-mode interference and reverse-phase interference or differential-mode interference?
Ethernet technology has inherited the best at the physical layer from analogue twisted pair transmission – high immunity to common-mode interference.
When two wires are twisted into a pair, as in UTP, any induced voltage influences each wire virtually in the same manner and generates induced current in it. Currents flow in the same directions, and induced voltages occur on the wire length at the location where the cable is connected to the equipment (e.g. switchboard) input – this is common-mode interference. But luckily, when there are 2 similar voltages, they may be deducted at the differential amplifier input and get no induced voltages. And one desired pulse (0/1 stream pulses) at the transmitting side, e.g. IP camera, will be sent directly and the second pulse will be inverted to ground (shield). As a result, the desired pulse will be doubled by voltage at the differential amplifier input. That’s the catch. Therefore, ordinary induced interferences are controlled using this method.
But a twisted pair will never overcome differential-mode or reverse-phase interference. And where would it come from outside, if the wires are twisted? And the worst thing is that the differential amplifier inputs themselves will be damaged by the high voltage, and there will be nobody to deduct. However, there is nothing ideal in the world. Therefore, in case of lightning strike or high induced voltage, conductors will generate induced current in a slightly different way, and slightly different induced voltages will occur at the differential amplifier input. It is obvious that the stronger the external impact the larger the delta. This is the first. So, the differential amplifier input shall be protected with our line protection device.
How does it work or which is the main operating principle of PoE devices?
The main principle of PoE is as follows:
- data (sequences 0 and 1, stream) – the difference of potentials in a wire pair
- power supply – the difference of potentials between wire pairs
There are 4 main types of PoE power supply: two for 10/100 Mbit/s standard and two for 1,000 Mbit/s standard. And since 1,000 Mbit/s standard has a higher rate, all 4 pairs (A, B, C, D) are used for transmission (that’s why the transmission rate in a pair is still equal to 250 Mbit/s and the bandwidth is not increased and remains equal to 250 MHz). For 10/100 Mbit/s standard, only 2 pairs are sued for transmission with one twisted pair used only for transmission and the other one used only for receipt (it is obvious that therefore the transmission rate in each twisted pair is two times lower, and since the data exchange is more simple, then the rate is 2.5 times lower as compared with 250 Mbit/s, i.e. finally we obtain our 100 Mbit/s and 100 MHz bandwidth, respectively.)
That is all.
Since PoE is more often used for field equipment up to 100 Mbit/s, two main port supply methods exist
Option (method) A – simultaneous power and data transmission via the same signal wires.
Both electric power and data are supplied via wires 1, 2, 3, and 6. High-frequency transformers with central tap from secondary windings are used both on the transmitter and receiver sides.
Option (method) B – simultaneous power and data transmission via different wires.
Wires 4, 5, 7, and 8 are used for power supply. The other wires are used for data transmission (option B)
For 1,000 Mbit/s options, power is supplied via the same twisted pairs according to the same options A and B, but the main thing is that all twisted pairs are engaged for data transmission. No figures are provided. This is almost the end.
What is the SPD circuit for Ethernet with (and without) PoE?
What is the SPD circuit for Ethernet with (and without) PoE?
So, from the PoE power supply arrangement we have:
- data (sequences 0 and 1, stream) – the difference of potentials in a wire pair up to 5V (pulses up to 250 MHz)
- power supply – the difference of potentials between wire pairs up to 57V DC.
These circuits shall be protected. For a typical circuit of UZL-EP, see any datasheet at the web site (UZL-EP, PZL-EP, BZL-EP).
Generally, the “right” SPD for Ethernet with PoE shall contain three “defense” lines:
- three-pin gas discharge tubes for high input overvoltage between the pair wires (4 in total) and ground (PE) for pick-up voltage of about 150 V,
- suppressors or TVS diodes for quick response at 60 V and higher between the power twisted pairs (x2 by the number of supply methods A and B)
- limiting assemblies with TVS diodes for quick response at 6 V between the twisted pair wires (inside the twisted pair) (X4 by the number of pairs).
None of the devices will be addressed herein; there are detailed descriptions in other publications. It is important to understand what we shall protect and why we need 3 stages. Gas discharge tubes ensure “slow” (100 ns) but powerful protection, and the response rate up to 10 nanoseconds is provided by TVS diodes. Limiting assemblies with TVS diodes manage to protect sensitive inputs of the differential amplifier of the port.
In this case, frequency characteristics are directly associated with the transmission rates.
It is obvious that without PoE there is no need to maintain power supply at +57 V, and the protection stage between the twisted pairs for 60 V is avoided (UZL-E).
For now, this is the end of our dummy course.