Transient overvoltage protection to IET wiring regulations 17th edition (BS 7671:2008+A1:2001) - Furse - 2015

Application Note Transient overvoltage protection to IET wiring regulations 17th edition (BS 7671:2008+A1:2001)

2 FTOP16715 | Transient Overvoltage Protection The latest amendment to the IETWiring Regulations 17th Edition(BS 7671) brings into sharp focus theneed to protect sensitive and criticalelectronic systems against transientovervoltages (surges). Amendment 1 of BS 7671, effective from 1st January 2012, requires all electrical system designs and installations to be assessed against risk of transient overvoltages of atmospheric origin, or from switching events, in line with its Sections 443 & 534. Section 443 defines the criteria for riskassessment, whereas Section 534 describes the selection and installation of suitable Surge Protective Devices (SPDs), where required, for effective transient overvoltage protection. Whilst concerned with protection of ACpower supplies, BS 7671 does make clear the need to protect all incoming/outgoing metallic service lines, including data, signal and telecoms lines, following BS EN 62305. Why is transient overvoltage protection so important? Transient overvoltages are short duration surges in voltage between two or more conductors (L-PE, L-N or N-PE), which can reach up to 6 kV on 230 Vac power lines, and generally result from:   – Atmospheric origin (lightning activity  through resistive or inductive    coupling  (see Figures 1 & 2), and/or   – Electrical switching of inductive  loads Transient overvoltages significantly damage and degrade electronic systems. Outright damage to sensitive electronicsystems, such as computers etc, occurs when transient overvoltages between L-PE or N-PE exceed the withstand voltage of the electrical equipment (i.e. above 1.5 kV for Category I equipment to BS 7671 Tables 44.3 & 44.4). Equipment damage leads to unexpectedfailures and expensive downtime, or risk of fire/electric shock due to flashover, ifinsulation breaks down. Transient overvoltage protection Degradation of electronic systems, however, begins at much lower overvoltage levels and can cause data losses, intermittent outages and shorter equipment lifetimes (see Figure 3). Where continuous operation of electronic systems is critical, for example in hospitals, banking and most public services, degradation must be avoided by ensuring these transientovervoltages, which occur between L-N, are limited below the impulse immunity of equipment. This can be calculated as twice the peak operating voltage of the electrical system, if unknown (i.e. approximately 715 V for 230 V systems). Protection against transient overvoltages can be achieved through installation of a coordinated set of SPDs at appropriate points in the electrical system, in line with BS 7671 Section 534 and the guidance provided in this publication. Selecting SPDs with lower (i.e. better) voltage protection levels (Up) is a critical factor, especially where continuous usage of electronic equipment is essential. 1.5 kV (L-PE/N-PE) 2x peak operating voltage(e.g. 715 V L-N) Nominal system voltage (e.g. 230 V) Safe  Operating  Area Degradation DAMAGE Safe Operating Area Degradation Degradation DAMAGE DAMAGE Figure 1: Resistive coupling Resistively coupled transients are caused by differences in potential between two connected earths. Energy from ground strikes flows away through the path of least resistance, and increases the potential in local earths, cabling and electronic circuitry. Where these are linked to separate earths by a metallicservice line, the potential is shared, creating transientovervoltages as the current attempts to flow. Figure 2: Inductive coupling Inductively coupled transients are caused by electromagnetic pick-up. A lightning discharge gives rise to an electromagnetic field. If metallic services, such as overhead power lines, pass through this field a voltage will be picked up by, or induced on to, the line. Figure 3: Equipment risk Degradation of electronic systems begins at lowertransient overvoltage levels and affects criticalelectronic systems whenever the impulse immunity of the equipment is compromised. Damage occurs when a transient overvoltage exceeds the withstand voltage of electrical and electronic equipment.

Transient Overvoltage Protection | FTOP16715 3 Sections 443 and 534 of BS 7671 covertransient overvoltage risk and SPDselection/installation on AC power supplies. Determining risk to BS 7671BS 7671 Section 443 establishes that protection against transient overvoltages is required in an installation which includes a structural lightningprotection system (LPS), and/or connected metallic service lines at risk from lightning. It details protection requirements forAC power lines, and refers to BS EN 62305 regarding additional metallic service lines (data,signal & telecoms). Protection is required where:   – The expected transient overvoltages   would exceed the withstand  voltage1 of installed equipment (as defined byTables 44.3 & 44.4 of BS 7671), and   – The risk of consequential loss (to  life,property or provision of service) is deemed unacceptable (443.2.4) If terminal equipment to Category I of Table 44.3, such as computers/laptops etc., is to be connected to the fixed electrical installation, it must be protected against transient overvoltages (Table 44.4). The flowchart below (Figure 4) definesrisk assessment in terms of potentialconsequential losses. Note, as per the flowchart, risk ofconsequential loss to human life, publicservices or to commercial/industrial activity always results in the need to install protection measures (443.2.4 Note 2). Following this process, where the need for protection is established, BS 7671 requires the selection and installation of SPDs on the AC power supply in accordance with its Section 534. Figure 4: Transient overvoltage risk assessment to BS 7671 Note, withstand voltage protects only against failure of equipment. For continuous operation of critical equipment, impulse immunity must be protected. Overhead line supplying the building at risk of direct strike - see BS EN 62305 (443.1.1) Install lightning current TYPE 1 SPD or combined TYPE 1+2 SPD on main distribution board to prevent dangerous flashover (534.2.1) Protection against transient overvoltages not required (443.2.1, 443.2.2) if equipment withstand voltage 1 to Table 44.3 Protection against transient overvoltages not required if equipment withstand voltage 1 to Table 44.3 Risk of direct lightning  (BS EN 62305) or lightning protection system installed? (443.1.1) Installation presents higher risk  (e.g. fire) or requires higher reliability from transient overvoltages,  including electrical switching  (443.2.2 Note) - see BS EN 62305 Consequences related to human life, e.g. safety/medical equipment? (443.2.4) Consequences related to loss of public service, e.g. IT centres and museums? (443.2.4) Consequences related to loss of commercial activity, e.g. hotels, banks, farms?  (443.2.4) Consequences related to individuals or groups, e.g. residential buildings? (443.2.4) ALTERNATIVE simplified risk assessment  (443.2.4).  Check if data, signal and telecoms lines require protection (443.1, 534.2.1) NO START YES YES NO NO NO NO NO YES YES YES YES YES Consider following levels of consequences from transient overvoltages, including electric switching Install coordinated set of  transient overvoltage SPDs for equipment protection (e.g. TYPE 2 or Combined TYPE 2+3)  on distribution boards feeding sensitive electronic  equipment (534.2.6) Transient overvoltage protection Risk assessment

4 FTOP16715 | Transient Overvoltage Protection Transient overvoltage protection SPD selection & installation ESP 415/I/TNS L1 N Enhanced Mains Protector 250 AgL If RED replace limp = 25kA/mode lmax = 100kA/mode ln = 25kA/mode Uc = 320VAC Up 1.4kV Ures(limp) 1.3kV L2 L3 PE Enhanced Mains Protector EN/IEC 61643 PATENT APPLIED FOR L L' L2 L2' L3 L3' N N' 11 14 12 STATUS PE OCPD OCPD Main earthing terminal OCPD OCPD : Overcurrent protective device (fuse) ESP 415 D1/LCD with Type 2performance installed at sub-distribution protects fixedequipment on the electricalinstallation against transientovervoltages. ESP 415/I/TNS with Type 1performance installed atservice entrance to diverthigh energy lightningcurrents to earth, and remove risk of flashover. Combined Type 2+3performance of the SPDinstalled at sub-distributionprotects downstreamsensitive equipment againsttransient overvoltages. Plug-in ESP MC with Type 3performance protects criticalequipment at local levelagainst switching transients. Line length 10 m Service entrance/ Main distribution board Fixed equipment (e.g. UPS) Critical equipment (e.g. hospitalequipment) Risk ofswitchingtransient ESP 415 D1/LCD Full ModeType 1+2+3 SPD ESP 415/I/TNSType 1+2 SPD Sub-distribution board Terminal equipment Line length 10 m L1 L2 L3 N L1 L2 L3 N PE PEN Figure 5: Typical installation on a 230/400 V TN-C-S/TN-S system using Furse SPDs, to meet the requirements of BS 7671 Assessing installation requirements BS 7671 Section 534 focuses guidance on selection and installation of SPDs to limit transient overvoltages on the AC power supply. Section 443 states that 'transient overvoltages transmitted by the supply distribution system are not significantly attenuated downstream in most installations' (443.1.1 NOTE 3). BS 7671 Section 534 therefore recommends that SPDs are installed at key locations in the electrical system:   – As close as practicable to the origin  of the installation (usually in the main distribution board after the meter) (534.2.1)   – As close as practicable to sensitive   equipment (sub-distribution level),     and local to critical equipment    (534.2.1 Figure 5 shows a typical installation on a230/400 V TN-C-S/TN-S system using Furse SPDs, to meet the requirements of BS 7671. The illustration demonstrates how effective protection comprises a service entrance SPD to divert high energy lightning currents to earth, followed by downstream SPDs at appropriate points to protect sensitive and critical equipment. Transient overvoltage SPDs (Type 2 and Type 3, or Combined Type 1+2+3 and Type 2+3) should therefore be installed downstream of the service entrance. These SPDs further protect against those transient overvoltages caused by indirect lightning (via resistive or inductive coupling) and electrical switching of inductive loads. Combined Type SPDs (such as the Furse ESP D1 Series and ESP M1/M2/M4 Series) significantly simplify the SPD selection process, whether installing at the service entrance or downstream in the electrical system.  These SPDs, classed as enhanced SPDs to BS EN 62305, offer technical and economic advantages over standard SPDs, providing:   – Combined equipotential bonding and    transient overvoltage protection   (Type 1+2 & Type 1+2+3)   – Full mode (common and differential    mode) protection, essential to safe    guard sensitive electronic equipment     from all types of transient overvolt    age - lightning & switching (524.2.2     NOTE 1), and   – Effective SPD coordination within a  single unit versus installation of multiple standard Type SPDs to protect terminal equipment Selecting appropriate SPDs SPDs are classified by Type withinBS 7671 (534.2.1), following the criteria established in BS EN/IEC 62305. Where a building includes a structural LPS, or connected overhead metallic services at risk from a direct lightning strike, equipotential bonding SPDs (Type 1 or Combined Type 1+2) must be installed at the service entrance, toremove risk of flashover (534.2.3.4.2). Installation of Type 1 SPDs alone however does not provide protection to electronic systems (534.2.1 NOTE 3).

Transient overvoltage protection Protection for 230/400 V TN-S or TN-C-S supplies L N T2 C T1 Iimp 4kAIn 20kA Imax oc 40kA U 6kV c z ac U 280V  47-63H B D T3 125 AgL ! GREEN FULL PROTECTIONGREEN & RED REDUCED PROTECTION (replace unit) RED NO PROTECTION WARNING: If lit /  flashing disconnect unit & check Neutral to Earth voltage EN/IEC 61643 PATENT APPLIED FOR STATUS INDICATION ESP 240D1 L L 1 N 1 N 11 14 12 STATUS STATUS A OCPD OCPD SPD 0.25 m 0.25 m Main earthingterminal orconnectingconductor bar Figure 6: Critical length of connecting conductors (534.2.9) SPD connections should be kept as short as possible ideally below 0.25 m between SPD, live conductors & earth,but in any case not more than 0.5 m, to reduce risk of additive inductive voltage drops across the conductors. IMPORTANT: Equipment is ONLY protected against transient overvoltages if all incoming / outgoing mains and data lines have protection fitted.  Data/ Telecom Power SPD performance The most important parameter for SPD performance is its voltage pro-tection level (Up) (534.2.3.1.1) and not its energy withstand (e.g. Iimp) (Fig 16A.5). The lower the voltage protection level (Up), the better the protection afforded to the withstand voltage or impulse im-munity of the equipment (534.2.3.1.1). Equally, short connecting leads between the SPD and conductors are paramount to keep transient overvoltages to a mini-mum (see Figure 6).Controlled installation to BS 7671 of SPDs with lower (better) voltage protec-tion levels (Up), and short connecting leads optimises protection at terminal equipment by: SPD coordination Smaller installations may require onlya single SPD (534.2.2). However where the protective distancebetween SPD and electrical equipmentexceeds 10 m, additional downstream SPDs may be needed to counter voltage oscillations (534.2.3.1.1). SPDs installed on the same conductor should coordinate with each other to ensure effective, continuous protection (534.2.1 & 534.2.3.6). The selection chart (right) defines the appropriate Furse SPDs to achieve coordination on a 230/400 V TN-S or TN-C-S system, dependent on installation requirement, in line with BS 7671.For TT systems, contact Furse. All Furse SPD sets for power and data lines are specifically designed to ensure coordination. Following BS 7671, installation of Furse SPDs at service entrance, sub-distribution and at critical electrical equipment, will ensure optimal, consistent protection against transient overvoltages. Protect additional metallic services BS 7671 is focused towards protection of AC power supplies. For protection measures against directlightning strikes, and against transientovervoltages on additional metallic service lines (e.g. data, signal & telecoms), BS 7671 refers to BS EN 62305 (534.1 NOTE 2).   – Limiting additive inductive voltages on the SPD’s connecting leads   – Reducing risk of downstream volt-age oscillations which can reach up to twice the SPD’s Up and cause damage at equipment (534.2.3.1.2) Furse SPDs are designed with industry leading low voltage protection levels (Up), and many include a remote display option to ensure SPD positioning as close as possible to conductors. Full protection of electronic systems can only be achieved if all incoming/outgoing metallic services, including data, signal and telecoms lines are protected. Transient Overvoltage Protection | FTOP16715 5

6 FTOP16715 | Transient Overvoltage Protection Standard Part No. Remote DisplayOption Part No. 1 Weatherproofenclosure 2 SPD Performance Statusindication ESP 415/I/TNSESP 415/III/TNS  ESP 415 M4ESP 415 M2 ESP 415 D1 ESP 415 D1/LCD ESP 415 M1  ESP 240 D1 ESP 240 M1 ESP MC -- ESP 415 M4R ESP 415 M2R ESP 415 D1R  ESP 415 D1R/LCD ESP 415 M1R --- WBX D4WBX D4 WBX M4WBX M2WBX D8 WBX D8WBX 4 WBX D4WBX 3- Combined Type 1+2Combined Type 1+2 Combined Type 1+2+3Combined Type 1+2+3Combined Type 1+2+3 Combined Type 1+2+3Combined Type 1+2+3 Combined Type 1+2+3Combined Type 1+2+3Combined Type 2+3 LEDLED LEDLEDLED LCD 3 LED LEDLEDLED 1 Remote displays enable positioning of an SPD  close to conductors with the display mounted in  an easily visible position. 2 Weatherproof enclosures are rated to IP65 or above and enable mounting of SPDs in adverse  environments. They should be used where the  SPD is not mounted within a distribution board. 3 LCD remote display includes rotating screen text (by 90˚) for optimal positioning and viewing, as  well as audible status warning.   3 Phase 400 V1 Phase 230 V Sub-distributionboard (SDB)-located 10 m fromMDB feedingelectronicequipment Transient overvoltage protection Protection for 230/400 V TN-S or TN-C-S supplies   – No external lightning   protection system fitted   – Underground mains supply feed   – No external lightning   protection system fitted   – Exposed overhead mains   supply feed ESP 415 D1 Series ESP 415 M1 Series ESP 415 M2 Series(for electronicslocated nearMDB before SDB) For 3 Phase 400 V:ESP 415 D1 Series orESP 415 M1 Series ESP MCESP MC/TN/RJ11 (e.g. for fax machines)ESP MC/Cat-5e (e.g. for servers) 3 Phase 400 V Service entrance,after electricitymeter (Maindistributionboard (MDB) Critical terminalequipment -located 10 mfrom SDB Ground  Level Power Power Ground  Level

Transient Overvoltage Protection | FTOP16715 7   – External lightning protection   system fitted   – No. of services unknown   – External lightning protection   system fitted   – Multiple connected metallic services For 1 Phase 230 V:ESP 240 D1 Series orESP 240 M1 Series For LPL & IIESP 415/I/TNSorESP 415 M4(for electronicslocated nearMDN before SDB) ESP 415 D1 Series ESP 415 M1 Series For LPL III & IVESP 415/III/TNSorESP 415 M2(for electronicslocated nearMDN before SDB) SPD selection notes   – LPL refers to Lightning   Protection Level, as defined   by BS EN/IEC 62305.   – Voltage protection level (Up)   at the equipment terminals   should be lower than the   withstand voltage of   sensitive equipment (1.5 kV   Category I) or the impulse   immunity of critical   equipment (approx. 715 V   for 230/400 V supplies)  (534.2.3.1).   Type 3 SPD performance   applies at equipment   terminals. To BS EN 62305 an   SPD’s voltage protection level   (Up) should be no more than   600 V when tested to   BS EN 61643-11 Class III test.   All the Furse Combined Type   1+2+3 & Type 2+3 SPDs   shown in the selection chart   meet this requirement.   – All Furse SPDs shown have   been tested to at least the   minimum nominal discharge   current (Inspd) of 5 kA 8/20   waveform, for TN-S or   TN-C-S supplies as specified   by BS 7671 (534.2.3.4.1).   Note: Inspd as defined by   BS 7671 correlates with In of   BS EN/IEC 61643.   – Where a service entrance   Type 1 SPD is required, it   should be tested to   withstand lightning impulse   currents (Iimp) to   BS EN/IEC 61643.   – The value of Iimp for an   installation should be   calculated according to   BS EN 62305. Where it   cannot be calculated, the   SPD should have capability   not less than 12.5 kA per   mode to PE or common   mode (534.2.3.4.2). For more information on SPD selection, contact ABB Furse. LPS Power Data Telecom Water Gas Ground  Level LPS Power Unknown { Ground  Level Amendment 1 of BS 7671 places a clear responsibility for transient overvoltage protection on electrical system designers and installers. For many in this sphere of work, assessing the need for transient overvoltage protection will be a new requirement. Defining when and where to install SPDs can be a complex process, and sourcing the right expertise can often be as important as specifying the right product. That’s why we support our transientovervoltage solutions with CPD-accredited seminars and training, including: Transient overvoltage protectionto BS 7671 Providing key guidance on the riskassessment principles defined withinSection 443, plus selection and installation of SPDs in line with Section 534 of BS 7671:2008 (+A1:2011). Transient overvoltage protectionto BS EN 62305 Detailing the protection requirementsfor electrical and electronic systemswithin structures, in accordance withBS EN 62305-4, including the lightningprotection zone (LPZ) concept, and theapplication and coordination of SPDs.Seminars are conducted at customer premises or at our head office in Nottingham, UK.To arrange a seminar, or for more informationon protecting your installations againsttransient overvoltages, contact us directly.

© Copyright ABB 2015  9AAK10103A5594 Electronic Systems Protection Equipotential bonding and transient overvoltage surge protection Electronic Systems Protection Equipotential bonding and transient overvoltage surge protection Contact us ABB FurseUK OfficeWilford RoadNottingham  NG2 1EBTel:   +44 (0) 115 964 3700 Fax:   +44 (0) 115 986 0071  Sales Tel:   +44 (0) 333 999 9900Sales Fax: +44 (0) 333 999 9901E-Mail:   [email protected]  www.furse.com Note: We reserve the right to make technical changes or modify the contents of this document without prior notice. With regard to purchase orders, the agreed particulars shall prevail. ABB AG does not accept any responsibility whatsoever for potential errors or possible lack of information in this document. We reserve all rights in this document and in the subject matter and illustrations contained therein. Any reproduction, disclosureto third parties or utilization of its contents – in whole or in parts – is forbidden without prior written consent of ABB AG. Copyright © 2015 ABBAll rights reserved