Protect Your Infrastructure

UK Lightning Protection Standard BSEN 62305

UK Electrical Regulation BS7671 18th Edition


Surge Guidance Notes

These notes are only for general guidance and do not constitute a design, The reader should seek independent qualified advice.


  Design Guidance

Surge Protection requirements of BS7671 – IET Regulations from January 2019

& harmonisation with the Lightning protection standard BSEN 62305

BS7671 2018 Regulation 443.4

Protection against transient overvoltages shall be provided where the consequence caused by overvoltage may result in any of the following

(i) Results in serious injury to, or loss of, human life, or

(ii) Results in interruption of public services/or damage to cultural heritage, or

(iii) Results in interruption of commercial or industrial activity, or

(iv) Affects a large number of co-located individuals

BS7671 2018 Regulation 443.4.1 (revised as of Amendment. 2 – 2022)

Protection against transient overvoltages shall be provided where the consequence caused by overvoltage may result in any of the following

(i) Results in serious injury to, or loss of, human life

(ii) Results in failure of a safety service as defined in part 2

(iii) Results in significant financial or data loss

Protection against loss defined in categories (i & ii) of the above is a mandatory compliance requirement where a BSEN 62305 lightning protection system is planned or already present. Protection against loss defined in category (iii) may be equally as important to all commercial businesses, government buildings, private institutions, etc.  but must be complied with in terms of financial institutions, banks as well as data centers, emergency service providers, hospitals, etc. If a lightning protection system is not present, transient voltage protection will be necessary for category (ii) compliance and may be required for category (iii) as well.

(ii) Safety services are defined in BS7671 AMD 2, part 2 page 42.

An electrical service for electrical equipment provided to protect or warn persons in the event of a hazard or essential to their evacuation from a location

This will include but may not be limited to e.g., Fire alarm, detection, and suppression systems, smoke AOV, electric auto door access systems, designated emergency lifts, emergency lighting, telecom, emergency services auto-dial out, security systems, nurse call systems, disabled refuge systems, PA systems, interconnected safety system control, and communication networks, etc. Distribution boards supplying these systems must have differential mode SPDs installed and type III SPDs installed locally at the electronic panels.

The calculation of risks within BS7671 is now deleted and the guidebook flowchart updated. The new category definitions in amendment 2 must be complied with. The lightning protection standard BSEN 62305-2 R2 risk assessment may still be used for the coordination of SPDs. R2 risk assessment outcome results do not mitigate in any way, the need for protection against loss as defined in category (ii) part 2 page 42 of BS7671.

Regulation 443.4.2 also requires consideration for protection against overvoltages in the case of equipment likely to produce switching overvoltages or disturbances and gives conditions such as motors, inductive loads, etc (e.g., lift motors, Air Cond, etc) For all other cases (not already covered within 443.4.1, 443.4.2), protection against transient overvoltages shall be provided unless the owner of the installation declares it is not required due to any loss or damage being tolerable and they accept the risk of damage to equipment and any consequential loss. The declaration shall be in writing so that there can be no future ambiguity of responsibility for loss caused by transient surge. The written declaration should be concise and based on full expert guidance. The declaration shall NOT be used or accepted to circumvent the protection requirements of 443.4.

This departure declaration would seem only relevant for private residences without mains wired fire alarms. In Scotland however, it is now a legal requirement to have linked smoke and heat detection devices installed in all homes regardless of when these homes were built. Existing homes may be upgraded to include SPDs when installing the fire alarms; all new homes with mains wired fire systems must now have an SPD installed at the consumer unit. In accordance with 443.4 (ii)

In accordance with BS7671 443.4, designers of lightning protection systems will determine the risk factors associated with all designs under the lightning protection standard BSEN 62305 Pt 2 R1&R2 risks. From these software calculations, the outcome will drive a lightning protection design to comply with either LPL1, LPL2, LPL3, or LPL4. Each of these “Lightning Protection Levels” has specific energy characteristics and thus the surge protection device selection directly relates to these expected strike magnitudes.

LPL1 = 200KA (10/350µs Iimp)

LPL2 = 150KA (10/350µs Iimp)

LPL3&4 = 100KA (10/350µs Iimp)

From the calculated risk LPL outcome, the lightning protection designer applies a Faraday cage type system by either using the structures metal façade/roof or steel/rebar columns, or if the building is nonconductive, a series of tapes overlaid in a grid of fixed dimensions relative to the LPL design outcome. The Faraday cage conforming to BSEN 62305 dissipates 50% of the strike energy. The remaining 50% enters through the Faraday cage system into the structure via all cables entering/leaving the building. It is these cables where correct KA-rated Type1/2 surge protection measures shall be applied. i.e. LPL1 50% = 100KA, LPL3&4=50KA. All cables must be protected for compliance with BSEN 62305.

Surge protection installations shall be done in accordance with BS7671 regulation 534. This 11page long regulation provides wiring diagrams as well as connection types. 534.4.3.1 provides detail for CT1 (common mode SPDs) and 534.4.3.2 CT2 (differential mode SPDs) BS7671 Regulation 534.4.4.2 note 1 requires CT2 SPDs (e.g. 1+1, 3+1 differential mode, “Line to Neutral” protection) differential mode 1+1, 3+1 SPDs ensure continuous operation of critical equipment. BSEN 62305 R2 risk specifically refers to the prevention of loss of services. SPDs applied in an R2 risk outcome design must be CT2 (e.g. 3+1 differential mode to comply with these regulations) Specific attention is also drawn to a significant failure of internal services BSEN62305 Pt1 page 18 R1 risk “failure of internal systems where this failure may immediately endanger human life” It is important to select the correct CT2 Type2/3 surge protection measures and its necessary to install these at sub-boards which are more than 10m cable length from the previous upstream Type 1/2 device installed i.e. at the main board. (See regulation 534.4.4.2 note 1) Fire alarm and other life safety systems, ref BS7671 443.4.1 (ii)  i.e. disabled refuge, smoke vent, nurse call, etc. within a building that has a lightning system installed must also have surge protection installed at the supplying dist. boards as well as the location of these electronic panels; typically with a type III SPD where type I/II or II has been installed in the distribution board supplying the panel. Refer to BS7671 regulation 534.4.1.1: where SPDs are required

Conductive cables entering/leaving the building through the Faraday cage system are not limited to mains cables. BSEN 62305 Pt3 6.2.3/6.2.5 All conductive lines of each cable shall have surge protection measures installed as close as practically possible to the internal entry/exit position”. (Transition from internal lightning protection zone LPZ1 to external lightning protection zone LPZ0) These may include sub-boards with external circuits, Telecom systems, CCTV Cat6/Coaxial lines, Aerial/Sat dish coaxial, PV solar DC strings, Plant Control Comms, and extra-low voltage plant/equipment control lines. Lightning Protection contractors shall follow BSEN 62305 Pt 3 section 6 and BSEN 62305 Pt4. M&E contractors shall follow BS7671 regulations 443 and 534.

Incorrect selection of OCPD devices is also a major issue.  See BS7671:2018-entry 534.4.5.1. The correct backup fuses for main board service entry type 1/2 SPDs is gL/gG type. For designs where there is a lightning protection requirement LPL I/II gL/gG 250A and for LPL III/IV gL/gG 160A typically NH1 size fuses. If MCCBs are to be used, these can have a reduced current capacity of >80A (LSS prefer =>100A if possible, to enhance volt drop protection levels) With no possible statement regarding a 10/350µs lightning current with respect to breaking capacity ratings, the selected >80A breaker shall have a breaking capacity greater than the SPD capability and preferably to double the SPD 10/350µs current/line. >= 25KA breaking capacity for LPLIII/IV at 415V and >= 50KA breaking capacity for LPLI/II at 415V.  Too often installations are being incorrectly designed contrary to BS7671 534.4.5.1 and the manufacturer requirements with as little as 50-63A MCCBs/ MCB’s. These underrated OCPDs may limit the SPD protection level to as little as 5KA/line lightning current before tripping, where 12.5KA /line may be the design minimum outcome required under the risk assessed LPL III/IV and 25KA/line minimum for LPL I/II.  Breakers with underrated breaking capacity may also be damaged due to high current arcing at the contact mechanism, potentially welding the contacts shut.  Increased let-through voltage is also caused where <80A MCBs are used due to volt drop across the mechanism (REF: IEC 61643-12 TC37A table N.2) which may let through additional voltage beyond the withstand of connected equipment intended to be protected.   

Sub main boards fed with a <250A OCPD having localised external circuits (LPZ1-LPZ0) i.e. to lights, plant, outbuildings, CCTV, etc. should not be connected via <80A MCBs. In rare cases a 63A type C/D 10KA MCB may be used when there is no other option, however, this will mean potentially higher let-through voltage which may be beyond the intended equipment withstand levels resulting in damage of the equipment. Designers/installers must take this performance-limiting constraint into account as alternative solutions are available – Sub boards with external circuits which cannot accommodate an 80A MCB should have the SPD connected to the supply side of the board via a 125A isolator providing local means of isolation. Unlike a 63A MCB, this increased size of isolator will not add any significant resistance across the mechanism which may negatively affect let-through voltage, nor will an isolator trip leaving fixed and final circuit equipment open to the full exposure of the transient event. Main and sub-main board assemblies are rarely rated at less than 100A. The BS7671 explains the requirements of OCPDs.

BS7671:2018 – 534.4.5.1 states that the OCPD shall be selected to the highest permissible rating to allow the high surge current capability for the complete assembly whilst not exceeding the ratings and characteristics of the SPD manufacturer instructions for the SPD maximum overcurrent protection. These OCPD maximums are often printed on the SPD and or within the SPD data sheets. Type1 and type1/2 Lightning current, Lightning current/overvoltage SPDs are never rated for OCPD protection at less than 160A gG/gL, most state 250A gG/gL

Sub board type 2/3 transient overvoltage protection (LPZ1-LPZ2…” no external circuits) may connect the SPD via a 63A type C/D 6-10KA MCB. The SPD shall be CT2, differential mode protection L-N/N-PE (CT2, 1+1, or 3+1) configuration to protect against switching transients. Type 2 Enhanced SPDs shall have 20KA/ line transient protection (8/20µs Imax) limiting the let-through voltage (In) to 1.5Kv. CT2 (1+1, 3+1).  The maximum permissible (In) under BS7671 regulation 534.4.4.2 is 2.5Kv which allows a max. 1m total length of phase plus earth conductor

Type 1/2 service entry CT2 differential mode protection L-N/N-PE (CT2, 1+1, or 3+1) configuration shall be used where interruption/loss of critical equipment cannot be tolerated or where L-N transients may damage electronic equipment at the main panel/section board or Sub board that has any external lines LPZ1-LPZ0. CT2 configured SPDs shall be installed via two-pole SP&N or four-pole TP&N means of disconnection.

Type 2/3 SPDs are also used where there is no Lightning protection system on the structure and the mains supply feed is not via a directly connected overhead LV line. If the LV line is an overhead supply (TT), a type 1/2 SPD (3+1 or 1+1) shall be used at the main board then use type 2/3 SPDs to any other board requiring protection for internal circuit connected equipment plus external sub supply lines to i.e. garages, etc.

BS7671:2018- 534.4.8 confirms the connecting cable to the SPD shall be as short as possible and avoid loops. The total cable length is the sum of the longest length phase conductor plus the length of the earth conductor. The sum of these two lengths should be preferably no more than 0.5m and in no case greater than 1.0m.  (1.0m=1000v added to the SPD In) Enhanced SPDs shall have <1.5Kv In. to accommodate the maximum sum of 1m, Ph+E connecting length.  

BS7671 regulation 534.4.4.2 Maximum (In) is 2.5Kv. At >10M downstream circuit lengths from an enhanced T1/2 SPD connected with 1m sum of cable, may be up to twice the original (In). Installing enhanced coordinating type 2 (8/20µs) CT2 1+1/3+1 differential mode SPDs at sub-boards will reduce this possible +5Kv, down to a safe connected equipment withstand of <2.5Kv. All sub-distribution boards are rated at Uw 4KV. If left unprotected there is a high likelihood that any that are >10M from the main board SPD, may be overloaded and damage the assembly never mind the connected circuit equipment from 534.4.4.2 at 2.5KV or sensitive connected equipment at 1.5KV. It’s not acceptable under BS7671 to have these boards unprotected even if they don’t feed safety services or sensitive equipment, they still may pose a fire risk from voltage events >4Kv.

For type 1/2, 12.5KA/25KA Iimp/line SPDs the Earth cable CSA is stranded 16mm². Most SPD manufacturer’s equipment connectors are able to accommodate up to 25mm² stranded or 35mm² solid conductors. It is good engineering practice to size the Phase & Neutral conductors for the SPD installation equal to the SPD Earth conductor cross-sectional area, in this case, 16mm² as guided in BS7671 Table 54.7. This does not preclude the use of up to 35mm² conductors but should not be less than 16mm². BS7671 534.4.10 minimum cable sizes do not take into account the manufacturer’s product minimum cable size guidance which must always take precedence. See BS7671 on-site guide table 3.7.3 confirming connecting leads to be at least 16mm² for T1 –  T 1/2 SPDs. For type 2 SPDs this can be reduced to 6mm² but better to keep to 16mm² wherever possible.

BS7671:2018-{Table 54.7} allows selection (rather than calculation) of sizes for earthing and bonding conductors:

For phase conductors up to 16 mm², the protective conductor has the same size as the phase conductor.

For phase conductors from 16 mm² to 35 mm², the protective conductor must be 16 mm²

The subject of overcurrent protection of SPDs is often confusing in practice where mains power SPDs are concerned, given that the vast majority of these SPDs are installed in shunt or parallel with the supply and the installed SPD itself is therefore independent of the supply load current. The same SPD could therefore be used on a 100A supply load or a 1000A supply load and hence the cross-sectional area of the connecting leads to SPDs, therefore, does not have to be sized equivalent to the load current.

BS7671 Section 534 advises that SPD connecting cables have minimum cross-sectional areas of 16mm2 for the high energy Type 1 SPD.

Cross-sectional area values are based on the surge current that these SPD connecting leads need to carry, not the supply load current. However, in the event of a short-circuit due to say the end-of-life condition of the SPD, the connecting leads to the SPD need to be protected by a suitable OCPD.

Telecom lines shall have a minimum of 2.5KA Iimp lightning current capability/1Pr line, other lines such as Cat6 PoE, RF, Data signal lines, etc. shall have at least 1KA Iimp/line.

It is unlikely to be provided sufficient information to select the correct surge protection devices (Correct KA for LPL outcome, CT1 or CT2 connected, correct back up OCPDs) without technical discussion leading to a compliant BSEN 62305 lightning protection system installation. It is equally unlikely that BS7671 will be met in terms of regulations 443 & 534 without the input of an experienced product application specialist.

The regulations, standards, and independent guidance publications are in place to ensure risks are identified and mitigated as far as reasonably practicable. Lightning event risks to internal systems are associated with the breakdown of insulated cables causing sparking between cores and equipment loss/failure causing fire, explosion, and electric shock. Transient switching overvoltages caused by the power grid or internally via motors, lighting, and other M&E equipment can be just as damaging to sensitive equipment, more often the damage is incremental, causing interruption/ premature failure of devices or corruption errors within programmable devices. With proper design and coordination, protecting against these causes will minimise risk and ensure compliance is met. For all COMAH and DESEAR regulated sites, coordinated SPM is mandated.

Test and inspection of surge protection measures

Test and inspection is a regulated requirement of BS7671 18th edition and a requirement under the BSEN 62305 lightning protection standard. Periodic T&I is to meet the building owners/occupiers’ responsibility under the Electricity at Work Act 1989.

See BS7671 18th Edition IET wiring regulation 534.4.1.1 Test & Inspection regulations 642, 643.10, 651.2 (v, vi), note 1, 651.4, 652.1 & annex 6 page 468 (page 516 in amd. 2) Also BSEN 62305-3 Clause 7, E.7. & and BSEN 62305-4, 9.3

Firstly, we must be mindful that surge protection is a necessary and mandated requirement under BS7671 and BSEN 62305. These devices are installed to prevent harm and loss of life, prevent loss of safety systems as defined in part 2 of BS7671, and protect against financial loss and loss of data.


Q. Is checking SPDs a requirement of BSEN 62305?

A. this is required under BSEN 62305-3 clause E.7 and BSEN 62305-4 clause 9.3

Q. Is a ‘visual inspection only’ required under the standards?

A. No, both visual and electrical testing is required as per the BSEN 62305 clauses above.

Q. I have been told that electrical testing of SPDs is not required under my LPS inspections; is this correct?

A. No, the SPDs under BSEN 62305 are an integral part of the overall LPS system protection and must be inspected/ tested/measured as required under BSEN 62305-3 E.7. SPDs within the SPM design under BSEN 62305-4 9.3 must be electrically tested to verify both function and continuity with the earth bonding system. The measured results must be logged and any defects rectified without delay. The full SPM must be visually inspected including OCPDs and wiring etc. under both clauses

Q. Can these inspections/ tests be carried out as separate actions?

A. Yes, it would not be unreasonable given the differing technical skills and access requirements that the external LPS Faraday cage network system be inspected and tested separately following the majority of BSEN 62305-3 E.7. The internal SPM inspection measurement and testing requirements shall be carried out following BSEN 62305-3 clause E.7 and BSEN 62305-4 clause 9.3

Q. Is periodic checking of the SPDs part of the testing and inspection requirements within BS7671? If so, how often and what is required?

A. Yes, this is a requirement. The applicable regulations are 651.2 (v, vi), note 1, and 651.4. This periodic requirement follows on from the need to inspect the SPDs under regulation 642.3 and functionally test the SPDs under regulation 643.10. The frequency of periodic inspections and testing is determined by regulation 652.1 recorded as required to regulation 653 in an EICR (electrical inspection condition report, see appendix 6) BS7671 18th edition, appendix 6 page 468 (page 516 amd. 2) states that SPDs are to be confirmed where these have been specified under regulation 534.4.1.1 This regulation states why and where each SPD is required and thus should be checked to see if these are present and have been correctly installed. Regulation 651.4, periodic inspection & testing states: “Details of any damage, deterioration, defects or dangerous conditions shall be recorded in a report “.

As regulation 651.4 is specifically asking for details of any damage, deterioration or defects to be recorded, then along with visual inspection of the device/ wiring/connections and OCPDs, per 642.3, the measured functional test of the device shall also be periodically undertaken and recorded as per 643.10. It is not a simple visual checking of the SPD indicator flag as these do not indicate deterioration which may render the device ineffective/ unserviceable or in a dangerous condition. The consequence of inadequate overvoltage protection is clearly stated in BS7671 regulation 443.4 including but not limited to the risk of serious injury and loss of life. It is therefore vital that SPDs are periodically checked and functionally tested to ensure the intended protection levels remain within the manufacturer’s specification when first installed and not deteriorated beyond the manufacturer’s specified operational performance range.

Periodic surge protection inspection/testing to BS7671 should be harmonised with the periodic inspection/testing for lightning protection & surge protection measures of BSEN62305-3 clause E.7 & BSEN 62305-4 clause 9.3. The maximum intervals are as BSEN 62305-3 Table E.2 inc. Notes a.& b.

Q. Does testing of the SPD cause reduction of the expected life span

A. No, as long as the test equipment being used for the test has been specifically designed for testing SPD active components capable of producing a constant current to 1mA max. and sequential ramp rate voltage of up to 1.5KVDC. The test does not reduce the SPD component expected life span as the ramp voltage applied is cut off as soon as the component under test changes state (voltage lets 1mA to pass through MOV / ABDs, Ionises the GDT spark gap to allow a spark across its terminals) Generic multi-test equipment not specifically made to test SPD components to the required specification standard IEC 61643-311 (GDT, Gas Discharge Tube / Spark Gap), IEC 61643-321 (ABDs, Avalanche Breakdown Diodes) & IEC 61643-331 (MOV, Metal Oxide Varistors) may damage the components under test or give a false result.

Q. What action is required if a defect is raised under BS7671 or BSEN 62305?

A. Dependant on the results from the BS7671 inspection and testing of SPDs, a C2 potentially dangerous defects report shall be recorded and any defect found must be rectified without delay. If not an immediately potentially dangerous defect; a C3 improvement recommendation can be made, i.e., a need for additional SPDs on any unprotected lines since the last inspection report Ref 534.4.1.1. These are the same actionable requirements if the inspection and test were carried out under BSEN 62305, however, unlike BS7671, the BSEN 62305 standard requires that SPDs are inspected/tested where installed on all conductive lines, i.e., telecom, signal and control, RF, PV DC strings etc. not only LV main and sub-main distribution lines. For BSEN62305-3 compliance certification, all conductive lines leaving/entering the structure which has a lightning conductor system installed must have an SPD installed to each conductive line. These Type1 equipotential bonding SPDs shall be installed as close as practically possible to the entry position inside the structure. For BS7671 534.4.1.1 and BSEN 62305-4 coordinated surge protection measures must be in place to confirm compliance.

Why is SPD inspection testing and measurement logging important?

Performance degradation – Functional operational status testing under BSEN 62305

Installed SPDs have been measured for degradation rates and failure rates over time. SPDs should be servicable from 2Yrs to up to 20Yrs although we are now seeing SPD lifespans being further reduced due to many more switching transient events within buildings. These events can be relatively small but repetitive in nature, any lifespan reduction is directly proportionate to the number and magnitude of events, for example, switched banks of lighting, elevators, air handling and conditioning, industrial plant or machinery motor use. Each building will have one or more of these and other switched load circuits that may produce momentary transients. The reduction in lifespan is not something that is normally flagged by a device’s thermal trigger. These triggered indication flags are to show the device has absorbed a single event that has caused a rise in temperature beyond a solder cap set temperature melting point releasing a spring mechanism changing the indicator flag and if present closing a set of remote monitoring contact output terminals.

For SPDs using GDT spark gap protection, Indicator flags if present use the same thermal melt device to operate. Degradation of GDTs is measured across the electrodes by way of introducing a ramp voltage to the point of trigger (spark jumps across the gap) Again this test is to establish if the GDT remains within the manufacturer’s quality performance range. Unlike the MOV absorption degradation test, (measured voltage at which a MOV allows a 1mA flow) GDT performance is degraded due to pitting, distortion, and wear of the electrodes caused by each sparking event. The point of trigger voltage is logged and if found to be outside the manufacturer’s serviceable range, the device must be replaced.

Testing SPD components periodically is the only way to determine whether the device remains serviceable within the manufacturer’s quality performance range see BSEN 62305-4 9.3.

Inspection and testing of SPDs can be done during planned annual periodic maintenance in accordance with BSEN 62305-3 E.7, BSEN 62305-4 9.3. Also see BS7671 regulations 642.3, 643.10 & 651.4. BS7671 periodic testing intervals is dependent on the need, and in line with BSEN62305 due to external influences such as Lightning as well as transmission line overvoltages.

BSEN 62305 E.7.2.3 Visual inspections

-there has been no indication of damage to the LPS, to SPDs, or any failures of fuses that protect SPDs,

– correct equipotential bonding has been established for any new services or additions which have been made to the interior of the structure since the last inspection, and continuity tests have been performed for these new additions,

bonding conductors and connections inside the structure are present and intact (functionally operational),

– separation distances are maintained,

– bonding conductors, joints, shielding devices, cable routing and SPDs have been checked and tested.

E.7.2.4 Testing

“SPDs without a visual indicator need to be tested, preferably using the guidelines or equipment provided by the manufacturer”

This statement must not be misinterpreted. SPDs with visual indicators are not exempt from testing! Tests undertaken as prescribed within clauses E.7.2.3 & E.7.2.4 are to check both electrical earth continuity and operational function remains within manufacturer tolerance, not a total failure of the device which is the purpose of thermal activated mechanical indicator flags if present – also see BSEN 62305-4-9.3

BSEN 62305-3 E.7.2.4 NOTE 1 High-frequency or impulse measurements are possible and useful to determine the high frequency or impulse behaviour of the earth-termination system. These measurements may be performed at the installation stage as well as periodically for the maintenance of the earthing system to check the adequacy between the designed earthing system and the need.

It must be remembered that SPDs are an integral part of the earth bonding system as per BSEN 62305-3 6.2.4, 6.2.5, E.6.2.2. The SPM earth bond is only made when the SPD activates, therefore the SPDs must be functionally tested to verify the bond will be made as intended. This is done by using appropriate test equipment as per Note 1 above. “to check adequacy between the designed earthing system and the need”

Providing an earth loop impedance test or continuity test for the earth cable connection does not provide any evidence that the SPD will perform its design earth bonding function. This can only be done by use of a specifically designed SPD tester.  

BSEN 62305-4

9.3 Inspection of SPM (Surge Protection Measures)

9.3.1 General

The inspection comprises checking the technical documentation, visual inspections and test measurements. The object of the inspection is to verify that – the SPM complies with the design,

– the SPM is capable of performing its design function, (Functional test measurements of SPD components as required above is the only way to confirm each SPD remains within manufacturer tolerances to perform its design function as part of the SPM)

– any new additional protection measure is integrated correctly into the SPM.

 Inspections shall be made

– during the installation of the SPM,

– after the installation of the SPM,

– periodically,

– after any alteration of components relevant to the SPM,

– possibly after a lightning flash to the structure (e.g., where indicated by a lightning flash counter, or where an eyewitness account of a flash to the structure is provided, or where there is visual evidence of lightning-related damage to the structure). Measurements

A measurement of electrical continuity should be performed on those parts of an earthing and bonding system that are not visible for inspection. (Electrical testing to trigger the SPD and record the actual voltage point necessary to make the Earth continuity bond is the only way to ensure this Earth path works when required) (SPDs are equipotential bonding devices)!

NOTE If an SPD does not have a visual indicator (flag), measurements shall be performed in accordance with the manufacturer’s instructions to confirm its operating status, when so required.

This statement must not be misinterpreted. It does not conclude that SPDs with visual indicators are exempt from testing! Thermal activated mechanical flags do not indicate functional degradation only total failure. Periodic testing to confirm the SPM performs to its design function is required in this standard and the UK wiring regulations BS7671 18th edition. 

9.3.3 Inspection documentation

An inspection guide should be prepared to facilitate the process. The guide should contain sufficient information to assist the inspector with his task, so that all aspects of the installation and its components, tests methods and test data which is recorded, can be documented. The inspector shall prepare a report, which shall be attached to the technical documentation and the previous inspection reports. The inspection report shall contain information covering

– the general status of the SPM, (Do the SPDs in the system measured test data results recorded remain within the manufacturer performance range?  Is the surge protection measures complete and in a serviceable condition)?

– any deviation(s) from the technical documentation,

– the result of any measurements performed.

9.4 Maintenance

After inspection, all defects noted shall be corrected without delay. If necessary, the technical documentation shall be updated.

These annual tests can be carried out by a person competent in the use of the Raycap ProSCT tester. The tester will automatically detect the protective component within each SPD and automatically select the correct test voltage/current to be applied. Each SPD manufacturer will have a quality performance range for their product under test. If this is unavailable a known comparable manufacturer range can be used

Defective SPD products, ones that have test results out with their manufacturer’s quality performance range shall be corrected without delay as per BSEN 62305-4 9.4 above.


Regular Periodic Testing and Inspection of SPDs is of vital importance in order to maintain effective life safety measures against shock, fire, or explosion and to prevent damage to electrical systems, protect critical operational services from interruption/loss under the Lightning protection standard BSEN 62305 and IET wiring regulation BS7671 18th edition.

The clauses listed within these standards are freely available to read to independently verify the statements made in this publication.

LSS Ltd is the official UK partner/ distributor of Raycap® and stock the Raycap ProSCT backlit touch screen tester along with a full range of enhanced Raycap SPDs that can be used to replace any older/ defective device no matter what manufacturer SPD has been previously installed

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