PQRS Simplified Lightning Risk Assessment Calculator - IEC62305-Ed3:2024
Welcome to the PQRS Simplified Lightning Risk Assessment Calculator. This tool provides a quick, practical first assessment for simple sites or users who are new to lightning risk assessments. To get started, enter the project details and work through the six guided steps covering the site, structure, and any existing lightning protection measures. The calculator will then estimate whether the risk remains above acceptable levels in line with IEC 62305-2, and indicate whether additional protection may be required.
This is a quick assessment. The detailed calculator will be available soon.
This is a quick assessment. The detailed calculator will be available soon. Leave your name, email, and a mobile number with the country code. We will email you when it is ready, and about other PQRS tools. Tick WhatsApp if we may message that number.
Who is this for, and where is the building?
This does not change the sums. It sits on the report so anyone can see which site was assessed. You can fill it now or just before you print. Your company details will later come from your login. Type them here for now.
The job
Who is doing the assessment
Next: open step 1 and set the flash density for this site.
1 Lightning strike frequency in the area
Look up the flash density for this site. Use a lightning map or a location system. We do not pick a town for you. Regional lists can come later. The 14 in the box is only a starter — replace it. We usually multiply by 2 to get strike-point density, unless your location system already gives that number.
Next: open step 2 and describe the building and the lines into it.
2 How many dangerous events do we expect?
You do not type those four counts yourself. Size, height, and where the building sits tell us hits on and near the building. Power and telecom lines tell us hits on and near a connected line. Fill this step, then calculate the counts. You do not need steps 4 to 6 yet.
Power line into the building. If you do not know the length to the first node (a transformer, a cabinet, or the next structure), IEC 62305-2 uses 1 000 m. We use that here. Log in to type a known length. If you know the HV and LV sections, or if PV DC comes into the building, use the long form.
Power line into the building. If you know the length to the first transformer, cabinet, or next structure, type it. If you do not know, leave 1 000 m — that is what IEC 62305-2 uses when the length is unknown. Maximum 2 000 m. HV and LV as separate sections, or PV DC into the building, still belong on the long form.
Optional second line (telecom or data). Same rule: 1 000 m if the length is unknown. Log in to type a known length. For Cat6 or RS485 comms cables (solar-related comms, not the DC strings), use the long form if you also need screen or isolation picks.
Optional second line (telecom or data). Type the real length if you know it. Leave 1 000 m if you do not. Maximum 2 000 m.
These are expected hits per year from steps 1 and 2. Hits near the building or near a line also use the equipment withstand from step 4 — 2.5 kV until you set it there.
Next: step 3 is a short map of where those hits come from. Then step 4 is the protection already in place.
3 Where did the lightning come from?
There is nothing to type here. Lightning can reach the building in four ways. The calculator uses all four automatically from steps 1 and 2.
Next: open step 4 and say what protection is already there.
4 Risks against equipment based on site layout
If lightning does reach the building, how likely is damage? That depends on the structure, any LPS already fitted, bonding at the incoming lines, surge protection, and how the internal wiring is run. For withstand, pick a value from the standard list. Inverter sheets usually say a category, not kilovolts: category I is 1.5 kV, II is 2.5 kV, III is 4 kV, IV is 6 kV on a 230/400 V board. Use the lowest on that line.
First line: if a hit of that kind happens, how often would this follow. Second line: that chance times the hit counts from step 2, as a rough “how often on this site.” This is still not the final yearly risk. Step 5 still changes how bad a fire would be.
Next: open step 5 and say who could be hurt and how bad a fire would be.
5 Risks against people and fire
Two kinds of loss sit in this check: harm to people, and fire or physical damage. How often people are there, and how easily a fire could start, change the result.
This box is only for people out in the open on the building, where a flash could strike them. Touching galvanised walls from the ground is the shock path in step 4.
If lightning hits, how easily can a fire start, given what the building is made of and what is inside it. A thatch roof, a timber barn, a paper store, or a lot of loose packing is High. An ordinary brick house with normal furniture is Low or Ordinary. A concrete store with almost nothing that can burn can be None.
This is your call for this site, not a fixed building type. If a fire would take the owner’s only home and assets, pick High. If it is one barn among many on a farm, the loss may be Low.
Next: open step 6 to add the two paths and see if the total is still okay.
6 Sum the risks and see if it is okay
The ‘People-path’ plus ‘fire / damage-path’ gives the overall risk. The usual limit is about 1 in 100,000 per year. We also check how often internal systems would be damaged and if a check fails, the note below will show which factors caused the failure.
Users can go back into the calculator and change the indicated factors that caused the Risk to be too high, run the assessment again. How the LPS is built is specified in IEC 62305 Part 3 and how to fit surge protection is included in IEC 62305 Part 4.
This value is for the amount of time the electrical equipment is live and able to be damaged throughout the year.
Leave it at “all year” unless it is seasonal or a standby board that is off for extended periods of the time.
This is how often a damaging hit to the electrical equipment is still okay. Once a year is ordinary plant. Three and five years sit between that and the usual ten-year pick. Once every 20 years is tighter. Damage cannot be tolerated means any damaging event fails this check and might be applicable to explosive environments.
A PDF report will be available when you have a report allowance.
People path, fire path, then the total. The right-hand column is the symbol used in the standard.
| What this is | In the standard | Number |
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