IEC 62305 in Greece
Greece runs the same IEC 62305-2 method as everywhere else, with one recorded departure that is blanket rather than selective: the thunderstorm warning system factor P_TWS is 1 for all cases.
Greece applies the IEC 62305-2 risk method unchanged, with one recorded departure that reaches further than most: the thunderstorm warning system factor PTWS is 1 for all cases.
The standard says so in its own text. IEC 62305-2:2024 carries a list of differing practices in its foreword, at printed p.9, and the Greek entry records that the value of PTWS = 1 for all cases is assumed. Three words in that sentence do the work: all cases. The Greek rule is blanket, where the German rule on the same factor is written per risk component.
This page sets out what PTWS is, which six probabilities carry it and which three do not, what holding it at 1 does to a result and in which direction, and how the blanket form differs from Germany's. Everything cites the clause, equation or table it comes from, because a parameter rule you cannot trace is a parameter rule you cannot defend in a review.
Which publication governs in Greece
Greece reaches IEC 62305 the way its neighbours do. CENELEC adopts the international standard as EN IEC 62305, and the Greek national body, ELOT, publishes that text under a national reference. The clauses, the risk components and the equations come across unchanged, which is why a Greek specification and an international one describe the same method.
The naming is worth getting right on a document. The current series is IEC 62305 and its adoptions carry the IEC number in their designation, as in EN IEC 62305. A bare EN 62305 refers to the superseded 2011 series and is not the standard a current assessment is built to. If a specification you have been handed names that number, resolve which edition is actually intended before you calculate, because the edition decides the method.
None of this changes the method. The reference number tells you which national publication governs; the differing practices list tells you what that country changes. For Greece the answer to the first is the European adoption, and to the second it is PTWS. For the wider picture of how adoption works, see IEC 62305 around the world.
What PTWS is and where it enters
A probability term from Annex B, multiplying into six of the nine damage probabilities. Knowing which six is what tells you where the Greek rule bites and where it does nothing.
The factor
PTWS is the thunderstorm warning system factor: the probability that the system fails to give warning in time for the mitigation it enables. Clause B.2 NOTE 1 assumes PTWS = 1 where no warning system is provided or no reduction factor FTWR is declared. Selecting a value below 1 is what claims credit for the system.
Where it appears
PTWS is a multiplicative term in PAT, equation (B.2), PAD, equation (B.3), PU, equation (B.10), PV, equation (B.11), PW, equation (B.12) and PZ, equation (B.13). Those six probabilities drive the risk components RAT, RAD, RU, RV, RW and RZ.
Where it does not
Equations (B.4) PB, (B.5) PC and (B.6) PM carry no PTWS term. So RB, RC and RM are arithmetically untouched by the Greek rule, however the entry is worded. A blanket instruction cannot reach a term that is not in the equation.
PTWS is a probability of failure, not of success. That sign convention is the one thing to hold on to when reading the rule, because it decides the direction of the effect: a larger PTWS means a less effective warning system, and 1 means no credit at all.
What holding PTWS at 1 does to a result
Because PTWS multiplies into the six probabilities above, fixing it at 1 leaves each of them at its unreduced value. The six components RAT, RAD, RU, RV, RW and RZ are therefore higher than the same building would produce under a plain IEC baseline calculation that declared a warning system, and the total risk R rises with them.
The direction is one way. Setting a failure probability to its maximum can only raise the affected components, never lower them. So the Greek rule never rescues a structure that would otherwise fail; it can only push one that was passing over the line. That is the opposite of the Italian rule, which is more permissive than the baseline, and it is worth stating plainly because the two are often filed together as national departures without noticing they move in opposite directions.
The size of the difference is the size of the credit that was being claimed. A structure with no thunderstorm warning system already sits at PTWS = 1 under clause B.2 NOTE 1, so the Greek rule changes nothing for it. The rule bites exactly where a warning system has been declared and a value below 1 selected, and it scales with how much reduction that selection was taking out of the calculation.
The decision that can flip is whether protection is needed at all. The verdict in IEC 62305-2 is a comparison of the computed risk against the tolerable value. A building carried just under that line by a declared warning system sits above it once the credit is removed. So the departure is not a rounding detail. It can be the difference between a report that says no protection is required and one that specifies a lightning protection system.
Why the Greek rule reaches further than the German one
Germany and Greece both force PTWS to 1. The entries are worded differently, and that wording changes which components are affected.
Greece, blanket
The entry records the value for all cases, so it reaches every probability carrying the term: PAT, PAD, PU, PV, PW and PZ. That includes the person injury group, the touch and step voltage components RAT and RAD and the injury component RU.
Germany, per component
The German entry names RB, RC, RM, RV, RW and RZ, and does not name RAT, RAD or RU. Since PB, PC and PM carry no PTWS term, the German rule effectively reaches three components where the Greek rule reaches six.
The difference matters in both directions. Applying Greece's blanket rule to a German assessment would inflate RAT, RAD and RU, which the German entry deliberately leaves alone; applying Germany's component list to a Greek one would understate those same three. Overstating risk is as wrong as understating it, because both put a figure in a report that the governing rule did not produce. Germany's own departure on the fire provisions factor is covered in IEC 62305 in Germany.
RT is representative, not fixed by the standard
It is common to see the tolerable risk quoted as though IEC 62305-2 fixes it. It does not. Clause 7.3 NOTE 1 gives RT = 1×10-5 per year as a representative value of tolerable risk and adds that another value may be set once the case has been investigated in detail. Printed p.12 then lets national or local regulations fix RT, the tolerable frequency of damage FT, and the Annex A, B, C and E calculation rules and parameter values.
For Greece the standard records no national RT, so an assessment uses the representative value unless a project specification, a regulator or the authority having jurisdiction names another. That is a judgement to make and record at the start of a project, with whoever is entitled to make it, rather than a number to assume. It is also why a tool should resolve the tolerable value from the jurisdiction rather than carry it as a constant in the code.
Related reading
For how national adoption works generally, and which designation applies in other markets, see IEC 62305 around the world. For the method the Greek rule modifies, read the IEC 62305-2 risk assessment, and for the arithmetic itself see how IEC 62305 risk is calculated.
Three other national departures are set out in their own pages: IEC 62305 in Germany, where the fire provisions factor rp is 1 for all cases, IEC 62305 in Italy, where RL1 and RL2 are compared with the tolerable risk separately, and Annex D and Annex E in national practice, which covers the Netherlands and South Africa.
Select the jurisdiction before you compute
In Lumex the jurisdiction is an input, not an afterthought. Selecting Greece forces PTWS to 1 across every component that carries the term, before the calculation runs, so the figures in the report are the Greek figures rather than baseline figures with a note attached. It is applied server side, which is the part that matters on a compliance job: a warning system declared in the inputs cannot pull a Greek assessment below what the regulator permits, because the credit is removed after the input is read and not left to the engineer to remember. The report then prints the departure with its citation, so a reviewer can tell a regulator's rule from a modelling choice. See the Lumex platform.
Questions answered
Does Greece use IEC 62305?
What is P_TWS in IEC 62305-2?
Which parts of the calculation does P_TWS enter?
What does P_TWS = 1 change in a Greek assessment?
How is the Greek rule different from the German one?
Is a thunderstorm warning system pointless in Greece?
Is the tolerable risk different in Greece?
Lumex computes the IEC 62305-2 method and shows the working. It does not certify a structure. You may not issue or submit a Lumex output until a competent person, qualified where the structure is located, has reviewed the inputs and the result and signed it.
The tolerable risk in IEC 62305-2 is not a fixed constant. Clause 7.3 NOTE 1 gives RT = 1×10-5 per year as a representative value of tolerable risk and adds that another value may be set once the case has been investigated in detail. Printed p.12 then lets national or local regulations fix RT, the tolerable frequency of damage FT, and the Annex A, B, C and E calculation rules and parameter values. Every Lumex assessment states the jurisdiction it was computed under and the values that applied.