How the SPM engine is validated.
An SPD specification decides what a contractor buys and what survives a strike. So the numbers behind it cannot be a black box. Here is exactly how the Voltbench engine is checked — including the places where a published source disagrees with it, and what was done about that.
Four layers, not one claim
Each layer catches a class of error the one before it cannot.
Every constant cites its clause
Tables C.1 to C.5, Table D.1's preferred ratings, Table B.8's signal-line currents and the equations of Annex C are transcribed cell by cell from IEC 62305-4 Ed. 3.0:2024 and its companion parts, with the clause printed beside the value on the report.
The standard against itself, and its siblings
Part 4 states several quantities twice, and Parts 1 and 2 state them again. Table C.3 is reconciled against the D.3.2 derivation, Table B.8 against Part 1's Table E.2 cell for cell, Table C.1 against Table A.2. A transcription slip cannot survive four books printing the same number.
Eight independent published sources
Layers 1 and 2 cannot catch a misreading shared with the book. So the figures are checked against parties who arrived at them by their own route — manufacturer design guides, a different standards lineage, and the ITU recommendation the IEC itself cites. Listed below.
Through the real product, by browser
Four complete designs are driven through the actual wizard by browser automation and the rendered page is checked, not the engine's return value. That layer found a defect the engine tests could not: a correct number that lost its label on the way to the screen.
The independent sources it reconciles against
The two liability-critical outputs — the required discharge current and the voltage protection level — are each reproduced from more than one independent published source.
power lines
signal lines
level & leads
Sources, for reference: DEHN, Lightning Protection Guide, 3rd updated ed.; ABB, Surge and lightning protection solutions; HD 60364-5-534:2008, clause 534; Schneider Electric, Electrical Installation Guide, ch. J; Legrand, Modular Surge Protection Devices; ITU-T Recommendation K.67 (12/2015); nVent ERICO, Lightning Protection Handbook. Voltbench reproduces the method and prints its own figures; it does not republish these documents or the standard's tables.
One published source disagrees, and it is on the record
A manufacturer's handbook reads IEC 62305-1's Annex E as a total for the service, to be divided by the number of conductors — which would put a three-phase entrance four times lower than Voltbench specifies. The standard's own note says the values refer to each line conductor, a footnote elsewhere in the same table only makes sense on that reading, and the ITU recommendation the table cites derives it per conductor. Voltbench follows the standard, states which basis it used on every report, and keeps the disagreement written down rather than quietly winning it.
Where the checking is thinner, the report says so
Not every figure has an outside witness. Table C.5's values and four of Table B.8's five columns rest on the standard and its siblings alone; no published source states an equivalent table. Where a Voltbench figure sits below a threshold another standard would apply — as Table C.5 does against IEC 60364-5-534's fallback — the report discloses both, rather than presenting the more convenient one.
See the trace for yourself
The sample report shows the full working on one fixed design — every required current with its clause, the calculation trace, and the assumptions and exclusions in full. Read it, then run your own.
Voltbench is a calculation aid for qualified electrical engineers. Its outputs support, and do not replace, the professional judgement of a licensed engineer of record, who remains responsible for the design and its verification against the governing standard.