Calculate protective earth conductor (building and boat)
Computes both permissible IEC paths — adiabatic S = √(I²·t)/k and the simplified assignment from the phase conductor — and recommends the next commercial size. The marine mode sets it apart from every building calculator: on boats the hull is a live structural conductor, and faulty grounding on shore power eats anodes, shafts and hulls.
The formulas behind the calculator
Every number above can be recomputed: the full calculation path, all assumptions and the data source with retrieval date — plus cross-validation against independent references. Disclosed, not claimed.
Safety-relevant calculation. This is an estimate based on the stated assumptions. The final design must be checked by a qualified electrician against the rules that apply where you are.
The technical review of this safety-relevant calculator is still outstanding.
| Step | Formula | Value | Provenance |
|---|---|---|---|
| Adiabatic proof | S = sqrt(I^2 * t) / k | 4.4228 mm^2 | assumed |
| Simplified assignment | S<=16: S | 16<S<=35: 16 | S>35: S/2 | 16 mm^2 | exact |
- Formula
16<S≤35: 16- Valid for
- Building mode: both permitted IEC 60364-5-54 routes side by side — simplified table (reference: 16 mm² at 16 mm² line) and adiabatic formula S = √(I²t)/k (reference: 4.42 mm² at 1,000 A / 0.4 s / k=143); k is USER INPUT with a source reference (standard tables are not reprinted), recommendation conservatively at a standard size. Boat mode: galvanic assessment from hull material, shore power and isolator against 33 CFR 183 (public domain) with a verified ISO edition — an aluminium hull on shore power without an isolator is critical.
- Not covered
- Earthing concepts (TN/TT/IT), earth electrodes and bonding, lightning protection, the IEC k tables themselves (user input), stray-current corrosion from DC faults, flag-state special rules.
Frequently asked questions
Which of the two calculation paths applies?
Both are permissible under IEC 60364-5-54, and the stricter one wins: the simplified assignment (equal up to 16 mm², fixed 16 for 16–35 mm², half the phase conductor above) is the quick table path; the adiabatic proof S = √(I²·t)/k computes the actual thermal stress under fault. With short disconnect times the simplification usually yields larger sizes — the calculator shows both and rounds the governing one up to the next commercial size.
Where do I get the material factor k?
From tables 54.2–54.6 of IEC/DIN VDE 0100-540 — depending on conductor material, insulation and installation (in a cable or separate). Those standard tables are copyrighted and deliberately not reproduced here (annex B11 of the project specification): k is therefore user input with visible assumption marking. The default 143 applies to PVC-insulated copper not run in a cable — for other cases consult the standard or a reference book.
Why a dedicated mode for vehicles and boats?
Because building logic simply does not apply there: body and hull are live structural parts, there is no earth electrode in soil, and on boats salt water joins as an electrolyte. The questions shift from “which cross-section?” to “how are protective earth, negative and hull bonded — and what happens on shore power?”. Exactly these questions the marine mode asks, assessing the galvanic risk.
What makes shore power so dangerous for boats?
The protective conductor: for safety it bonds your boat to the dock — and thus galvanically to every neighbouring boat on the same feed. Dissimilar metals under water (your prop, the neighbour’s anodes) form a cell across that path, and the least noble metal sacrifices itself — creeping, for months, until anodes are gone and shafts or hulls are attacked. A galvanic isolator (diode block) or an isolation transformer breaks the DC path without sacrificing shock protection.
Which standards govern on board — and what does the calculator use?
Governing is ISO 13297:2020 with Amendment 1:2022 — since 2020 it unifies AC and DC installations (the old DC standard ISO 10133 merged into it); plus ABYC E-11 in the USA and, for gasoline-engine boats, US federal law 33 CFR 183. The calculator uses what is freely and legally usable: the public-domain CFR facts (fuse within 72 inches of the battery terminal, minimum sizes AWG 16/18) plus the verified ISO edition as a reference. Concrete ISO sizing remains with the standard and a marine-qualified electrician.
Is this calculator sufficient for commissioning my installation?
No — and it says so: it delivers both standard calculation paths, the commercial-size recommendation and, in marine mode, the risk assessment, but no loop-impedance measurement, no selectivity check and no ISO-compliant final inspection. Protective conductors are shock protection: final sizing and testing belong to a qualified electrician — on a boat, one with marine qualification.
Why two calculation routes for the protective conductor?
Because IEC 60364-5-54 permits both: the simplified table (equal cross-section up to 16 mm² line conductor, stepped above) and the adiabatic formula S = √(I²t)/k. In the reference case the table demands 16 mm², the formula proves 4.42 mm² — the calculation route thus permits the smaller conductor, but costs the proof with fault current and disconnection time. The page shows both routes side by side and recommends conservatively.
Where does the material factor k come from — and why is it an input?
From the IEC 60364-5-54 tables, which state different k values by conductor material, insulation and start/end temperature — 143 applies to insulated copper (PVC) run separately. The tables are protected standard text and are not reprinted here: k is user input with a source reference, the same discipline as the ampacity calculator. Every output says so.
What distinguishes the vehicle/boat mode from the building mode?
The problem itself: on a boat it is not about disconnection conditions but galvanics. Shore power connects your hull via the protective conductor to every neighbouring boat — without an isolator an aluminium hull becomes the marina's sacrificial anode. The mode checks hull material, shore connection and galvanic isolator against the public-domain US rule (33 CFR 183) and the verified ISO edition.
How serious is the galvanic warning for an aluminium hull?
The calculator's most serious: aluminium is less noble than almost anything hanging in marina water — bronze propellers, stainless shafts, copper in the protective conductor. With shore power and no isolator the current flows permanently, and the loss is structural, not cosmetic. The calculator rates this critical and names the isolator (or isolation transformer) as the precondition.
Does the calculator replace earthing design?
No — it sizes the protective conductor along the permitted routes and checks the boat configuration against known fault patterns. Earthing concepts (TN/TT/IT, earth electrodes, bonding) are professional planning; on boats the flag state's standards add to it. Both modes state their limits explicitly.