Earthing Conductor Sizing Calculator
Size an earthing/protective conductor from prospective fault current and disconnection time, using the IEC 60364-5-54 adiabatic equation (S = I x sqrt(t) / k). Pick a material/insulation preset instead of having to already know the k constant, and get the result rounded to the nearest standard IEC 60228 conductor size. Runs entirely in your browser.
Input
The maximum fault current the protective device would see — from a fault-loop/short-circuit study.
How long the protective device (fuse, breaker) takes to clear the fault.
Sets the k constant from a common IEC 60364-5-54 Table 54.2 figure. Pick Custom to enter your own.
Enforce a code-mandated floor (e.g. 6mm² for a bare copper earthing conductor), if one applies.
Output
| Item | Value |
|---|---|
| No data yet | |
Guides
Turn a prospective fault current and a protective device's disconnection time into a minimum earthing/protective conductor size, using the adiabatic short-circuit equation from IEC 60364-5-54 (mirrored by BS 7671 regulation 543.1.3 and most national wiring codes) — rounded up to the nearest standard IEC 60228 conductor size.
Most quick versions of this calculator make you already know the material constant k before you can use them at all. This one picks it for you from a plain-language material/insulation choice — copper vs. aluminum vs. steel, PVC vs. XLPE vs. bare — with a Custom option when your code's own table gives a different figure (bunched conductors and cable cores are limited by the touching insulation and use a lower k than a free-standing conductor).
How to use it
- Enter the prospective fault current in kA — the maximum current the protective device would see, from a fault-loop or short-circuit study.
- Enter the disconnection time in seconds — how long the fuse or breaker takes to clear the fault.
- Pick the conductor's material and insulation. This sets the k constant from a standard IEC 60364-5-54 Table 54.2 figure for a conductor not incorporated in a cable and not bunched with other cables. Select Custom to type your own k when that assumption doesn't hold.
- Set a minimum standard size, if your code mandates a floor (a bare copper earthing conductor is commonly required to be at least 6mm², for example) — otherwise leave it at "No minimum."
- Read the calculated theoretical area and the recommended standard size, rounded up from the full IEC 60228 preferred series (1.5mm² through 630mm²).
The formula
S = I × √t / k
Where I is the fault current in amps, t is the disconnection time in seconds, and k is a material/insulation constant representing how much energy per unit cross-section the conductor can absorb before exceeding its temperature limit. The result is rounded up to the next standard conductor size — a conductor smaller than the calculated area would overheat before the protective device clears the fault.
Where do the k values come from?
They're the commonly published figures from IEC 60364-5-54 Table 54.2 for a bare or single-insulated protective conductor that stands on its own — not run as a cable core and not bunched against other insulated conductors. A conductor in either of those situations is thermally limited by the touching insulation (usually lower than the conductor's own rating), so it needs a lower k from your code's own table — that's what the Custom option is for.
Does this cover everything needed to size an earthing system?
No — deliberately not. This is the adiabatic thermal check only. A complete earthing design also needs the electrode's resistance-to-earth (see the Earthing Grid Resistance Calculator for a buried grid), the earth-fault loop impedance, and a touch-voltage assessment — none of which this tool attempts, since they need site-specific soil and layout data this calculator has no way to know.
Is this a substitute for a qualified electrical engineer?
No. This applies the standard adiabatic equation from a fault current and clearing time you supply. It doesn't know your installation's actual fault levels, protective device curves, or local code amendments. Get a qualified electrical engineer to review before relying on this for a real installation.
Related tools
Sizing the breaker or fuse that sets your clearing time? The Circuit Breaker Sizing Helper recommends an ampere rating from load current. For the earth electrode side of the system, see the Earthing Grid Resistance Calculator.
Use it from code
From 3 credits per callREST API
curl -X POST https://api.iotools.cloud/v1/tool/earthing-conductor-sizing-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"faultCurrent": "10",
"clearingTime": "0.5",
"materialPreset": "copper-pvc",
"minSize": "0"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `earthing-conductor-sizing-calculator` tool (Earthing Conductor Sizing Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.