CALCULATORS / WIRES, CABLES AND HARNESSES

Fuse continuous current derating calculator

Operating current versus supplied derated fuse current; no trip-curve coordination solve.

wires-fuse-coordination.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	continuousBudgetA	marginA
	7.5	2.5
	7.5	3.5

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

continuous-current screen5.00 A✓ passes

BASELINE INPUTS

operatingCurrent5 AfuseRating10 Aderating0.75

CALCULATED

continuousBudget7.5 A

margin2.5 A

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Fuse and load-curve comparison
# Scope: Operating current versus supplied derated fuse current; no trip-curve coordination solve.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

operatingCurrent = 5 A
fuseRating = 10 A
derating = 0.75

continuousBudget := fuseRating*derating [A]
margin := continuousBudget-operatingCurrent [A]

check continuous-current screen: operatingCurrent <= continuousBudget

scenario alternative: operatingCurrent = 4 A

Calculated from your source · not saved

Baseline · Baseline

continuous-current screen5.00 A ✓ passes

alternative · alternative

continuous-current screen4.00 A ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

continuous budget: continuousBudget = fuseRating*derating [A]
margin: margin = continuousBudget-operatingCurrent [A]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

operating current: 5 A
fuse rating: 10 A
derating: 0.75

Calculated

continuous budget: 7.5 A
margin: 2.5 A

Assumptions and limits

Operating current versus supplied derated fuse current; no trip-curve coordination solve.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Fuse and load-curve comparison. Inputs: load/inrush trace; fuse curves; conductor limits; source fault model. Outputs: time-current overlay; unresolved coordination conditions. Model scope: Conductor geometry and sourced installation/component limits. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: load/inrush trace, fuse curves, conductor limits, source fault model
Outputs: time-current overlay, unresolved coordination conditions
Modes: calculate, compare, sweep
Drawing: Harness and voltage-drop diagram

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS