Fuse let-through comparison calculator

Field use cases

Use this page when a fuse or protective-device record already has an energy value and the next task is to compare it with a withstand limit. It works well for cable review, equipment comparison and protection notes where the energy comparison must stay separate from the cable withstand worksheet.

The page is intentionally narrow. It does not choose a fuse, cable or device setting. It keeps the energy basis and withstand basis visible so a reviewer can trace the row back to the project file or manufacturer data.

Input basis

The fuse reference should identify the fuse, device or protection row. The let-through energy should come from manufacturer data, a project schedule or a competent-person record. The withstand limit should come from the cable or equipment basis being checked. Clearing time and prospective fault current keep the energy comparison traceable.

Review workflow

1. Identify the fuse or device reference.
2. Enter fuse let-through energy from the source record.
3. Enter the withstand limit from the cable or equipment record.
4. Enter clearing time and prospective fault current for the same point.
5. Review energy margin and energy utilisation.
6. Keep the source record and equivalent-current basis with the export.

Worked Australian examples

A protection record compares 900000 A2s fuse energy with a 1322500 A2s withstand limit using a 0.1 s clearing time basis. The energy margin is 422500 A2s, and the equivalent current is 3 kA.

A review row compares 1500000 A2s fuse energy with a 1322500 A2s withstand limit. The energy margin is -177500 A2s, so the fuse record and withstand source need review before the row is used.

A record comparing 2500000 A2s energy at 0.25 s exposes an equivalent current of 3.162 kA from the same energy basis. That current is a worksheet conversion only and does not replace the source record.

Boundary with related calculators

Use the I2t cable withstand calculator when the missing question is conductor thermal withstand from current, time and k value. Use the short-circuit current calculator when the missing question is prospective current. Use the breaker rating comparison calculator when the row needs rating and breaking-capacity comparisons as a separate worksheet.

Australian standards boundary

Fuse-energy comparison in Australia sits within wiring rules, equipment data, cable withstand data, manufacturer instructions and project documentation. This page names AS/NZS 3000 and AS/NZS 3008.1.1 as context, but it does not reproduce controlled tables or selection rules.

Equivalent current is shown because it helps a reviewer connect the energy basis to the current basis. It is not a fuse curve and it is not a final protection decision. State or territory requirements, local authority expectations, manufacturer data and competent-person review can override the worksheet basis.

Stop points

• The fuse reference cannot be matched to the project record.
• The withstand limit source is missing or unclear.
• Clearing time and fault current do not belong to the same point.
• Energy margin is negative.
• The worksheet is being used as fuse selection rather than comparison.