Insulation resistance record calculator

Insulation Resistance Boundary

Use this calculator after an insulation-resistance measurement has already been recorded and the next task is to summarise the row against a criterion supplied by the user. The worksheet does not choose a test voltage, create an Australian limit, decide whether an installation is ready to energise or replace the original instrument record.

The useful output is the difference between the measured resistance and the entered criterion. A positive margin can help a reviewer see that the entered value is above the comparison basis. A negative margin keeps the row open for review. In both cases, the source of the criterion matters as much as the arithmetic.

Inputs To Keep With The Record

The page is strongest when it travels with the same details as the original test sheet. Record the switchboard, circuit or asset reference, the test voltage, the measured insulation resistance, the criterion source and the number of circuits or rows covered by the entry.

A bare value such as 2.5 Mohm is not enough for another person to review later. The same value can have different meaning depending on test voltage, circuit grouping, connected equipment, environmental condition and the procedure used on site.

Worked Australian Examples

A distribution board handover row records four final circuits tested at 500 V. The measured insulation resistance is 2.5 Mohm, and the user enters a 1 Mohm criterion from the project record. The margin is 2.5 - 1 = 1.5 Mohm, and the utilisation is 2.5 / 1 x 100 = 250%.

A maintenance row records two circuits at 0.4 Mohm against an entered 1 Mohm criterion. The margin is -0.6 Mohm, and the utilisation is 40%. That row should remain open until the circuit condition, connected equipment, environmental condition and criterion source are reviewed.

An equipment row may use a different test voltage or criterion. The calculator can still perform the arithmetic, but the equipment procedure and manufacturer instructions decide whether those entered values belong together.

Review Workflow

Start from the record in front of you. Do not change the criterion simply to make the margin look better. If the row is unfavourable, keep the row visible and use the result to organise follow-up.

1. Identify the circuit, board, asset or test sheet row.
2. Copy the test voltage and measured insulation resistance from the record.
3. Enter the criterion only when its source applies to this row.
4. Check the margin and utilisation.
5. Record whether the row is ready for project review or needs investigation.
6. Keep the original instrument record, procedure and reviewer notes with the export.

Boundary With Other Protection Records

Insulation resistance is not the same as continuity resistance, fault-loop impedance, prospective short-circuit current or an RCD test row. Use the continuity resistance calculator when the record is about measured conductor continuity after lead compensation. Use the fault-loop impedance calculator when the starting value is loop impedance. Use the RCD test checker when the record is a residual-current device test row.

Keeping those records separate makes the job file easier to review. Each calculator owns one measurement question, one formula and one export record.

Australian Standards Context

Australian electrical testing records sit within current Wiring Rules, verification requirements, workplace procedures, local authority expectations and manufacturer instructions. AS/NZS 3000 and AS/NZS 3017 are named as context because insulation-resistance records belong in that verification environment.

This page does not reproduce controlled tables, test procedures, legal thresholds or equipment-specific instructions. The user enters the comparison criterion and keeps the source with the project record. State or territory requirements, workplace rules, manufacturer instructions and competent-person review can override the worksheet basis.