Device coordination worksheet calculator

Entered coordination points

Use this worksheet when a protective-device record already has one current point and two device times. The row should identify the upstream device, downstream device, current basis, upstream clearing time, downstream clearing time and the entered minimum separation used by the reviewer.

The calculation is intentionally narrow. It subtracts downstream time from upstream time, then subtracts the entered minimum separation. A positive margin means the entered point has time separation above the entered value. A negative margin means the row needs device-data review before it is carried into project records.

Review workflow

1. Confirm the upstream and downstream devices refer to the same circuit path.
2. Enter the same fault-current point for both devices.
3. Enter the upstream clearing time from the applicable device record.
4. Enter the downstream clearing time from the matching source basis.
5. Enter the minimum separation value being used for the worksheet row.
6. Review time separation, separation margin and overlap flag together.
7. Keep the source curve record beside the exported worksheet.

Do not combine this row with breaking-capacity, cable withstand or device-energy checks. Use the related calculators when those values need a separate record.

Formula basis

The worksheet uses three visible relationships:

The calculator does not infer curve shape between points. If the current point, device setting or manufacturer curve changes, enter a fresh row rather than stretching the old result.

Worked Australian examples

A switchboard worksheet compares MSB-MCCB-1 and DB-MCB-4 at 6 kA. The upstream time is 0.18 s, the downstream time is 0.04 s, and the entered minimum separation is 0.05 s. Time separation is 0.14 s, so the margin above the entered separation is 0.09 s.

An overlap row uses upstream time 0.08 s and downstream time 0.10 s at the same 6 kA point. Time separation is -0.02 s, so the overlap flag remains visible and the row needs device-data review.

A margin-sensitive row uses upstream time 0.08 s, downstream time 0.04 s and entered minimum separation 0.05 s. Time separation is positive at 0.04 s, but the separation margin is -0.01 s, so the source record still needs review.

Coordination worksheet boundary

This page is not a manufacturer curve tool. It does not draw time-current curves, digitise curves, interpolate between points, select settings, choose products or close detailed curve coordination work. It records a single entered current point and the time separation that follows from values supplied by the user.

Manufacturer data remains controlling

Protective-device behaviour depends on the exact product, curve, setting, temperature conditions, tolerance, installation context and upstream network basis. Australian project records also sit inside current standards, local authority expectations, DNSP conditions where relevant and switchboard documentation.

The worksheet result is useful because it keeps the arithmetic visible. It is not useful when the current point is guessed, the two device times come from different bases, or the source curve record cannot be traced. Keep the manufacturer record and reviewer basis with every exported row.

Stop points

• The upstream and downstream time values do not come from the same current point.
• The device reference cannot be matched to the switchboard or circuit schedule.
• The minimum separation value has no reviewer basis.
• Device settings, manufacturer curves or source data have changed since the row was prepared.
• Cable withstand, breaking capacity, let-through energy or arc-flash review also needs a separate record.