Relay Contact Life Calculator

Work out relay contact life instantly with clear inputs, formula shown and shareable results.

About Relay Contact Life Calculator

Contact life falls steeply with load current — roughly as the inverse 1.5 power — and depends heavily on load type. Inductive loads cut life to around a third of resistive because the arc on break is far more energetic, and lamp inrush is worse still.

Formula

Contact life

life = rated operations x (rated current / load current)^1.5 x load type factor

Worked example

With the default values below, Relay Contact Life Calculator returns Expected operations of 75,308. Change any input above and every figure here is recalculated in your browser.

Inputs used

Rated electrical life: 100,000 operations
Load current: 6 A
Rated contact current: 10 A
Load typeone of Resistive, Inductive (AC-15 / DC-13), Lamp / capacitive inrush, Motor: Inductive (AC-15 / DC-13)

Results

Expected operations: 75,308 operations
Combined derating factor: 0.7531 x
Years at one operation per hour: 8.60 years
Load type factor: 0.350 x

Step by step

1Values used
2Contact life
3Expected operations= 75,308 operations
4Combined derating factor= 0.7531 x
5Years at one operation per hour= 8.60 years
6Load type factor= 0.350 x

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why do inductive loads destroy contacts?

Interrupting current in an inductance produces an arc that transfers metal from one contact to the other. Freewheel diodes on DC and RC snubbers on AC greatly extend life.

Should I use a contactor or a solid-state relay?

For frequent switching of inductive loads, a solid-state relay has no contacts to erode. The trade is on-state voltage drop, heat and no galvanic isolation of the load.