Electrical Spare Parts Inventory Planner
Estimate how many spare parts to hold when equipment quantity, expected failures, replenishment time and equipment criticality all influence the risk of being without a replacement.
Estimate a spare-stock target
Spare-stock recommendation
How the spare target is estimated
The planner estimates expected annual failures from installed quantity and an assumed failure rate. It then scales that exposure to the replenishment lead-time window. A criticality multiplier lets you intentionally hold more stock for equipment where downtime is particularly costly or the item is difficult to source.
Expected failures = Installed quantity × Failure rate × Review horizon
Lead-time exposure = Annual failure rate × Installed quantity × (Lead time ÷ 12)
The criticality-adjusted target is the ceiling of lead-time exposure multiplied by the criticality factor, bounded by the minimum spare floor.
Important interpretation
This is an inventory-planning heuristic, not a reliability-engineering prediction. Failure rates should come from maintenance history, OEM information or another defensible source. The model also assumes that one spare can replace one failed item and does not model repair turnaround or shared spares across multiple sites.
When to use a higher factor
A higher factor can be reasonable as a deliberate business rule for highly critical loads, long procurement cycles or equipment that would cause disproportionate operational disruption when unavailable. The factor should be documented so procurement and maintenance teams know why it was chosen.
FAQs
Why is the failure rate required?
The tool needs some estimate of expected replacement exposure. Without a failure assumption, any spare quantity would be arbitrary.
Why is criticality a multiplier?
Two identical-looking items can justify different stock strategies when one supports a critical process and the other does not.
Does the planner include repairable spares?
No. It treats the spare quantity as replacement stock for failed installed items.
Can the minimum spare floor be zero?
Yes. Enter zero when the policy does not require a minimum physical spare.