Mean Time To Repair (MTTR) is the average time required to restore an asset to normal operation after a failure occurs. In EV charging, MTTR measures how quickly a charger (or a site) is returned to service once a fault is detected, including diagnosis, travel, access, repair actions, testing, and recommissioning.
What Is MTTR?
MTTR is a reliability and operations KPI used to evaluate maintenance effectiveness. It is typically calculated as:
– MTTR = Total repair time for failures ÷ Number of repairs
“Repair time” may include only hands-on work, or it may include end-to-end downtime from fault detection to service restoration—this depends on how the operator defines it. For EV charging networks, the end-to-end definition is often the most meaningful because it matches user impact and uptime.
Why MTTR Matters in EV Charging
Low MTTR improves charger availability and reduces operating cost. It matters because it:
– Increases uptime and improves user experience
– Helps meet SLA targets for public and commercial charging
– Reduces lost charging revenue and penalty risk
– Improves fleet readiness in depot and workplace charging
– Highlights process bottlenecks such as poor access, missing spares, or slow diagnostics
MTTR is especially important for locations with high utilization, where each hour of downtime has a large operational impact.
What Typically Drives MTTR Up or Down
Common contributors that increase MTTR
– Limited maintenance access (blocked service doors, locked rooms, no isolation access)
– Long travel time or restricted service windows
– Missing documentation (no as-built drawings, unclear breaker mapping)
– Spare parts not available (connector assemblies, contactors, PCBs)
– Intermittent faults requiring repeat site visits
– Poor remote visibility (no OCPP telemetry, weak connectivity)
Common contributors that reduce MTTR
– Remote diagnostics and clear fault codes via CPMS
– Standardized hardware and repeatable service procedures
– Pre-agreed site access (keys, permits, gate control)
– On-hand spares kits and fast logistics
– Good installation quality and protection coordination
– Clear labeling and commissioning documentation
MTTR in EV Charger Operations
MTTR is used to:
– Compare performance across sites, installers, or charger models
– Identify the highest-impact failure types (e.g., connector wear vs communication faults)
– Optimize preventive maintenance frequency and spare parts strategy
– Improve service workflows and reduce repeated call-outs
– Support procurement decisions based on lifecycle cost, not only CAPEX
MTTR vs MTBF
MTTR (repair speed)
– How long it takes to restore service after a failure
MTBF (Mean Time Between Failures)
– How often failures occur over time
A reliable charging network targets both: fewer failures (higher MTBF) and faster repairs (lower MTTR).
How MTTR Is Commonly Reported
– Per charger (individual asset)
– Per site (combined availability of multiple chargers)
– By fault category (power, communication, payment, connector, vandalism)
– By severity (full outage vs partial connector outage on a dual-port charger)
– As part of SLA metrics (e.g., “restore within 24 hours”)
Related Glossary Terms
Uptime
Availability
Service level agreement (SLA)
O&M (Operations and maintenance)
Charger diagnostics
OCPP
Preventive maintenance
Mean Time Between Failures (MTBF)
Maintenance access planning
Maintenance cost reduction