LMS heartbeat lost — failsafe curtail

How it presents

Symptom

LMS heartbeat lost — failsafe curtail — chargers derate or go Unavailable when site LMS/PLC heartbeat drops, protecting the feeder. protocol field note: keep evidence scrubbed and prove the ranked cause before module RMA on LOAD-02.

Root causes (by observed frequency)

1. #1 LMS PLC offline or network path to chargers down

   Failsafe is working

2. #2 Wrong LMS IP/VLAN after switch change
3. #3 Heartbeat timeout set too tight for loaded network
4. #4 Charger LMS client fault after FW update

Diagnostic procedure

1. 1. Read LMS online status and allocated amps

   Expected: Offline → failsafe amps

   Tools: LMS

2. 2. Ping/path-check LMS from charger VLAN

   Expected: Reachable

   Tools: IT

3. 3. Verify charger LMS client config (IP, ID)

   Expected: Matches commissioning

   Tools: HMI

4. 4. Restore PLC/network; watch amps recover

   Expected: Budget returns

   Tools: LMS

5. 5. Only then chase single-stall EVSE faults

   Tools: field

The fix

Failsafe curtail on lost LMS heartbeat is site controls — restore LMS before EVSE RMA.

1. Treat pad-wide curtail as LMS/network until proven otherwise.
2. Restore LMS PLC and VLAN path. Document readings and scrubbed photos for LOAD-02 before closing the ticket.
3. Correct charger LMS client settings after switch/FW changes.
4. Retune heartbeat timeouts with controls engineering if flapping.
5. Validate allocated amps and a live session after restore.