Site power quality basics

Many “charger faults” are feeder, transformer, or harmonic problems wearing an EVSE mask. This guide helps you separate site power from equipment before you condemn a power module. One healthy voltage check under load saves a crate of wrong parts.

You are not replacing the electrician. You are gathering enough evidence to stop shotgunning modules and to write a ticket that power people can act on.

When to use this guide

• Faults cluster at peak depot load or extreme heat
• Multiple brands/cabinets trip together
• Undervoltage / phase-loss / grid codes in logs
• Breaker trips but EVSE screen only says Faulted
• Sessions collapse only when many stalls ramp together
• After utility work, transformer tap change, or switchgear service

Related: power · grid · switchgear

How site power problems present

Clue	Points to site
Several stalls die in the same minute	Feeder / transformer / LMS
Only happens under high simultaneous kW	Voltage sag, tap, conductor heat
Recovers after utility event	Grid transient
Single gun, cable-dependent	Less likely site — look EVSE/cable
Phase-loss / undervoltage codes across OEMs	Shared AC
Lights dim / other site loads brown	Feeder / transformer
Breaker hot / smell at switchgear	Distribution, not SECC

Presentation false friends

Looks like	Often actually
Bad power module	Undervoltage under simultaneous ramp
Ground fault in one EVSE	Shared GF device or wet gear upstream
LMS bug	Real sag; LMS curtail is symptom or co-symptom
Random Faulted overnight	Utility switching / capacitor bank / storm
“Needs larger charger”	Undersized transformer for the depot as built
Harmonics “myth”	Sensitive upstream breaker nuisance with many rectifiers

Decision tree

1. One connector or many?
   MANY → site / LMS / cabinet DC bus
   ONE ↓
2. Voltage at cabinet under load in band?
   NO → electrician / utility path
   YES ↓
3. Protective device tripped upstream?
   YES → find why (overload, GF, arc flash) before reset spam
   NO ↓
4. Harmonics / PF / nuisance trips on sensitive breakers?
   → power quality study
5. LMS allocation zero while voltage healthy?
   → energy ops / LMS (see also OCPP Faulted triage)
6. Else return to EVSE-specific isolation/module triage

Ranked causes

1. Undervoltage under load — long feeder, undersized transformer, soft utility, loose lug heating under load.
2. Phase loss / imbalance — loose lug after service; single-phase load miswire on 3P gear; failed pole on upstream device.
3. Nuisance GF / breaker — shared neutrals, wet gear, wrong breaker type for EVSE inrush, series rating mistakes.
4. Harmonics from many rectifiers — older gear without adequate filtering; interaction with PFC stages.
5. LMS / demand response curtail interpreted as fault — confirm allocation before parts.
6. SPD end-of-life / surge aftermath — site event cleared, EVSE still latched Faulted.
7. True EVSE power stage fault — after site is proven healthy under comparable load.

Worked examples

Example A — Six stalls Faulted at 17:10 daily

Observed: Same clock time on workdays; feeder warm; CSMS undervoltage-ish vendor codes differ by brand but timestamps align.

Triage: Peak depot coincidence. Measure at cabinet under ramp (qualified person). Compare utility interval data.

Fix: Electrician/utility/transformer or load management — not six module RMAs.

Example B — Single stall Faulted; sister stall on same board fine

Observed: Same panelboard; only stall 3; cable-dependent sometimes.

Triage: Less likely shared feeder sag. Branch circuit, local disconnect, that EVSE, or cable.

Fix: Return to EVSE/cable triage; still verify lugs on that breaker.

Example C — After storm, island dead, breakers closed

Observed: Utility restored; EVSE show phase-loss or DC bus faults; SPD flags on gear.

Triage: Confirm actual phase presence under load; inspect SPD; don’t reset forever into a missing phase.

Fix: Utility/electrician if phase missing; then OEM clear procedures for latched EVSE faults.

Example D — Breaker trips on session start only when two guns on one cabinet run

Observed: Dual-gun cabinet; either gun alone OK; both → upstream trip.

Triage: Inrush + continuous current vs breaker curve; shared feeder limit; LMS should have prevented — check config.

Fix: Protection coordination / LMS caps / electrician. Don’t upsize breaker casually past conductor rating.

Example E — Neutral current high on 480Y system feeding chargers

Observed: Electrician finds unexpected neutral current; nuisance trips; odd imbalance.

Triage: Wiring error, shared neutrals, severe imbalance, or harmonic return paths.

Fix: Electrician investigation — EVSE tech documents which stalls were on and kW at time of measurement.

Field procedure

1. Ask ops: did the whole island drop or one stall? Exact time? Utility notice?
2. Read upstream breaker / relay targets; photograph positions; note which devices are shared.
3. Measure phase-phase and phase-ground at the cabinet while a session ramps (qualified personnel only).
4. Compare to nameplate and utility agreement / site one-line.
5. Thermal scan lugs and transformer under load.
6. Correlate CSMS fault timestamps with utility / BMS / LMS logs.
7. If sag confirmed → escalate electrician; do not shotgun modules.
8. After power restore, expect EVSE reboot and auth storms — clear Faulted with a checklist, validate under representative load.

Example expectations

Measurement	Notes
480 V class	Stay within site design tolerance under peak simultaneous kW
208/240 class	Same rule — percent sag matters more than idle nameplate
Neutral current	Unexpected current → wiring investigation
Drop session ↔ voltage dip	Strong site PQ signature
Imbalance	Multi-percent phase imbalance under load → lug/transformer/utility
Breaker temperature	Hot handle under load → investigate before “nuisance” label

Evidence checklist

• One-line / panel schedule referenced
• Scope: stall / island / site
• Timestamp alignment across CSMS + utility + LMS
• Photo of upstream device positions
• Under-load voltage (qualified) attached or scheduled
• Thermal images under load if available
• LMS allocation at time of fail
• Weather / ambient / depot occupancy note

Safety

Live measurements at EVSE gear are arc-flash exposures. Use appropriate PPE category for the gear. LOTO before retorquing lugs. Do not reset breakers into a known fault repeatedly. SPD replacement and switchgear work belong to qualified electrical workers. Assume feeders remain energized when an EVSE HMI is dark.

Weekend / after-hours notes

• Peak-hour failures often vanish at 02:00 with light load — schedule a witnessed peak retest; don’t close the ticket on a midnight “works now.”
• Utility switching windows show up as multi-site events — check neighboring depots before overnight module swaps.
• If you must restore partial capacity, use LMS/ops to cap simultaneous kW rather than defeating protection.
• Document temporary Unavailable stalls so day-shift power study isn’t fighting random driver retries.

Documentation template (ticket / handoff)

SITE / ISLAND / STALLS AFFECTED:
DATE/TIME OF EVENT(S):
TECH:
SYMPTOM SUMMARY:

SCOPE: single / multi-stall / multi-brand:
UPSTREAM DEVICES (IDs / positions / trips):
LMS STATE AT FAIL (amps allocated / curtail reason):
UTILITY EVENT KNOWN: yes/no/unknown

MEASUREMENTS (qualified person / PPE cat):
- Vab/Vbc/Vca idle:
- Vab/Vbc/Vca under ramp:
- Imbalance / neutral notes:
- Thermal findings:

CSMS CODES / TIMESTAMPS:
ONE-LINE REFERENCE:
ACTIONS TAKEN (incl. breaker resets — count them):
REQUESTED NEXT STEP: utility / electrician / PQ study / LMS ops / EVSE OEM

Additional failure modes

Mode	Field signature	Who owns it
Loose lug under load only	Idle voltage OK; sag + heat at peak; thermal camera hotspot	Electrician
Soft utility / long feeder	Multi-brand simultaneous collapse; utility interval confirms	Utility + site design
Wrong breaker curve	Trips on start; continuous current within cable rating	Protection coordination
Shared GF device nuisance	Wet weather cluster; mixed loads on one GF	Electrician
Capacitor bank switching	Brief multi-stall blip; recovers; timestamped	Utility / PQ study
Generator / temp power oddities	Maintenance window; frequency/voltage weirdness	Site electrical lead
LMS fighting undervoltage	Allocation cuts as voltage falls — both real	Energy ops + electrician
SPD after surge	Flags; EVSE latched; utility already restored	Electrician + EVSE clear procedure

Load-test discipline (qualified personnel)

Do not declare “voltage fine” from an idle reading after lunch when the failure happens at 17:00 with twenty stalls online. Either:

• Witness a peak-period measurement at the cabinet, or
• Correlate utility metering / PQ recorder data with CSMS timestamps, or
• Schedule a controlled multi-stall ramp with ops and an electrician present.

Idle nameplate voltage with no load is necessary but not sufficient.

What to photograph for the electrician ticket

• Panel schedule / one-line snippet (if allowed)
• Breaker / relay targets and any trip flags
• Lug / bus thermal images under load
• SPD indicator windows
• EVSE HMI codes with timestamps
• CSMS multi-stall event list for the same minute
• LMS allocation screenshot at fail time

Temporary mitigation (ops-approved only)

Mitigation	Use when	Do not
LMS simultaneous kW cap	Proven sag at peak	Raise breaker size past conductor rating
Stagger depot pull-out	Soft transformer	Defeat GF or ESTOP
Mark stalls Unavailable	Damaged gear / open phase	Reset into missing phase repeatedly
Wait for utility	Confirmed utility event	Shotgun modules overnight

Hands-on “site vs EVSE” proof summary

Evidence	Favors site	Favors EVSE
Multi-brand same timestamp	✓
Cable swap changes outcome		✓
Under-load voltage out of band	✓
Single stall, healthy voltage, vendor module code		✓
Sister stall same feeder OK under same kW		✓
Feeder breaker trip	✓

Peak-event timeline template (attach to ticket)

Use this when faults cluster at rush hour. Fill times in local, note UTC if CSMS uses it.

Time	Observation
T-30 min	Depot occupancy / LMS headroom
T-10 min	First stall warnings (if any)
T0	First Faulted / trip
T0+1 min	Count of stalls affected
T0+5 min	Upstream device state photographed
T0+15 min	Voltage under load attempted / deferred
Restore	What changed (utility, breaker, LMS cap)

Correlate with undervoltage and LMS entries after scrubbing site-only IDs for shared notes.

Quick field script (one page)

1. Scope: one stall or many?
2. Timestamp cluster?
3. Upstream device state photo
4. LMS allocation at fail
5. Idle voltage (qualified) — necessary
6. Under-load voltage at failure condition — decisive
7. Thermal lugs/transformer
8. Decide: electrician/utility vs EVSE OEM
9. Do not shotgun modules on multi-stall simultaneous events

If you only complete steps 1–4 overnight, that is still a valid handoff — better than six wrong RMAs.

Escalate when

• Utility voltage outside contract
• Transformer OT / oil / gas alarms
• Arc-flash relay operations
• Repeated phase-loss with tight lugs → deeper distribution issue
• Protection coordination unclear after expansion
• Harmonic / PF study needed for chronic nuisance trips
• Temporary power / generator feeding EVSE island → site electrical lead before EVSE OEM

Database: grid undervoltage · phase loss · LMS · SPD · transformer · harmonics · breaker trip

Related fault entries

• ABB-T54-GRID — Grid undervoltage trip
• GND-01 — Ground continuity fail at dispenser
• LOAD-01 — Dynamic load management caps to 0 A
• CAB-BUS — DC bus undervoltage
• PE-NB-GRID — Input phase loss