EV Charger Faults Only When The Dryer Runs Decision Tree

Why this matters

An EVSE (electric vehicle charger) that charges fine until the electric dryer starts and then faults out is reporting an interaction between two heavy 240V loads, and the cause is one of three specific things: a service or feeder approaching capacity that sags voltage low enough to trip the EVSE undervoltage protection, a shared or compromised neutral/ground path that lets one appliance's current leak into the other's ground-fault sensing, or an actual EVSE self-protection ground fault triggered by the dryer's motor or moisture. Each has a different fix, and the wrong one (telling the customer to upsize the service when the real issue is a shared neutral) is expensive and wrong. The EVSE's own fault code is the first clue, and most chargers log undervoltage, ground fault, and over-temperature distinctly.

Symptom presentation

The customer reports the EV charger stops or faults specifically when the clothes dryer is running, then resumes once the dryer stops. Pull the EVSE fault history: a CCID (charging circuit interrupting device) ground-fault trip, an undervoltage/brownout fault, and an over-temperature fault point in three different directions. Ask whether the EVSE and dryer share anything (same subpanel, adjacent breakers, a load-management device), the service size, and whether the dryer is a heat-pump (lower draw) or a resistance dryer (heavy 240V heating element).

Quick checks before isolation

Read the EVSE fault log first; it usually names the cause. Clamp the service main conductors and the EVSE feeder with both loads running and compare to the service rating - a 100A service running a 48A EVSE plus a 30A dryer plus baseline is genuinely near capacity. Measure EVSE supply voltage at the unit with the dryer off, then with the dryer on; a drop into the low 200s on a 240V supply explains an undervoltage fault. Confirm the EVSE is on its own dedicated circuit with its own neutral (if required) and EGC, not sharing a neutral or ground path with the dryer.

Isolation tree

Step 1 - Read the fault code. An undervoltage or brownout fault sends you to Step 2 (voltage sag). A ground-fault/CCID trip sends you to Step 3 (leakage path). An over-temperature fault sends you to Step 4 (connection heating). If the EVSE only stops with no logged fault, it may be obeying a load-management device that is correctly throttling - verify any energy-management or load-sharing setup before chasing a wiring fault.

Step 2 - Voltage sag / capacity. With the dryer running, measure EVSE supply voltage at the unit and clamp the service main. If voltage sags below the EVSE minimum (commonly around 200V) and service current approaches the rating, the service or feeder is overloaded - the fix is load management (a current-sensing load controller that throttles the EVSE when the dryer runs) or a service upsize, not an EVSE repair. If voltage sags hard but service current is modest, suspect a high-resistance connection on the shared feeder or service neutral (cross-reference the under-load voltage-drop tree) causing the sag.

Step 3 - Ground-fault / leakage path. A CCID trip means the EVSE sensed current imbalance between its conductors. Check whether the EVSE and dryer share a neutral or have a neutral-ground bond downstream of the service: dryer current returning on a path the EVSE monitors will register as leakage. Confirm the EVSE circuit has its own dedicated EGC and, if a neutral is present, a dedicated neutral with no downstream bond. Also rule out moisture in a garage-mounted EVSE that only crosses the trip threshold when the added dryer load slightly shifts ground potential. Megger the EVSE branch ground path.

Step 4 - Over-temperature. An over-temperature fault means a connection in the EVSE supply path is heating, and the added system load tips it over the thermal threshold. Inspect and torque-check the EVSE breaker lugs, the hardwire or NEMA 14-50 receptacle terminations (loose 14-50 receptacles are a known EVSE fire and fault source), and the feeder. A discolored receptacle or lug confirms it.

Confirming the diagnosis

A confirmed capacity/sag fault shows EVSE voltage dropping below its minimum and service current near the rating only when both loads run, clearing when load management throttles the EVSE or the service is upsized. A confirmed leakage fault shows the CCID trip correlating with a measurable shared-neutral or downstream-bond current path, clearing when the EVSE gets a dedicated neutral/ground with no downstream bond. A confirmed over-temperature fault shows a hot, often discolored termination that resolves on re-termination or receptacle replacement.

Remediation

For a capacity issue, install a listed load-management device per NEC 625.42 that limits the EVSE when other loads run, or upsize the service per a load calculation; do not simply ignore the fault. For a leakage path, give the EVSE a dedicated circuit with its own EGC (and neutral only if the unit requires it), and remove any downstream neutral-ground bond. For over-temperature, re-terminate to torque spec and replace any heat-damaged NEMA 14-50 receptacle with an industrial-grade device rated for continuous EVSE duty (hardwiring is preferred for 40A-plus continuous chargers). Re-test by running the dryer and EVSE together and confirming no fault.

References

• NEC 2023 Article 625 - Electric Vehicle Power Transfer System
• NEC 2023 Article 625.42 - EVSE rating and energy management / load control
• NEC 2023 Article 220 - Branch-circuit, feeder, and service load calculations
• NEC 2023 Article 250.6 - Objectionable current over grounding conductors
• UL 2594 - Standard for Electric Vehicle Supply Equipment