Guides for charging technicians

EV charger overheating: why an AV fleet depot connector runs hot and when to pull it from service

A hot connector is the charger protecting itself, a bad contact, or heat from outside. How to tell which, how hot is too hot, and the line where the stall comes out of service.

By XoomPark Editorial Team · November 8, 2026

A hot connector is one of three things. The charger is protecting itself after heavy back-to-back use, and it derates or stops on its own.¹ A contact has gone high-resistance: dirty, worn, bent or loosely terminated, and it heats at every session.⁵ Or the heat comes from outside: sun on the cable, dust in the cabinet. Pull the stall when the connector shows damage,⁷ when it runs more than 15 °C hotter than a similar connector at a similar load,⁶ or when it keeps hitting its over-temperature stop.

Six ways a connector shows heat, what each usually is, and what the technician does.
What you see	What it usually is	First check	Action
Full power for a few minutes, then a steep drop	Cable thermal limit on a busy stall²	Session history: how many full-power sessions back to back	Space sessions; check whether the limit clears on its own
Cable over-temperature derate or stop code	Cable or connector too hot¹	The logged temperature and current	Let it cool; vendor ticket if it repeats⁴
One connector hotter than its twin on the same dispenser	A high-resistance contact⁵	Thermal scan of both at similar load	Repair now if more than 15 °C hotter⁶
Discolored, pitted or bent pin, cracked housing	Contact or housing damage	Visual check before the shift⁷	Out of service until repaired and tested⁷
Whole cabinet hot, every connector slow	Ambient heat or blocked airflow¹	Sun, dust on filters, clearance around the cabinet	Clean, shade, restore airflow⁴
Limit stays after the car leaves	A latched thermal state that needs a reset²	The vendor's reset procedure	Reset per the manual; log it

How hot is too hot for a charging connector?

The charger decides, and its manual says where. Eaton's Green Motion DC charger raises an alarm when the connector reads 90 °C or more, clears it below 90 °C, and disconnects output and ends the session at 105 °C.⁴ Other makers set their own numbers; read the protection table in your charger's manual before you trust your hand.

The ChargeX Consortium's minimum required error codes give the same events a common name across vendors: CableOverTempDerate (CX018) when the cable or connector is hot enough that power is reduced, CableOverTempStop (CX019) when the session stops, and HighTemperature (CX003) when the heat is inside the charger.¹ Eaton's instruction for its own connector over-temperature code is to let the connector cool and call service if it persists.⁴

A derate is the system working. A stop that recurs on the same connector, with the same cars and the same weather, is a fault, and it belongs in the log by connector, not by stall.

Why does a DC cable run hot on back-to-back sessions?

Because current makes heat and a busy stall never gets to shed it. In a 2023 Idaho National Laboratory and Oak Ridge test, a 350 kW charger ran three full-power 10-minute sessions with 5-minute breaks. It held 346 kW for about 6 minutes, then the liquid-cooled cable hit its thermal threshold and the charger limited output to 90 A.²

The limit did not lift when the car left. It held through every later session until the lab cycled the charger's 480 V input power.² The cable was rated for 400 A continuous and 500 A peak,² and the test ran at 750 V DC. Our arithmetic: 90 A at 750 V is 67.5 kW, about a fifth of the power the stall delivered before the limit.

Liquid cooling is why a high-power cable can be handled at all. The Department of Energy's 2017 fast-charging gap assessment put the ceiling for convectively cooled cables at 250 A, and said a liquid-cooled cable and connector allow a constant 350 A with short events up to 400 A.³ A depot that turns cars through one stall all night runs that cooling harder than a highway site where cars arrive one at a time.

Which checks find a bad contact before it fails?

A look before every shift and a thermal scan under load. The Federal Energy Management Program's maintenance guide explains that a loose or corroded electrical connection runs abnormally hot because of increased resistance, and that an infrared camera shows the pattern before the connection is hot enough to fail.⁵

Look at the pins, the housing, the latch and the first metre of cable before the shift: loose parts, deformed or missing pins, a damaged jacket.⁷
Keep the connector clean and dry. Eaton's manual says to wipe dirt with a cloth and mild detergent and never to touch the terminals while powered.⁴
Scan connectors at similar load and compare like with like. The Bureau of Reclamation recommends inspecting at the highest load available and never below 40% of rated, and waiting 45 minutes after a load change for temperatures to settle.⁶
Note the wind. Reclamation's example shows the same connection reading a 50 °C rise in a 3 to 5 mph breeze and 100 °C in still air.⁶ An outdoor stall read on a windy night looks healthier than it is.
Clear cabinet dust. Eaton calls for removing dust from the cabinet monthly so the charger can shed its heat.⁴

NETA severity criteria for electrical connections, as published in the Bureau of Reclamation's thermal analysis manual.
Rise over ambient	Rise over a similar part	What it means
1 to 10 °C	1 to 3 °C	Possible deficiency: monitor and repair when possible⁶
11 to 20 °C	4 to 15 °C	Probable deficiency: investigate further and repair when possible
21 to 40 °C	Not listed	Deficiency: repair at next opportunity
More than 40 °C	More than 15 °C	Major deficiency: repair immediately

Reclamation notes these are guidelines in the absence of consensus standards, and that heating rises with the square of current,⁶ so record the current next to every reading. A dual-cable dispenser gives you a built-in reference: two connectors, same cabinet, same weather.

When does a hot connector come out of service?

When it is damaged, when the scan says repair now, or when the over-temperature stop keeps coming back. OSHA's rule for cord- and plug-connected equipment requires a visual check before use on each shift and says a damaged item that might injure an employee is removed from service until repairs and tests make it safe.⁷

That OSHA paragraph is written for portable cord- and plug-connected equipment; a charger's fixed cable may sit outside its letter. We apply the same rule to every charging connector because the hazard is the same. Eaton's manual goes further for its own unit: it prohibits using the charger when the connector or cable is defective, cracked or worn, or when internal wiring shows.⁴

Pulling a connector is the technician's call; replacing one is not. Opening the dispenser means deenergizing it, and OSHA allows only qualified persons to work on parts that have not been deenergized.⁸ Eaton reserves servicing for qualified personnel.⁴ Tag the stall out on the dashboard and in the yard plan so no car is routed to it.

How should a depot log connector heat?

By connector, with the temperature, the current and the session count. The Alternative Fuels Data Center lists periodic parts checks, clean equipment and secure cable storage as routine charger maintenance, and says a maintenance contract should name a response time, a repair time and an uptime requirement.⁹

A log that reads "stall 4, overheat" cannot hold a vendor to any of those. One that reads "stall 4 connector B, CX018 at 340 A, third full-power session in 25 minutes, 31 °C ambient, twin connector 12 °C cooler" can.

We worked three back-to-back sessions on a 350 kW stall

If a depot stall behaves like the one INL tested, three back-to-back 10-minute sessions deliver about 62 kWh instead of the 173 kWh full power would give, roughly 36%, with no fault that takes the stall offline.

Our method: INL's pattern of 346 kW for 6 minutes, then 90 A at 750 V for the rest of the test,² which we take as 67.5 kW. First session: 34.6 kWh at full power plus 4.5 kWh limited. Second and third: 11.25 kWh each. Full power for all 30 minutes would be 173 kWh. The fix is not a technician's; it is the schedule. Spread full-power sessions across stalls, and find out from the vendor whether your charger clears its thermal limit on its own or, like the unit INL tested, holds it until power is cycled.

When these checks are the wrong tool

The heat is inside the cabinet. A HighTemperature code points at the charger's own electronics,¹ and opening the cabinet is a lockout job for a qualified person.⁸
The same car runs hot on every stall. A cable stop can be the car's side; ChargeX classes CX019 as charger or car.¹ Log it against the car.
There is smoke, melting or a smell of burning. Hit the emergency stop and treat it as an incident, not a maintenance ticket.
The stall is under a vendor service contract. Thermal scans inside the dispenser are the vendor's work; send them your readings from the outside.

If a stall is out of service for a repair, the cars can charge elsewhere. XoomPark arranges AV fleet charging at existing stations in the hours their stalls sit unused, never blocks a station's regular customers and never pushes the station past its monthly peak.

Questions charging technicians ask

Is it normal for a DC charging handle to feel warm?

Warm under load, yes; the cable carries hundreds of amps and the charger watches its own temperature. Eaton's Green Motion alarms at 90 °C and stops at 105 °C,⁴ so the charger acts long before a handle is too hot to hold. A handle noticeably hotter than its twin at the same load is the one to scan.

Why did the charger slow down halfway through a session?

Either the car is tapering as it fills, or the cable hit its thermal limit. In INL's test the cable limit cut a 350 kW stall to 90 A after about 6 minutes of back-to-back use.² The charger log will show a cable over-temperature code if it was the cable.¹

Does a thermal derate clear by itself?

It depends on the charger. Eaton's connector alarm resets when the temperature falls below 90 °C;⁴ the unit INL tested held its 90 A limit until its input power was cycled.² Check your manual and note which kind you have.

How often should connectors be inspected?

Visually before each shift, which is OSHA's rule for cord- and plug-connected equipment.⁷ Thermal scans: Reclamation recommends an annual survey of electrical equipment and more often where loss experience or load warrants it,⁶ and a depot running stalls all night warrants it.

Can a technician replace a charging connector?

Only if the vendor's manual allows it and the person is qualified. Eaton reserves servicing for qualified personnel,⁴ and any work inside the dispenser starts with the supply deenergized.⁸

Sources

Sources are public. XoomPark isn't affiliated with the companies referenced in this post.

Authorship

Written by XoomPark Editorial Team in collaboration with Claude Opus 5.5

Role breakdown: Topic selection and publishing by XoomPark Editorial Team; research, source checks against primary sources and draft prose by Claude Opus 5.5.