IP66 vs IP67 on an On-Board Charger: What the Second Digit Really Covers

The IP rating on an on-board charger is two numbers doing two different jobs. The first digit is dust and foreign-object protection; the second is water. IP66 and IP67 differ only in that second digit — and the difference is narrower than the marketing suggests, because IP67 describes short-term immersion and says nothing at all about the pressure washing, steam cleaning and thermal cycling that actually kill chargers in the field.

Reading the two digits

The first digit runs 0–6. For vehicle power electronics only two values matter: 5 (dust protected — some ingress permitted, no harmful deposit) and 6 (dust tight — no ingress at all). Almost every automotive-grade charger claims 6, and it is verified in a dust chamber with talc.

The second digit runs 0–9K. The values you will see on charger datasheets:

Code	Test	What it means in a vehicle
IPX4	Splashing water from any direction	Rain and road spray only; not for underbody mounting
IPX5	6.3 mm nozzle, 12.5 L/min, 3 m	Hose-down in a service bay
IPX6	12.5 mm nozzle, 100 L/min, 3 m, 3 minutes	Powerful jets, heavy spray, deck wash on a boat
IPX7	Immersion, 1 m, 30 minutes	Short-term flooding, fording at low depth, wash-bay puddles
IPX9K	High-pressure, high-temperature jets (80 °C, 80–100 bar)	Steam cleaning and industrial wash lines

Why IP67 is not automatically the better choice

A fully potted unit can legitimately claim IP67. A fan-cooled unit usually cannot, because the air path is an opening. That pushes the decision back to thermal design: potting buys ingress protection at the cost of serviceability and, often, of continuous power. A 6.6 kW charger that is potted into a sealed block has to move its heat through the baseplate; if the mounting surface is not flat and thermally bonded, the unit derates or fails, and the IP rating will not save it.

The honest framing is that IP rating and thermal architecture are the same decision. Grapcharger’s 700 W unit is fanless and IP66 — no fan, no filter, convection and conduction only. The 850 W unit is potted to IP67 for installations where the charger sits low on the chassis or on a deck. Both are correct answers to different questions.

What IP codes do not cover

Four failure modes dominate in service, and none of them appear in an IP test:

Pressure washing with detergent. The jet is aggressive and the surfactant lowers surface tension, so water finds paths that a clean-water test never exposes. IPX9K is closer than IPX6, but it is still a laboratory nozzle.

Thermal cycling with condensation. A sealed housing that heats to 80 °C and cools to −20 °C pulls a partial vacuum. Without a membrane vent, the pressure differential works on every seal and every cable gland. A vent keeps the housing at atmospheric pressure and is compatible with IP67 — its absence is what fails, years later.

Salt fog and de-icing brine. Corrosion of the connector shell and mounting hardware, covered by ISO 9227 rather than IP.

Installation damage. A pinched O-ring or a cable gland tightened to the wrong torque converts an IP67 design into an IP44 installation. This is why mounting instructions belong in the qualification pack.

How to specify it

State the mounting location, the cleaning regime, the ambient temperature range and the expected service life, then let the supplier propose the construction. A useful RFQ line: “Unit is mounted under the vehicle floor, exposed to road spray, washed with a pressure washer twice a year, ambient −20 °C to +45 °C, 8-year life. Specify IP rating, venting, connector sealing and the corrosion test performed.” That produces a defensible answer. “IP67 please” produces a label.

The FAQ page covers the warranty and test-report questions that usually follow, and the thermal management note goes deeper on the cooling half of the same trade-off.

Frequently asked

Is IP67 better than IP66 for an on-board charger?

Only if the installation actually risks immersion. IP67 adds a 30-minute immersion test but does not add resistance to pressure washing, steam or salt. For a road-spray installation, IP66 with a membrane vent and a sealed connector is frequently the more durable design.

Can a charger with a cooling fan be IP67?

Not with the fan drawing air through the housing. A sealed liquid-cooled or conduction-cooled unit can be IP67; a forced-air unit cannot, because the air path is a continuous opening.

Does IP67 mean the unit can be submerged while operating?

No. The standard test is immersion of a non-operating or specified-state sample for 30 minutes at 1 m. Continuous operation underwater is a different requirement and needs a purpose-built housing.