Industrial Connectors: A Selection Guide by IP Rating, Current Rating, and Number of Poles

Choosing the wrong connector costs more than a re-spin — it costs field downtime, safety recertification, and lost production. This guide breaks industrial connector selection into three decisions: environmental sealing (IP rating), electrical capacity (current per contact), and signal/power topology (number of poles). Pick these three correctly, and the rest follows.

Step 1: Match the IP Rating to Your Environment

The IP (Ingress Protection) code has two digits: the first covers solid particle ingress, the second covers liquid ingress. For industrial connectors, only a handful of ratings matter in practice.

IP Rating	Dust protection	Water protection	Typical application	Connector families
IP44	Objects ≥ 1 mm	Splashing water, any direction	Indoor control cabinets, protected machinery	HARTING Han A, Weidmüller RockStar
IP65	Dust-tight (no harmful deposit)	Low-pressure water jets (6.3 mm nozzle)	Factory floor sensors, conveyors, packaging machines	M12 A-coded, M8, DIN 43650 valve connectors
IP67	Dust-tight (complete)	Temporary immersion (1 m, 30 min)	Outdoor enclosures, agricultural equipment, marine topside	M12 X-coded, M23 signal/power, MIL-DTL-5015
IP68	Dust-tight	Continuous immersion (depth/time per manufacturer)	Submersible pumps, underwater sensors, offshore subsea	Custom-molded circular, glass-to-metal sealed
IP69K	Dust-tight	High-pressure, high-temperature jets (80 °C, 80–100 bar)	Food & beverage washdown, pharmaceutical CIP	Stainless-steel M12/M23, EPDM/FKM seals

Critical nuance: IP67 and IP68 are not hierarchical. A connector rated IP68 for 2 m / 24 h may fail an IP67 jet test if its seal geometry is optimized for static pressure, not directional spray. Specify both test conditions when the environment alternates between washdown and submersion.

Step 2: Size the Current Rating per Contact

Current ratings are specified at a standard ambient temperature — typically 40 °C. Derating applies when multiple contacts carry full load simultaneously, because contact resistance heating accumulates inside the housing.

Current per contact	Contact diameter	Wire gauge (Cu)	Connector examples
2–4 A	0.6–0.8 mm	0.14–0.34 mm² (AWG 26–22)	M8 sensor, M12 A-coded signal
6–10 A	1.0–1.6 mm	0.5–1.5 mm² (AWG 20–16)	M12 A-coded power, M23 6-pole, HARTING Han E 16 A
16–35 A	2.5–3.6 mm	2.5–6.0 mm² (AWG 14–10)	HARTING Han C/D, M23 high-power, MIL-DTL-38999 size 16
40–100 A	5.0–8.0 mm	10–25 mm² (AWG 8–4)	HARTING Han HPR, Amphenol SurLok Plus, Anderson Powerpole
100–200 A	10–14 mm	35–70 mm² (AWG 2–2/0)	HARTING Han HC Modular, single-pole circular

Derating rule of thumb: derate by 20 % for 3–6 poles, 40 % for 7–12 poles, and 60 % for 13+ poles when all contacts carry rated current. The housing material (metal vs. thermoplastic) significantly affects heat dissipation — consult the manufacturer's derating curve.

Step 3: Choose the Number of Poles (and Coding)

Pole count defines what the connector carries: power, signal, data, or a mix. The coding letter (A, B, D, X, etc.) on M12 and M23 connectors prevents accidental mating of incompatible circuits.

Application	Poles	Coding	Speed / Voltage
DC sensor/actuator (3-wire PNP/NPN)	3–4	M12 A-coded	24–250 V DC, 4 A
PROFINET / EtherNet/IP	4	M12 D-coded	100 Mbps (Cat 5e)
Gigabit Ethernet	8	M12 X-coded	1–10 Gbps (Cat 6a/7)
CAN bus / DeviceNet	5	M12 A-coded (custom pinout)	500 kbps–1 Mbps
Servo motor power + brake	6–9	M23 / M40 power	400–630 V AC, 35 A
Hybrid (power + signal)	4+2 or 4+4	M23 hybrid	600 V / 10 A + signal

Hybrid connectors — combining large power contacts with small signal contacts in one housing — reduce cabinet penetrations but require careful signal routing: power return paths must not share a connector with low-level analog signals unless internal shielding barriers are present.

Connector Material and Plating: The Silent Decision

Contact material and plating determine corrosion resistance and mating cycle life:

Brass + gold (0.8 µm Au over 2 µm Ni): signal contacts, dry environments, up to 500 cycles. The nickel underplate is mandatory — gold without it diffuses into brass within months at elevated temperature.
Copper alloy + silver: high-current contacts (16 A+), up to 100 cycles. Silver oxide is conductive and self-healing; silver sulfide is not. Avoid near rubber processing or paper mills.
Stainless steel 303/316 + PVD coating: food-grade, CIP/SIP compatible, 1,000+ cycles. Required for IP69K in hygienic environments.

FAQ

What is the difference between IP67 and IP68 for connectors?

IP67 guarantees temporary immersion — 1 m for 30 minutes. IP68 means continuous immersion, but depth and duration are manufacturer-specified (3 m / 24 h, 10 m / 7 days, etc.). An IP68 connector is not automatically IP67-compliant; the test methods differ, and some IP68 products fail directional jet tests. Specify both ratings when washdown and submersion both apply.

How many poles for a 3-phase motor connection?

Four poles minimum: L1, L2, L3, PE. With a brake: add 2 poles (24 V DC coil). With a PTC thermistor for winding temperature: add 2 signal poles. Total: 8 poles for a typical servo motor — covered by M23 8-pole or M40 hybrid connectors.

Can I use an M12 connector for power instead of signal?

Yes, with the right coding. K-coded handles 630 V AC / 16 A (5 poles: L1, L2, L3, N, PE); S-coded handles 630 V AC / 16 A (4 poles: L1, L2, L3, PE). Do not use A-coded M12 for power beyond 4 A — the 0.8 mm contact diameter is undersized for continuous current, and the connector lacks arc testing for inductive load breaking.

Does the housing material matter for EMI?

Yes. Metal housings (zinc die-cast, aluminum, stainless steel) provide 360° shielding when mated to a shielded cable with the braid terminated to the shell. Plastic housings offer no shielding without an internal metallized coating or shield ring. For CAN bus, Ethernet, or any data link above 1 Mbps in an industrial environment, a shielded metal housing is the difference between error-free communication and intermittent CRC failures.

Find the Right Connector for Your Application

Industrial connector selection reduces to three data points: IP rating, current per contact, and pole count. Novapart stocks M8/M12/M23/M40 circular connectors, heavy-duty rectangular connectors (HARTING Han, Weidmüller RockStar), and MIL-spec circulars — filterable by IP class, current rating, pole count, and coding. Browse the connectors category to narrow by your parameters, or submit a technical inquiry and our engineering team will cross-reference your requirements against available inventory.

Suggested internal links:

Browse all industrial connectors — filter by IP rating, manufacturer, current, and poles.
Explore connectors by manufacturer — compare HARTING Han, Amphenol, TE Connectivity, and Phoenix Contact.
Cross-reference tool — enter an MPN from any manufacturer to find compatible alternatives.