Introduction

A customer called us frustrated. Their outdoor equipment – a set of monitoring sensors deployed along a coastal industrial site – had been failing intermittently for months. The symptoms were maddening:

• Sensors would work perfectly for weeks, then suddenly drop out.

• Failures always seemed to happen after a cold night by a warm morning.

• Replacing the “waterproof” connectors seemed to fix the problem – temporarily. Within a few months, the same issues returned.

The connectors were rated IP68. They passed every lab test. The customer had even sent samples back to the original manufacturer, who declared them “within specification.”

So why were they failing?

We were called in to find out.

Step 1: The Initial Investigation

Our first step was to get our hands on one of the failed connectors – still installed, untouched, exactly as it had failed.

What we saw on the outside:

• Housing intact – no cracks, no visible damage.

• Cable gland properly tightened – no obvious gaps.

• Coupling nut secure – no cross-threading.

• No signs of external water exposure – the connector was dry to the touch.

Everything looked perfect. The connector appeared to be doing its job.

What we saw when we opened it:

Inside, we found something unexpected. The connector wasn’t full of water – but it wasn’t dry either. There was a fine film of moisture on the internal surfaces. The pins showed faint green discoloration – the early stages of corrosion. And on the inside of the housing, there were tiny water droplets – condensation.

Step 2: Understanding the Mechanism – Thermal Cycling and “Breathing”

To understand why this connector was failing, we had to look beyond the IP rating.

The equipment was located in a coastal area with significant daily temperature swings. Days were warm (25–30°C); nights were cool (10–15°C). The equipment itself also generated heat during operation and cooled down when idle.

Here’s what was happening:

This is called the “breathing effect” or thermal pumping. It’s a phenomenon where temperature changes cause the connector to alternately expel and inhale air through tiny, otherwise invisible gaps.

In this coastal environment, the outside air contained salt spray and high humidity. Each night, the connector inhaled a small amount of that salty, humid air. Each day, some of it condensed inside. Over months, the accumulated moisture – combined with salt residue – slowly corroded the contacts.

The IP68 rating had never been violated. But the connector wasn’t designed to handle this kind of environmental stress.

Step 3: The Diagnosis – Not a Leak, but a Design Mismatch

We confirmed our diagnosis through a simple test:

1. We took a new sample of the same connector and sealed it with a humidity sensor inside.

2. We placed it in a thermal chamber and cycled it between 10°C and 40°C for 100 cycles.

3. We monitored internal humidity levels.

The results: After just 20 cycles, internal humidity had risen from 40% to over 85%. After 50 cycles, visible condensation had formed on the interior surfaces.

The connector wasn’t defective. The connector wasn’t “not waterproof.” The connector was simply the wrong choice for an application with daily thermal cycling in a high-humidity, salt-spray environment.

Step 4: The Solution – Three Fixes That Worked

We proposed three changes to eliminate the problem:

Fix 1: Vented Connectors

We replaced the standard solid connector with a version featuring a hydrophobic vent membrane (similar to a Gore‑type vent). This membrane allows air and water vapor to escape but blocks liquid water from entering. It equalizes pressure inside the connector, eliminating the “breathing” that was drawing in moist air.

Fix 2: Dielectric Grease

We applied a high-quality dielectric grease to the contacts and the seal interface. This serves two purposes:

• It repels moisture from the contact surfaces

• It lubricates the seal, ensuring proper compression and reducing micro-gaps

Fix 3: Seal Material Upgrade

We upgraded from the standard seal to a silicone-based seal with better resistance to temperature cycling. The original seal was showing signs of compression set – it had flattened slightly over time, creating the microscopic gaps that enabled the breathing effect.

The result: The customer installed the new configuration on one test site. Six months later – zero failures. They’ve now rolled out the solution across all their sites.

What We Learned – And What You Can Learn

When to Consider a Vented or Specialty Connector

Not every application needs a vented connector. But consider upgrading if your application has:

• Daily temperature swings of 15°C or more

• High ambient humidity (coastal, tropical, or indoor with condensation risk)

• Equipment that cycles on and off (generating heat then cooling)

• Previous unexplained failures with no visible water ingress

Final Thought: Sometimes, “Waterproof” Isn’t Enough

The connector in this case study was doing exactly what it was designed to do – keeping liquid water out. But it wasn’t designed for the invisible threat of water vapor and thermal pumping.

A connector that passes IP68 in the lab but fails in the field isn’t necessarily defective. It’s often simply mismatched to the environment.

The best connector isn’t the one with the highest IP rating. It’s the one that’s engineered for your specific combination of temperature, humidity, and exposure.

FAQ – Condensation and Thermal Cycling

Q: How can I tell if my connector is suffering from condensation rather than a leak?
A: Look for fine moisture film or droplets on internal surfaces – not pooled water. Also check for corrosion that seems to start at the contacts rather than at the seal interface.

Q: Can I add a vent to an existing connector?
A: Not easily – venting requires a specialized membrane and housing modification. It’s better to specify a vented connector from the start.

Q: Does dielectric grease really help with condensation?
A: Yes – it creates a barrier on contact surfaces and helps fill microscopic gaps in the seal interface. But it’s not a substitute for proper sealing.

Q: What seal material is best for temperature-cycling environments?
A: Silicone or Viton (FKM). Both maintain flexibility across wide temperature ranges and resist compression set better than NBR.