What Happens When PLCs Are Stored Incorrectly
The assumption is almost universal in industry: PLCs are rugged hardware. They’re built to run in harsh plants, tolerate electrical noise, and survive decades in panel boards. That reputation for toughness, however, refers to PLCs in operation, correctly installed, properly ventilated, and within spec. A PLC sitting in a warehouse is a different story entirely.
The Damage Nobody Sees Coming
Every year, industrial facilities commission new equipment, pull PLCs from storage, and encounter the same bewildering problem: a unit that tested fine at the supplier fails on first startup. Or worse, it starts up, runs for a short period under load, and then fails unpredictably in the weeks that follow.
The root cause, in a significant number of these cases, is not a manufacturing defect. It’s what happened in the warehouse. Improper storage degrades precision electronics silently and progressively, leaving no visible evidence and no obvious fault code, just a component that’s already past its prime before it ever enters service.
A PLC doesn’t need to be running to be damaged. The warehouse environment can begin degrading sensitive electronics long before the unit is ever switched on.
The Four Silent Threats in Storage
1. Humidity & Condensation
Moisture infiltrates circuit boards and corrodes copper traces, component leads, and connector pins, damage that may not manifest until the board heats up under load. A single condensation event can bridge conductors or initiate corrosion that progresses invisibly for months.
2. Electrostatic Discharge
The human body can carry thousands of volts of static charge. A single unprotected handling event can punch through gate oxides in CMOS components, causing immediate failure or, more dangerously, latent damage that weakens the device without killing it outright.
3. Temperature Extremes
Thermal cycling, repeated heating and cooling across a wide range, stresses solder joints, expands and contracts component housings, and can crack PCB substrates. A PLC stored in an uncontrolled outdoor container or near a roof in summer is accumulating stress with every day that passes.
4. Dust & Contamination
Conductive dust particles settling on open boards or inside unsealed enclosures create resistive or capacitive paths between conductors. Fine metallic dust, common in fabrication environments, is particularly destructive, creating short-circuit paths that are invisible to the naked eye.
Latent damage is the most dangerous kind
A PLC with ESD damage or corrosion-weakened solder joints may start up and pass initial testing, only to fail weeks later under thermal load or vibration. By that point, the storage origin of the failure is rarely suspected, and the unit is often replaced rather than root caused.
How to Store PLCs Correctly
None of the requirements for proper PLC storage are exotic or expensive. They’re basic environmental disciplines that protect a significant capital investment. The problem isn’t a lack of available solutions, it’s that the risk is invisible until it isn’t.
Essential Storage Factors:
- Controlled Temperature: Store between 0°C and 40°C, away from heat sources, roof exposure, and direct sunlight. Avoid spaces with large daily temperature swings.
- Dry Conditions: Maintain relative humidity below 60%. Use desiccant packs inside packaging for long-term storage. Never store on concrete floors where moisture can wick upward.
- Anti-Static Protection: Keep units in original anti-static bags or ESD-rated packaging. Handle with grounded wrist straps. Never place on or near synthetic surfaces or foam that hasn’t been ESD-rated.
- Sealed Packaging: Original manufacturer packaging is designed to protect against all of the above threats. Once opened, reseal in clean polyethylene bags with desiccant before returning to storage.
For high-value or long-term storage, spares held for critical systems, consider a dedicated electronics storage cabinet with humidity control. The cost of a storage cabinet is trivial compared to the cost of a failed PLC on a production-critical line.
The Broader Principle: Failure Doesn’t Wait for Commissioning
The conventional model of industrial reliability focuses on operating conditions, temperature in service, vibration loads, duty cycles. These matter enormously. But the clock starts running the moment equipment leaves the manufacturer, and every phase of its journey before commissioning is an opportunity for degradation.
Transport shocks, improper stacking, uncontrolled storage environments, unprotected handling, each one places stress on precision electronics that were designed to operate within specific bounds. When those bounds are violated in the warehouse, the consequences show up on the production floor.
Treating PLCs and other sensitive control hardware with the same rigour in storage as in service isn’t overcautious. It’s the minimum standard for protecting capital equipment and ensuring that what gets commissioned is what was purchased: a fully capable, uncompromised unit.
Industrial Equipment Can Fail
Before It’s Ever Switched On.
The warehouse is not a neutral environment. Treat your control hardware accordingly and protect your commissioning day from the damage that started months before it.