Industrial connections and TPM: how to turn the forgotten electrical point into planned reliability

In TPM, a component without a standard of normality does not generate a tag, and what does not generate a tag does not make it into the plan. The electrical connection is the most common example of this gap. After the first heavy cleaning in autonomous maintenance, the tag board fills up with leaks, missing bolts and perished hoses; a connector almost never appears. Not because it was in good condition, but because nobody defined what a good connection looks like.

TPM (Total Productive Maintenance) requires every component capable of causing a loss to have a standard: what is normal, who checks it, how often, and what to do when something deviates from normal. Connections are found on motors, sensors, luminaires, panels, valves and scales, and they rarely receive this treatment. The argument of this article is that they should, and that much of the work is solved in the design, before inspection.

Why the connection drops off the TPM radar

Three characteristics explain why it is forgotten. The first is that connection failure is usually silent and intermittent: moisture gets in slowly, oxidation progresses over months and the symptom appears as a sensor that fluctuates or a circuit breaker that trips on rainy days. The second is that the connection stays hidden inside boxes, cable trays and junction boxes. The third is that many splices are made never to be opened again, encapsulated in tape, compound or resin.

There is also a structural problem. Connection failures are rarely random in the statistical sense; they are wear-out failures. The rubber of the seal undergoes permanent deformation under compression (compression set): with time and temperature, it loses the ability to recover its shape, and the seal loosens. At the contacts, vibration and thermal cycling produce micromotion and fretting corrosion (fretting); oxidation raises contact resistance and causes localised heating. A wear-out mechanism is exactly what condition-based maintenance knows how to track, provided the point can be seen.

In the material Techno do Brasil presented at Mundo SENAI, described in the series guide, one of the badges on the cover read “Resin-gel free”: sealing with no resin and no gel. From a TPM standpoint, this is the point I consider decisive. A connection that can be opened, inspected and closed again fits into a maintenance plan; an encapsulated splice only allows cutting it out and redoing it.

The introduction to the topic is in Industrial electrical connections and productivity.

The connection within the six big losses

TPM organises the losses of a piece of equipment into six categories. Any of them can have a connection behind it.

The last row often comes as a surprise. Idle equipment cools down, and the air inside the sealed enclosure loses pressure in proportion to the absolute temperature (ΔP/P ≈ ΔT/T). Cooling from 60 °C to 20 °C reduces the internal pressure by about 12%, a suction equivalent to a 1.2 m water column, which draws humid air through any micro-path; at start-up, the condensed moisture is there. The phenomenon is explained in detail in Condensation and water ingress in connections. To measure the size of these losses in availability, OEE and TEEP show where the time goes.

What makes a connection easy to maintain

In TPM, a good component is one that fails rarely and also allows simple inspection, quick repair and error-free replacement. Based on the Techno general catalogue and the presentation, some attributes fit directly into this logic.

Re-inspectable, with no resin or gel

The catalogue describes the TEETUBE® line as free of resin or gel, which makes it possible to open the connection and return to it after long periods of operation. Sealing is provided by rubber elements, not by a material that hardens and seals everything for good.

Plug and socket with locking

The disconnectable series have push-pull, rotary or bayonet locking. For maintenance, this means replacing a motor, a sensor or an instrument by releasing the connector, without dismantling any wiring. Repair time falls, and so does the risk of reversing a connection.

Declared mating cycles

The catalogue tables state, for each series, 100 or 1,000 connection and disconnection cycles. This guides the choice: an instrument that comes out for calibration every month calls for a high-cycle series; a permanent splice does not.

Co-moulded seal and pre-wired versions

The presentation showed the co-moulded seal, in which plastic and rubber are injected together and adhere through a chemical-mechanical bond. Techno summarises the effects in three points: quick installation with few components, fewer installation errors and greater reliability. In DFMEA terms, each loose sealing ring and each assembly step is a failure mode with its own occurrence; co-moulding eliminates one interface and one step, and reduces occurrence by design. It is poka-yoke at the source. The pre-wired versions, with the cable injection-moulded and tested at the factory, take the idea further: less field assembly, less variation.

Materials that age slowly

The service life of a connection depends on the material as much as on the seal. The presentation detailed the tests: body in PA66 with 30% glass fibre, range of −40 °C to +125 °C, ozone ageing (ISO 1431-1), salt spray (EN 60068-2-11), 1,000 hours of UV exposure (EN 60079-0), UL 746C f1 classification for outdoor use and IK08 impact resistance, with a maximum of IK10. For the maintenance planner, each test corresponds to a degradation mechanism that no longer requires intensive monitoring. The distinction matters because the IP rating is a type test: short, under controlled conditions, with the assembly new and correctly fitted. Ozone, UV, salt spray and thermal ageing lie outside it, and they are what define life in service.

Autonomous maintenance: the inspection standard for the connection

In autonomous maintenance, the operator takes on cleaning, inspection and minor adjustments. For the connection to be part of this routine, it needs a visual standard that fits on a card. A starting proposal:

Two precautions make a difference. The operator inspects from the outside; opening a connection, measuring insulation and replacing components is a maintenance task, always with lockout/tagout of energy sources. And the standard only works if the connection is visible: if it lives inside a box closed with screws, the first kaizen may be to bring it outside with a panel connector.

Planned maintenance: criticality, predictive and replacement

Whatever the operator cannot resolve goes up to planned maintenance. Here the work is engineering, and a simple sequence helps organise it:

1. Classify criticality. Connections in safety circuits, main drives and control instruments come first. A connection that stops the whole line cannot be treated the same as the storeroom luminaire.
2. Define condition-based inspection. Visual checks on the routes, insulation resistance measurement on splices exposed to moisture (a gradual drop reveals water before the short circuit) and infrared thermography on power points, where increased contact resistance turns into heat before it turns into failure.
3. Standardise replacement. A few families per function reduce the stock of spare parts and MRO and the risk of using the wrong part at three in the morning.
4. Record with a coded cause. “Electrical fault” teaches nothing. “Water ingress at the splice of motor M-12” does. A well-configured CMMS turns these records into a visible pattern.
5. Use the shutdowns. Replacement of critical connections and re-inspection of buried splices go into the scope of the planned shutdown.

One of the cases in the presentation illustrates item 2 well. At a football pitch with underground lighting, the installer went back to an inspection chamber that fills with water on rainy days, opened the connector four years after installation and reported finding no trace of water at all. It is a single observation, but of a kind that a laboratory test cannot replace: real conditions, a long period, a re-opened seal. And it was only possible because the connection was not encapsulated. This and other examples are collected in Electrical connection cases in harsh environments.

Maintenance prevention starts in the electrical design

TPM has a pillar that many plants leave for later: early equipment management, or maintenance prevention. The idea is that new equipment should already arrive easier to operate and maintain, because the lessons from past failures have been fed back into the design.

It is in this pillar that Techno's proposal proves most consistent. The company presented a three-step method for a correct and durable electrical or signal installation:

1. Analysis of the external environment: humidity, water, chemical agents, pressure, heat, temperature variation and condensation.
2. Selection and harmonisation of the cables: outer diameter, number of poles, cross-section of each pole and the cable's technical specification, such as EPR for damp locations or polyether-based PU, immune to hydrolysis.
3. Elimination of all weak points: circuit floor plan, distances between components, identification and counting of all cable interruptions (straight splice, T, Y, H or multiple branch), changes of conductor size and distances between interruptions.

The third step is a survey of failure modes before the failure exists, and it has a quantitative basis. In a circuit, cable interruptions act as elements in series: R_system = R₁ × R₂ × … × R_n. With illustrative numbers, 20 connections with 99% annual reliability each give 0.99²⁰ ≈ 0.82, or about an 18% chance of at least one failure in the year. There are two levers: reduce the number of interruptions and raise the reliability of each one. Each interruption eliminated is also one less point in the inspection plan. Anyone who works with FMEA will recognise the logic.

In my assessment, this is what makes the approach a differentiator, not the catalogue itself. The connection is treated as a system (environment, cable, interruptions, connection, validation), with interfaces and assembly steps reduced by design, coverage of the failure mode that IP does not cover (condensation, with the xDRY line) and material qualified for the service life, not just for the test. That is maintenance prevention in the strict TPM sense. And the 1-10-100 rule of thumb explains why it pays off: what costs 1 to prevent at the design stage costs 10 to correct during installation and 100 when it fails in operation. The disconnectable connection, in turn, reduces MTTR by design. The specification criteria are detailed in How to choose industrial electrical connectors.

Metrics to track the effect

The effect has to show up in the maintenance numbers. Four metrics are enough to start with:

If the same connection fails again after replacement, do not replace it a third time. Open a root cause analysis and ask why the system allowed the failure: specification, installation, inspection standard or an environment that changed.

TPM applied to connections depends on two conditions: a standard that tells the operator what a normal connection looks like, and a design that allows it to be looked at. Without the first, the point is invisible; without the second, it is inaccessible. To see the company and the portfolio behind the examples in this article, the guide to Techno do Brasil gives the overview, and the link to Lean wastes is covered in Lean and waste in component selection.

Frequently asked questions

Is the electrical connection part of TPM?

Yes, like any component that can cause a loss. In practice, it goes into the inspection standard of autonomous maintenance, the criticality classification of planned maintenance and the design criteria of early equipment management.

What inspection can the operator carry out on a connection?

A visual inspection from the outside: mating and locking, condition of the cable and cable gland, cracks or heat marks on the body, presence of water or oxidation, and legible identification. Opening, measuring and replacing are left to maintenance, under lockout of energy sources.

Why does a resin-free connection help maintenance?

Because it can be opened and re-inspected. A splice encapsulated in resin neither shows its internal condition nor allows the seal to be redone; all that is left is to cut it out and redo it.

How do I know whether the change to the connections has worked?

Compare corrective work orders by cause, MTBF, MTTR and downtime hours from electrical causes before and after, over a period long enough to cover the seasons of the year and the washdown cycles.

What is the first step to include connections in the TPM plan?

Choose a machine with a history of electrical failure, map all its connections and cable interruptions, classify environment and criticality, and create the inspection card for that machine before expanding.

About the author

Vagner Soares

Specialist in Lean Manufacturing and Behavioural Management

More than 20 years in the automotive and metalworking industries (GM and Dana), and a Lean Manufacturing specialist since 2006. SENAI instructor and mentor in the Brasil Mais Produtivo programme, with consulting, training and audits in more than 50 companies, bringing together quality, productivity and people development.

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