Voices: Real Answers

Any Termination Data on Field Connectors?

We Have Customers With Varying Preferences for the Method of Terminating Field Connections Outside the Panel. We Even Have Our Own Internal Disagreements. We Wanted to Simplify. See What Vendors Said:

We have customers with varying preferences for the method of terminating field connections outside the panel. We even have our own internal disagreements. We'd like to simplify, and we wonder if anybody, whether it's from vendors or independent test centers, etc., has compiled meaningful data, meaning some mean time between failure (MTBF) comparisons about termination failures, which include M8/M12 as well as screw, spring and IDC. It would be helpful to argue a preference based on data rather than mostly subjective or anecdotal viewpoints.

—from June'14 Control Design


Sooner or Later

I haven't compiled any meaningful data, but I would express reservations about the usefulness of MTBF calculations with connectors. I guess you meant mean time to failure (MTTF), as connectors are generally replaced rather than repaired. MTBF is more appropriate for electronic and electromechanical devices where there is some chemical or fatigue based wear-out phenomena. Connector life (or lack thereof) is generally determined by the initial installation, and after that by subsequent insults from mechanical or environmental conditions.

Wear-out phenomena reduce life deterministically according to the Arrhenius relation or similar. For example, insulation in most connectors contains antioxidants, with typically enough antioxidant to get to 20 to 30 years at maximum operating temperature (say 90 ºC), then it goes chalky and brittle. The lifetime doubles for every 10 ºC decrease in temperature. The temperature increases with (square of) current, and typically a pin-socket connector is matched fairly well to the wire gauge, so a 1.6-mm pin might be used on a 1.5-mm2 (or 16 gauge) wire and be “rated” at 16 A. So if you run at 10 A, it should last four times longer (= 100 years), but overload to 20 A, and it will last only 4.5 months.

The point here is that most field wiring has a large safety margin, so it will fail because of something other than old age. My experience is that non-overloaded connectors will last forever until they get wet or until bumped.

My personal experience with field connections is that the M12 connector, when fitted to the rear end of a proximity switch is incredibly unreliable (i.e., about six failures in 80 connectors in three years). The proximity switches are mounted in awkward places inside machinery and usually need to be adjusted by non-instrument-technician workers. The right-angle connector especially is used as a handle to stop the prox switch rotating when the stop nuts are tightened, and usually cracks internally or damages the prox, but it might take weeks before it starts failing intermittently.

The other big killer for connectors is lack of strain relief, and this can be made worse by poor choice of wire (e.g., 26-gauge wire with 600-V insulation is all sheath and no wire).

Finally, any pin-socket connectors that might get wet (i.e., not mounted in the computer room) should have silicone grease applied to the contacts.

Another problem connector is the rectangular one fitted to solenoid valves. Some of these fall apart in months (the ones with clear plastic, so the LED is visible, suffer environmental stress, cracking due to solvents in the oil/coolant/degreaser), and they're usually held on with a really flimsy screw.

Bob Turner,
Salbay Engineering Pty

Also Read: Note to Manufacturing Facilities: It's All About Ethernet

Dial M for Good Connections

I recommend fast connections such as plugs (M18/12/8, etc.) with molded ends. Our wiring problems are close to 0%. The additional material costs compared to the labor and troubleshooting is minimal. Most of the time the job has to be done during shutdowns or weekends. Time is money.

Spring connection (cage clamp) should be used because they never get loose, even from high vibrations. Stay away from putting wire furls on. It doesn't make the connection better and is unnecessary. We use, if the customer allows us, only cage clamp terminals, such as those from Wago, Harting Plugs, Phoenix Contact, even with relays, power contactors, motor controllers, power supplies, etc.

If the customer understands this, it's not necessary any more to tie up all connections. When someone doesn't understand the advantage of those connections, then troubleshooting must be fun for him. I don't know one case in our company when we  ever had a problem with the cage-clamp technique.

Franz Stranninger,
SAR Automation

Same Here

We also go with over-molded connectors for connections outside the panel or for connecting multiple panels together. It simplifies wiring and, other than a rare bad cable, it's pretty much trouble-free.

Mark Will,
automated systems engineer
Labeling Systems

It's Technique, Not Type

I look forward to seeing empirical evidence. I have heard a lot of arguments from suppliers, consultants and end users. My experience is that the terminations that fail are the ones that are not correctly installed (i.e., screws not tightened, crimps not crimped properly, etc.).

Michael McKay,
principal engineer,
Pesce Pty

Cage Clamp for Me

I find cage-clamp style terminals to be the best. Much faster wiring and no loose screws. IDC is great too, but the big problem is the wiring needs to be within specification. Also the same wire can only be connected/disconnected a couple of times before the knife damages the core. Old fashion screw terminals: I see absolutely no reason at all to even consider using them. I think it will be hard to find some sort of statistics on this. If you look at the data sheets of the Phoenix Contact Clipline series, you will find test results of the various types of clamps.

Patrick Stave,
Nordlaks Produkter

Ask the Right Companies

The companies that could answer this are those that fabricate modules or equipment installed off-shore, vibrate or move, and/or are in hazardous areas. The equipment failures due to improper terminations probably are some of their biggest issues.

Alejandro Varga Meder,
project management,
Devco USA,

Spring for Me

I prefer spring terminal blocks over screw connections. Not only are connections faster, but you don't have to worry that the screws are tight. I don't use IDC terminals since wiring never seems to stay “carved in stone,” and they aren't faster unless in high-volume assembly. I always use DIN crimp ferrules on the ends of stranded wire. Most automation wiring is with individual wires in terminal blocks. At www.plctalk.org there's a 12-page thread over 10 years with photos of member's automation cabinets.

A former co-worker worked at a local Siemens rail-car plant and related that he performed extensive testing to qualify terminations for that continuous vibration environment. I recall he said they hadn't accepted spring terminals when he left. The robotics industry similarly spends much time qualifying both connectors and flexible cables. In general automation, wiring is usually sessile, so attributes like corrosion resistance are of more concern. Aerospace is another high-vibration environment. Amphenol circular connectors have long been used there. I think multi-turn collars were first, then bayonet lock, and today a click-lock type seems most common. They can be very expensive.

William Grissom,
engineering specialist,

More From This Voice


Any Termination Data on Field Connectors?

We Have Customers With Varying Preferences for the Method of Terminating Field Connections Outside the Panel. We Even Have Our Own Internal Disagreements. We Wanted to Simplify. See What Vendors Said:


Best DAQ Approach For Machine Controls?

Programmable Automation Controller (PAC) and Data Acquistion (DAQ) Systems Each Offer Unique Avantages in Terms of Information Access and in Granularity


What Are Machine Builders' Wireless Options?

Technology Can Deliver Low-Power Wireless Sensing, But There Are Challenges Such as Range, Rate, Power and Encryption to Consider


Is BYOD Inevitable in the Manufacturing Space?

Is it Inevitable that an RFQ Will Include Tablet or Smartphone Wireless HMI Requirements Some Day?


Experts Weigh in on Best Practices for Control Panel Housings

Design Uncertainties Can Arise From the Increasing Number of Devices in Control Panels Even When Regulations Are Followed to a Tee. Experts Discuss Solutions


How Do We Tone Down Machine Device Chatter?

Are There Standard or Standard-Based Approaches to Filter Networked Hardware and Components Nuisances?


Turn to Pneumatics or Direct-Drive Linear?

Which Offers the Best Bang for the Buck: A Direct Pneumatic Solution or an Integrated Linear Motor Package


Time to Slip Away From Slip Rings?

What Should Our Reader Know About Adding Wireless to Their Rotating Segments of Equipment in Tough, Noisy Environments?


Worry About End of XP Support?

With Microsoft to Stop the Support of Windows XP, What About OS Updates?


Time to Move to Digital Panel Meters?

Experts Share Experiences With Making the Move From Analog to Digital Panel Meters


Do We Future-Guard Machine Designs?

Will Designing Redundant Switches Up Front Forgo Future Problems, Liabilities and Added Costs?


Time for Electronic Circuit Protection?

Continuous Identification and Troubleshooting of Blown Circuits Cause Too Many Headaches for Our Reader


Is an Imaging Sensor Sensible?

How Will Precision and Accuracy Compare to Using a Presence Sensor?


Perplexed by Control Panel Builds

Should Our Reader Bring Its Building Jobs Back In-House or Do Custom One-Off Builds? Our Experts Give Their Advice


Should Machine-to-Machine Scare Us?

Will Implementing Device-Level Networks and Ethernet in Machines Help Your Customers?


Is Wireless the Right Solution?

What Are Readers' Experiences With Machine-Mount Wireless Controllers and I/O?


HMI: Form vs. Function?

Are Industrial Screens Beginning to Look More Like Smartphones?


Regen Drives Take the Heat, but Can They Turn Down the Cost?

What Happened to Pricing for VFDs and What's the ROI Particularly for Regenerative Drive Units?


Learning IEC 61131-3 Programming Languages

System Integrator Asks Our Readers About Receiving Education on Object-Based Programming


Picking a Wireless Standard

Is There Currently a Leading Standard for Connecting Distributed I/O and Sensors That's a Safe Pick for the Future?