Electrical troubleshooting sample question

Use the wiring diagram shown to the questions below:

1) The seal circuit of CR1 has become increasingly intermittent over the last several weeks and now only seals in the relay about 50% of the time on average. What are the possible problems (and root causes if applicable)? 

   A) The most likely causes of an intermittent issue on the sealing function would be; either, a loose connection between TB31 and pin 1 of CR1 or between TB32 and pin 3 of CR1, 

OR

Degrading (increasing resistance) between the N.O. contacts between pin 1 and 3 of CR1 relay. There are many possible causes, including:

• Moisture or other contamination into the relay body causing corrosion or coating of contact surfaces.
• Pitting/damage to contact surfaces from inductive kick (common problem in DC magnetic loads like relay coils) possibly caused due to failure of a surge suppression device such as a reversed diode or MOV or equivalent. This is why it is so important to include Step 6 of the Troubleshooting Procedure "Failure Analysis". Many times, when the surge suppression device fails, the contacts it was protecting will fail numerous times before some savvy technician recognizes the real cause of the problem. This is one of many examples of why a truly strong technician is so valuable on an I&C team. 
• In some cases, the contacts may have simply reached end of life, or there could be other factors at hand such as power problems or excess current. 

Side note - when I grade this troubleshooting exercise in my hands-on Electrical Troubleshooting courses I am looking for the following:  (for this example, assume I have inserted a fault that has degraded relay contacts between pin 1-3 of CR1 - by subjecting them to thousands of inductive kick cycles in my 'shady laboratory'. The tech should:

They should observe that it works each time with PB9 but sometimes fails to seal. This means the coil is good and the start button is working along with the rest of the start circuit from TB33 to TB9 and on to TB6. This should allow them to logically isolate the possible faulty sections to everything between TB31 and TB32, which includes interconnecting wire & applicable TB's, CR1-1a contacts, or the relay terminal base. 

They should now begin confirming the problem is where they suspect. Lots of options on how to flow through this maze, but in short, I like to see something like this; While not pushing PB9, push the manual relay activation button (which should close CR1-1a contacts) and measure voltage between each of the following points - if they see non-zero voltage, that's the open portion of circuit:

TB31 to pin 1 of CR1

Pin 1 to pin 3 of CR1

TB32 to pin 3 of CR1

Based on damaged contacts of CR1-1a, they would see a voltage between pin 1-3. Depending on the amount of resistance of the contacts in comparison to the relay coil resistance, they may see a wide range of voltages, but suffice it to say they should see something fairly substantial many of the times that they operate the relay actuator.

Note - in real contact failures these intermittent problems can be hard to troubleshoot because you basically have to test enough to get some statistical data. If you only test it one time and the contacts happen to line up with good points on both ends, it will likely read 0.0v - but remember, it was an intermittent problem... so factor that into the testing.

Once they have identified the faulty section to be between pin 1-3 of CR1, they might pull the relay from socket/base to determine if the problem is truly the contacts or possibly a problem in the terminals or socket pins. They may ask to swap out the relay and in real world scenarios this is ok, but in training I typically tell them the relay costs $500 just to force them to truly troubleshoot it all the way to fault proof with resistance check of contacts while operating the manual relay activation button. 

Then of course, I want them to hypothesize on possible causes, which we covered above. I sometimes will have them use a relay with a cracked housing that ironically has a twin cracked relay that is faulted so they don't suspect it. The likely cause on this one is environmental contamination - Teflon powder for instance. 

These are just hypothetical scenarios designed to make people think and get them to apply good troubleshooting habits and practices. The biggest weakness I see in troubleshooting is that people rush in and don't think about how to logically isolate and prove where the problem is. So, I emphasize that heavily in the training. 

In fact, to encourage the focus on logic, I have them informally keep score of each troubleshooting scenario where each voltage/resistance check counts as a shot and they shoot for low score like in golf (I even give them an approximate par shot value for each fault to help push them to focus more on logic than speed. Swapping parts without sound reasoning and/or if they are wrong, is like a foul.

By the time students have troubleshot 6-10 problems of increasing complexity they typically have some new (good) habits and better approaches in troubleshooting and I hear from customers that these improved logical approaches extend well beyond purely electrical problems.  

Fun Fact - I helped one of my customers develop a system to test practical troubleshooting skills of incoming electricians using a training simulator much like the one I still use for these sample problems with several levels of electrical faults. It made a huge difference in the screening as well as helping identify gaps and upskilling their existing workforce. It was interesting to observe folks who claimed to be seasoned experts struggle to identify basic faults. Many times it became quite obvious that the candidates didn't really understand basic electrical concepts at all.  

Side note - I often suggest to my customers to make use of some of the online simulations for troubleshooting as well, to help maintain skills - but I recommend learning with real hands-on equipment initially to help connect the concepts to what they'll be doing in the field. Once the theory to field associations are solid in their minds, online and PC based troubleshooting simulations are a fantastic aid in skills retention. 

If you are thinking, man that sounds like a fun class - you are correct! Our new ELTS course is one of the most enjoyable classes I've personally taught in my 40 years because I see a ton of progress in the students and also because solving these types of problems 'what we do' as techies. Students always rave about how much they enjoyed it and how much they learned, and managers tell me it creates a noticeable impact on uptime and MTTR and a reduction in improperly swapped parts and mistakes.

Reach out today if you'd like us to deliver a custom version of this course at your facility or see our upcoming schedule to register for a public offering of our 3-day Basic Electricity & Electrical Troubleshooting course. 

PS - One additional point on this hypothetical exercise: I claim that the contacts were destroyed by inductive kick in my explanation, but in reality, the NO start contacts would not experience inductive kick typically because the contacts are engaged by the time you let go of the start button. The stop button would absorb some inductive kick when it is pushed - but not the start button. I had honestly missed that until pointed out to my by a deep-thinking super tech (kudo's Gary Lucas!). I love it when I learn new things or stretch my mind, and posting these blogs seems to keep me learning due to ideas and input from high level people like Mr Gary Lucas - usually a bit humbling, which is also probably good for me.