Electrical Troubleshooting Quiz — August 16, 2022

A few months ago, the plant hired its first-ever electrical maintenance engineer — you. The plant engineer told you during the interview that after 11 months, corporate would evaluate the economic value of the job to determine whether to keep it or eliminate it at the one-year mark. She noted that, given your salary, something big would be needed. You agreed to this, and now that you’re on the job it’s time to find “something big.”

This plant has a slightly higher rate of cable failure compared to that of the other nine plants in the division. Initially, the plant engineer had not thought something big would be there. However, Bob, a senior electrician, said the numbers don’t tell the whole story. He said he was sure some cables have been replaced two or three times in the past decade.

The plant engineer plotted all the past 15 years of cable replacements on a spreadsheet. Sure enough, there’s a frequent flyer club. And it’s not just a few cables. Could these replacements be unnecessary, made due to testing anomalies or misinterpretation of the test data? Or were they necessary due to damage that needs to be identified and corrected?

Considering the high cost in lost revenue these cable replacements require, solving this puzzle would more than justify your salary. How might you approach this?

A systematic approach

For seemingly random cable failures, you want to look for systemic issues — those that affect the entire distribution system. However, in this case, you need to focus on the specific cables that have been replaced more than once. You will need to explore five areas: testing, test results analysis, cable selection, replacement installation method, and application-related damage.

1. Testing. Who is doing the testing, what tests are they doing, and are they doing those per the relevant industry standards? Which test equipment was used, and what is its calibration history? A common error with cable testing is an unqualified person (general electrician, not someone specifically trained and certified in this kind of testing) performs a single test via the “wing it” method a single time on a given cable using an instrument on which calibration history is not kept. Based on the results of that single test, the cable passes or fails.

2. Test results analysis. How you interpret the test results determines whether they are useful or not. Insulation resistance testing of cables, for example, is normally useless unless trended over time. For this test, you need to take a baseline reading shortly after installation and then perform testing at the recommended intervals thereafter. A single reading that “seems low” might mean nothing. After you trend a few and see a fairly flat line on a graph, you know that cable is OK. When that line does a hockey stick on you, then you know the cable needs to be scheduled for replacement.

3. Cable selection. Were the failed cables incorrect for the application? Overload is a common cause of conductor overheating; perhaps the ampacity is too low for the application. To address this, use the applicable ampacity table in Art. 310 and apply the ambient temperature correction factors [310.15(B)] and adjustment factors [310.15(C)]. If these were misapplied or not applied previously, you will arrive at a cable ampacity greater than that of the existing cable. And you may have found your smoking gun.

4. Replacement installation method. Incorrect methods of replacing cables can damage them at the outset. Exceeding the bend radius, stepping on cables, and using too much pulling tension are the most common errors. In this particular instance, installation error is the most likely problem. To identify and eliminate the problem, you could make videos of the next cable replacement, if it’s done in-house.

But you have less than a year to solve this. Instead, you will need to meet with those who have performed cable replacements and ask them if they think these or other such practices have been used. If so, make a note of it. Conduct a training session with an open discussion on how best to protect cables during installation.

If this work is outsourced rather than done in-house, bring the issues up with the contractor and let them know you will have one of your people watching for these specific issues and any potentially damaged cables will be replaced at the contractor’s expense (put it in writing, too).

5. Application-related damage. The most common problem here is transient voltage damage. The most common cause of that is across-the-line motor starting. A soft starter is often a good solution.

It’s generally a good idea to quantify your accomplishments in terms of revenue saved. Having those numbers on record is helpful in getting a pay raise or finding a new job. In this particular case, keeping this job depends on the math.

So, for each problem solved, get the revenue numbers from someone in production. For example, a cable that has been replaced three times has cost X hours of downtime on Y machine at Z dollars per hour of downtime. You fixed that for a total of however many dollars it works out to. For each machine, someone in corporate has the profit margin for each dollar of revenue. The total profit you save has to exceed your salary for you to keep this job.