Electrical Troubleshooting Quiz — July 19, 2022


You work for an industrial services firm as a senior electrician. ABC Widgets Inc., has a manufacturing plant in town and your firm has always wanted to establish an electrical maintenance contract with the company since it doesn’t have any electricians in its maintenance department. Management always had some reason or another to say no.

But the plant called about a transformer problem and your boss sent you there to investigate. You met with a maintenance mechanic who took you out in the plant to a 75KVA dry-type, pad-mounted transformer. He told you it made a loud hum and put out a lot of heat. However, it wasn’t doing either of those things while you were standing there, so you asked him when this occurred. He said he didn’t personally notice it, but someone reported it the other day.

How can you get to the bottom of this, and do so in a way that shows the value your firm can bring?

Ask questions

Start by contacting the person who phoned your company and see if you can get more information. Who reported the problem? Can you interview that person? On what day did the incident occur, and at about what time? Was anything unusual going on in the plant at that time? Has anything similar to this been reported before? What was the weather that day (eg, any lightning)? Ask if there was a power interruption, lights flickering, or a breaker needing resetting that day.

Also ask if anyone has ever stacked boxes or parts next to that transformer. Might they have done so on that day? If you get an affirmative here, you should consider it a contributing cause rather than the cause— until you rule out other potential causes. If any of those items are flammable, you have an important issue to raise.

Basic checks

Next, perform some basic checks of the transformer and specifically identify anything that is a maintenance issue:

  • Inspect the transformer case. If you could almost grow tomatoes on the top, you have an important issue to raise. The same goes for such things as corrosion or a severe dent.
  • Look for signs of water damage (eg, a trail of precipitate down the side or water stains on the pad or floor) and rodent presence (black objects almost the size of peppercorns indicate mice).
  • Inspect the associated bonding system for completeness and mechanical integrity. A problem here could explain the anomaly, due to circulating currents.
  • Because this is a separately derived source, it must be grounded per Article 250, Part V.
  • Take as much power quality data as your power quality analyzer will permit. If the transformer isn’t misbehaving and there’s nothing such as high harmonics or waveform distortion, you can use these as baseline data should further troubleshooting be needed.
  • Take current readings to determine whether one phase is more heavily loaded. This can happen, for example, if only one phase was used to power a lighting panel.
  • Measure the temperature at the vent; As with some other data, this will likely be only a baseline measurement.

Evaluate the environment

Then evaluate the transformer environment:

  • Determine how heavily loaded the transformer is. If the transformer is already loaded to the gills, an additional load (that is not normally running) can push it past what it is designed to handle.
  • Identify all motors that start across the line, noting the size of each one. Do these all start at the same time, such as the beginning of a shift? Could the combined inrush heat up the transformer in question?
  • Identify any high harmonic loads of sufficient quantity or size to be a potential problem.
  • Note whether the transformer has sufficient clearance and whether the vent is obstructed in any way.

Then look for some Code violations. This is for persuasion purposes. The plant no doubt has plenty of unused enclosure openings. Pick an area and them, so you can say something like, “I found 23 violations of NEC 110.12(A) in the vicinity of this transformer. Each of these is a personnel hazard.”

Keep in mind that you are tasked with more than solving a technical problem. You also must solve a misconception problem, namely that electrical infrastructure takes care of itself until something happens, in which case it doesn’t. If the cause is a phase balance issue, it won’t help you sell them on the importance of electrical maintenance. So while you are in there, you need to document electrical maintenance deficiencies and then discuss the value of eliminating those deficiencies.

You aren’t going to get them to spring for a full-blown electrical maintenance program complete with annual feeder cable testing. Not just yet, anyhow. You must start from where they are and over time move them to where they need to be. The trouble call gave you one foot in the door. Use this visit to get the other foot in the door. Walk gently from there.

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