Electrical Troubleshooting Quiz — July 1, 2025

A local plant hired your electrical services firm. You run a crew of four journeyman electricians and two helpers there on a regular basis. Your crew supplements their work, mainly because your skill level is higher than what the in-house maintenance has. Any time there’s a sticky problem, they kick it over to you.

A 400A molded case adjustable circuit breaker started nuisance tripping. One of the maintenance people solved the tripping problem by adjusting the breaker. But he did not take As Found data and had no technical reference as to what the setting should be. He just turned each setting to what he thought was “all the way up.” The maintenance manager is worried that there is an actual problem the breaker won’t protect against, but he also doesn’t want to experiment with the settings to “figure out where the dial should be.”

How should you solve this problem?

Answer to Quiz

Because there was a tripping problem that may or may not be legitimate, and there seems to be confusion about this breaker, you first need to find out how much current the load is drawing and whether the conductors have the ampacity for it. To do that, connect a portable power analyzer that you can leave in place to take some history. If you don’t have one readily available, then for now attach a current clamp with high recording. Ensure you can put the instrument behind protection; that means inside the enclosure with the door properly closed. If that is not possible, then you will need to red rope the area at the limited approach boundary [NFPA 70E 130.4(F)].

If the load exceeds the conductor ampacity, start removing loads to correct that problem. You will need to ask production about this and ensure they hang their lock and tag on the relevant disconnecting device(s). Since this nuisance tripping problem recently started, it is likely that just another recently added load or two is the problem. For example, a couple of operators brought in personal space heaters. State your findings to the appropriate authority (e.g., the production superintendant) and discuss the available remedies. Don’t confront operators about their space heaters, ask production management to address that problem for you.

With a nuisance trip, you should compare the actual load (which you just determined) to the rated load (look for a big difference, for example a 20A motor is drawing 30A) and also to the rating of the breaker. Also look for things like phase imbalance or low power factor, as these can drive actual load higher than rated load.

Determine if the breaker as rated (excluding any adjustments):

• Is correctly sized for the conductors. If it is oversized for the ampacity, it will need to be replaced with a correctly-sized breaker.
• Can handle both the rated load and the measured load If it’s correctly sized for the conductors but cannot handle either the rated or actual load, some load must be removed.

Whether the breaker is replaced or not, it must be tested as part of the troubleshooting process. If it operates properly, then the nuisance tripping cause does not include any defect in the breaker.

Your next step is to determine the correct settings for that breaker (or its replacement). Locate the installation record, the information should be there. If it’s not, then you should be able to figure this out yourself after you characterize the loads. For example, if this breaker supplies a big motor then you would want to increase the time delay to allow for the inrush current of that motor. Record each setting and your justification for it.

Discuss your findings with the production superintendant or other senior operator, then ask when you can adjust the breaker to these new settings. It would be wise to start them all at “open throttle” and then adjust them downward one at a time. This will allow you to identify an error, if you made one.

Now with this problem fixed, tell your client that the As Found settings for all adjustable breakers need to be entered into the CMMS. If you have access to the CMMS, perhaps a member of your crew can take care of this task.

You’ve also identified a training deficiency that you should discuss with your client. Recording the As Found condition of any equipment, including settings, is required before changing anything. It is important that you push this issue, because in-house people could come behind your people and change things then blame your people for whatever the consequences are.