You’re the electrical supervisor in the maintenance department with seven electricians reporting to you. But maintaining electrical infrastructure is clearly outside their ability range. This recently came home to roost in the form of nuisance tripping of a feeder breaker several times a day.
You convinced the plant manager to let you hire a local electrical services firm to perform the necessary testing and troubleshooting. You also noted it’s an adjustable breaker, and you sent a request to the firm that did the coordination study to send you the documentation. To avoid a trip until the facts can be determined, you locked out four machines that can afford to be down for a few days.
The next morning, the plant manager told you to cancel the contractors because he came in the previous night and fixed the problem by adjusting the breaker to max. What troubleshooting steps must be done, and how do you convince the plant manager to let you proceed?
Answer to Quiz. Explain to the plant manager that if there’s a fault on that feeder, the upstream breaker will likely trip in the event of a branch circuit or feeder fault, resulting in the whole plant going dark.
Then point out that Art. 240 of the NEC has complex requirements for adjustable breakers. The plant’s insurer requires the plant to follow the NEC. There’s also an OSHA problem with an unqualified person working on energized electrical equipment. It’s not as simple as turning the volume knob on your radio. Point out that NFPA 70E has complex requirements for this work, and adhering to them is even more complex because the condition of the breaker is unknown. Therefore, that equipment must be considered unsafe, which means additional safety procedures such as a hot work permit.
Tell the plant manager you need an electrical services firm to come out right away and adjust the breaker to the correct setting. They also need to connect a portable power analyzer to determine what that breaker is seeing in terms of current and power quality. You don’t have the expertise in house to do this safely or correctly.
If there’s a record of the previous setting, have the electrical services firm return the breaker to that setting. If there’s not a record, get that coordination study documentation expedited. Call them, and stay on the line until you get the breaker setting information.
The troubleshooting must involve several things, starting with a determination as to whether the breaker is properly set. If not, properly setting it should stop the nuisance tripping. If it the setting is not the problem, the cause of the nuisance trip must be determined. It is rarely the case that a breaker fails by nuisance tripping. The normal failure mode is it doesn’t open, and that’s because inadequate maintenance results in things like dirty, stuck mechanisms.
Stress to the plant manager that an electrical services firm will already have a standard procedure for efficiently, safely, and positively identifying the cause, and they will have both the test equipment and the qualified personnel to execute that procedure. Your plant doesn’t have any of those things, so bringing in the firm is the most cost effective way to restore reliability to that feeder circuit.