Electrical Troubleshooting Quiz — Addressing Nuisance Tripping

You work for an electrical services firm, and one of the firm’s clients is a small manufacturing plant. One of the things your firm does for them is conduct electrical testing during the weeklong annual shutdown. The plant has opted for the “testing lite” option, due to budget constraints. So much of the work involves visual and thermographic inspections as opposed to a full testing program.

During the last outage, a 600A molded case breaker was identified as probably needing replacement due to some corrosion and discoloration. So, it was pulled and breaker testing confirmed it wasn’t operating correctly.

About a week later, the Plant Engineer called to complain of nuisance tripping and said he wanted the defective breaker replaced. The baseline testing performed on the replacement breaker showed no reason to suspect a bad breaker, but the Plant Engineer was adamant. So, your firm bought a replacement, performed baseline testing, and installed it. Then one of your guys performed the same testing on the breaker that was just replaced. It was fine.

The Plant Engineer called again, wanting to know if “You people can get your act together and stop installing defective breakers.”

The project manager who handles the account with this plant has asked you for a game plan to address this issue. How might you solve it?

Answer to Quiz

You have to solve more than just a technical issue. First, keep in mind this plant doesn’t have a very good attitude toward testing. That alone indicates they are dealing with a load issue that is causing the breaker to do its job and open the circuit. Something that would have been prevented or at least identified with proper maintenance is causing an overload against which the breaker is protecting the supply conductors.

The Plant Engineer is assuming the breaker is the problem instead of asking your firm to identify the problem. What you must do is persuade him to commission your firm to perform the necessary troubleshooting. The odds of a newly installed breaker that was tested before installation going randomly into nuisance tripping mode are remote in the extreme. For two such breakers, you can consider it to be impossible. You can try to explain it from that point of view. Another approach is to refer to the decades of experience in your firm of dealing with similar problems. Or your own experience, as in “I have seen dozens of similar problems, and it has never been the breaker.”

The fact these started with a replacement breaker means the old breaker that was corroded and discolored was not functioning properly. But the new ones have been.

Connect a power analyzer on the load side of the 600A breaker. A recording DMM would likely show you that the connected load was enough to trip the breaker, but it may not be fast enough to capture transients. Since this is already a sensitive issue, you need to step up to the more comprehensive approach that the power analyzer will permit.

Next, make a list of each load served by that breaker. You want the name of the asset, its asset number, its nameplate current (if provided), the current it draws during normal operations, and the max current it draws in 72 hours (a recording DMM should suffice for this last measurement). It is important to tally up these three types of load ratings; you can then tell if the problem is wired in by poor design (e.g., the nameplates show 620A connected to a 600A breaker) or if there is an equipment problem (e.g., 550A of connected load is drawing 620A).

If it’s an equipment problem, try to determine if it’s starting-related or occurs during normal operations. Toward this end, ask the Plant Engineer for the record of the nuisance trips since they began. If these occur with a particular pattern, such as always after a tooling change, that’s a big clue. If there is no record, ask him to start keeping one.

That’s a plan your project manager can present. However, is it a plan the customer is willing to pay for? Your firm can’t get roped into doing free troubleshooting that is made necessary by the customer’s unwillingness to pay for the recommended testing. Your project manager will need to sharply define the scope of the troubleshooting in the proposal. Whoever is assigned the work will have to stay within those lines. For example, if you are tapped for this and you identify that it is a start-up related problem you stop there unless the scope says to drill down to the exact cause. At each step, your firm can sell the next step of troubleshooting or hand that off to the client if the client doesn’t want to pay for it.

A good electrician often wants to walk away having identified and solved the equipment problem. But a much more important problem to solve is, at least in this case, the customer’s poor valuation of proper testing and maintenance of the electrical infrastructure. If this plant engineer can see the amount of downtime and work interruption that could have been avoided, the plant will make more money and so will your firm. Discuss this with your project manager. You want to identify and fix the more costly of the two problems, which is that reluctance to pay for the proper testing and maintenance.