This week's question is the first of two parts.

Have you ever made circuit breaker protective setting changes while the breaker is energized?
Yes
No

This one always puzzles me. Every manufacturer has a little "lawyer line" some place in the documentation that says that this can be a problem. From my own perspective I can think of 3 potential issues:
1. A fault occurs during a setting change. Frankly this is a "just walking by" situation...it could happen but the likelihood is pretty low.
2. The adjustment causes a nuisance trip.
3. The adjustment causes an undetected failure which later results in a failure to trip.

In terms of the latter two cases there are three possible failure modes which can be applied in either case:
A. The breaker already had a hidden failure. The setting change does not reveal it.
B. The breaker already has a hidden failure. The setting change triggers the pre-existing failure.
C. Human error in making the adjustment creates a hidden failure that did not previously exist.
D. Human error in making the adjustment causes a non-hidden failure (e.g. it trips during the change).

If we do it in conjunction with a breaker PM, then we have some additional failure modes:
E. Removal of the breaker causes a failure.
F. PM of the breaker causes a failure.
G. Re-installation of the breaker causes a failure.

The specific consequences depend on the type of failure. As an example let's consider if the consequence is an arc flash an work backwards. Modes A and D would not cause an arc flash hazard during the setting change although mode D may later be a root cause of an arc flash injury due to an incorrect setting change. With either case the likelihood of an arc flash during insertion of removal of draw-out circuit breakers is about 5 times higher than normal operation of the breaker so modes E, F, and G have a much greater risk than an online change. De-enerizing as would be required with bolted breakers does lower the risk but not much more than that of making the chanee outright. Perhaps the biggest concern overall is the risk of human error causing either a breaker not to trip (hidden failure induced by the change) or the operational issue of causin a nuisance trip. But from a pure safety point of view, the risks are lower than the offline case.

Perhaps the best case is when the trip unit can be removed independent of the breaker. This is especially important with electro-mechanical relays. I've seen many times where a latent defect is revealed by doing a setting change. For instance moving a pin may have an issue with a broken wire or a loose joint that was not visible with the normal practice of simply testing the relay as-is.

This is not an uncommon occurrence on medium and high voltage breaker, particularly when the protective relays are in the control house. I have not done it on low voltage breakers, and am a little more hesitant on medium voltage self contained breakers.

We've adjusted breaker setting with the breaker on, but don't like doing so. To the best of my knowledge manufacturers don't recommend adjusting a trip unit with a breaker energized. However, shutting off a system or breaker can often cause other issues. We have a standard practice when asked to shut off higher amperage breakers. Part of that process is NOT tripping the breaker. Electricians will often press the trip button to trip a large breaker. Tripping a large breaker that's not been off for some time can result in the breaker being difficult or impossible to reset. Here in the southwest, many breakers are exposed to extreme temperatures and it's often years between being shut off. The problem is the high temperatures cause portions of the lubrication to evaporate. When that happens, the trip and reset mechanical portions of the breaker get very hard to operate. We often see older breakers with the handle broken off.

I wanted to follow up with my comments about tripping breakers and resetting them. I mentioned that we often see breakers with the handles broken off. What I think happens is a person has used the trip button on a higher amperage breaker to shut the breaker off. He's finished up whatever work had to be done and now needs to reset the breaker. But because he's released the trip mechanism on a breaker that's not been off for years, the trip won't catch. So this person (understandably) gets excited; I mean the power is off and he'd damn well better get the power on! So he's got to reset this breaker, but the trip release won't catch. So he begins pushing on the handle. He pushes harder and harder until the handle actually breaks off. "Oh *#%!!!" now he's really screwed. You ever do this or see it happen?

A BASF union plant in Georgia insisted on using GE drawout breakers because the handles are plastic (only manufacturer that does this) and broke so much they stocked the parts. It's a 1 hour job and a 4 hour callout on overtime so they loved getting paid for 6 hours of work. They were pretty upset when the GE breakers started getting phased out.