This week's questions is a follow up to last week's question regarding changing circuit breaker settings while energized.

Here it is:

Have you ever had a breaker trip when changing the setting while energized?
Yes
No
Have not made changes while energized

Stories are always encouraged!

About 20 years ago I had an electronic trip breaker trip when adjusting the setting higher while live. I did not think increasing the setting would be a problem but it turns out there was a logic flaw in the first generation of these breakers (withholding manufacturer's name) and when you go from one setting to another it dropped to zero in between settings. - oops.

Never an issues with modifying relay settings. However there have been times when testing technicians have removed relays where the make before break contacts fail to operate correctly and the breaker trips. Even though draw-out relays are designed for this, most manufactures do not recommend you do it. My experience is that there is a 20%+ chance you will trip the breaker.

I might be jumping ahead a little but but to become a hazard, we need a double fault; a defective breaker that results in an arcing fault during a trip, an obscure relay with a design flaw, and of course to be at the wrong place at the wrong time. I'm sure that there is a chance that this could happen but it is pretty unlikely. It is far more of a nuisance tripping issue and the nuisance tripping issue is more likely to get attention than the very remote double fault risk. I wouldn't rank this one as a hazard.

As to the question, I've run into this same issue with an early model electronic trip unit one time. I'm 99% sure I remember which one it is but it's been close to 10 years since I've seen it.

It is also possible when doing a "download" on SEL relays. An SEL relay download occurs in groups of settings. So for instance it is possible to download general settings that set up multiple trip sets or to enable more trip functions before the settings for those trip functions have actually been enabled, resulting in a nuisance trip if the existing settings are too low.

Also I wouldn't say that the problem is limited to microprocessor relays. I have had one relay where removing the pin for the tap causes it to revert to the lowest rather than the highest tap setting when the tap is changed.

In all of this I have never seen a breaker fail with an arcing fault during a relay setting change. That doesn't mean that it can't happen but the odds of a double fault are pretty high, just that it has not happened to me.