Adjusting trip settings on energized breakers

[polarseltzer]

Recently we had a study done and adjustments were recommended for both arc flash reduction and coordination in the report.
Can adjustments be made to breaker trip settings while energized? Our electrician says yes, he has down it on instantaneous but I am unsure on the other settings recommended like short time delay, etc.

 

[DTR2011]

I would say NO. Unless you know that changing a setting is not going to cause an unexpected operation it is not worth the risk. It also depends on the specific trip unit. I am assuming you are talking about LV breakers, but with (separate) protective relays if it is a 'Tap Plug' or similar, you may risk the chance of open circuiting a CT. If it is a microprocessor based trip unit, this is less likely.

I would not do it myself.

 

[dpc]

If this is a low voltage circuit breaker trip unit, then it's not really advisable. You can query the manufacturer, but I suspect they will advise against it. Things like short time delay settings should not really cause an issue assuming that the unit doesn't pick up while you're making the change. But I don't think it is worth the risk. Just take a short outage. Then you can also TEST the breaker after you make the settings changes.

If it's a separate microprocessor relay, you can probably do it, but there is always some risk of a nuisance trip. I've done a lot of these settings changes will energized - only had a couple of trips.

 

[jraef]

There are what are called "Maintenance Mode" low voltage MCCBs now with electronic trip units that have two adjustable trip settings, one for normal operation, one for lower acr flash energy. The trip settings change by digital input (contact closure) so that you connect a switch, usually keyed, on the front to allow for changing to the arc flash reduction mode WHEN someone is working in front of the equipment, understanding that it eschews coordination with down stream equipment at that time. then when the work is done, the breaker is put back into "normal" mode.

"Will work for (the memory of) salami"

 

[iceworm]

Can adjustments be made to breaker trip settings while energized?

Maybe. I've done it a few times on electronic trip units and have not had a trip (yet).

However, I do cheat and read the IOM first. And, yes, if the manual was not clear, I would call the mfg - although I never have. If the manual is not clear, I highly suspect the mfg rep will be fuzzy as well.

Second, I wouldn't do it on a critical circuit (as defined by the owner - where an unanticipated trip causes hate and discontent).

Third, if it is hotel load, I tend to warn every one in the area of a possible power outage. No use having anyone dangling in the dark.

Why so cautious?

1. It's amazing how often the sun moon and stars line-up.

2. I am neither above or below fat-fingering the buttons.​

ice

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