What's A Partially-Tripped Circuit Breaker?

A new panel was installed but one of the rooms had no power even though the circuit breaker switch was "on." I was advised that this may be a "partially-tripped" breaker and told to flip the switch off and then back to "on." It worked! Power restored.
If the breaker switch was pointed to "on," why was the power off. And what is a "partially-tripped" breaker? TIA.
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Circuit breakers can trip two ways. First a human can flip it all the way off. Second, excessive current can flip the breaker part way off (still fully disconnected) so that you know this tripped due to a safety issue.
To reset a breaker that has tripped due to an electrical problem (not due to a human), one must first flip breaker all the way to off, and then flip it all the way back to on.
A partially flipped breaker is a warning to the human who resets it - "Houston, we had a problem".
Marie wrote:

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wrote:

Yes, that's how you reset a tripped breaker: switch it off, then on.

There is no such thing as a "partially-tripped" breaker. When a breaker trips, it trips. Period.
Breakers have *three* positions, not two: on, tripped, and off. The tripped position is midway between on and off. Sometimes, when a breaker trips, the handle doesn't move very far, and the handle is still near the on position, making it appear at first glance that the breaker is still on. Sounds like that's what happened to you.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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Doug Miller wrote:

And if the breaker was truly in the 'on' position, you have a very faulty breaker. Replace it. You can tell a tripped breaker by comparing its position against the ones above/below. It should be distinctly out of position.
Harry K
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