I think this video is a well-produced and informative video that is worth watching for viewers who want to learn about circuit breakers. Here are some key points mentioned in the video: A circuit breaker is a device designed to interrupt a current in an electrical circuit either automatically or manually under abnormal conditions such as overload or fault. Circuit breakers are used for feeder and branch circuit protection and are designed to provide overcurrent protection for overload and short circuit conditions. There are many types and sizes of circuit breakers used in electrical power systems from residential to large industrial and utility systems. If you are interested in learning more about circuit breakers, I recommend watching this video.
While on the subject of miniature circuit breakers, specifically 3 phase breakers, there is an obsolete type, that was actually banned by the NEC in 1978, and it is called a delta breaker, used with high leg delta systems, this oddball breakers plugs onto the 2 bus bars in a residential panel, and has an additional lug for the third phase, the high leg, which typically came directly from the meter base and is usually unfused, and was used when there was only one three phase load in the building, in a residential panel this was mostly used in the 1950s and '60s,for central air conditioning, some of the 5 ton condensers at the time were not available in single phase, and in some parts of the country, notably the Phoenix area, the POCO would install two transformers creating an open high leg delta, to a larger home, just for the new fangled air conditioners post WWII. Delta circuit breakers occasionally pop up on eBay and other sites, and command a hefty price tag, since they are either NOS, or refurbished, pulled out of a pre-1978 install and are therefore almost impossible to find. I think you are still allowed to use one for a replacement in an existing installation, but you might be better off installing a new three phase panel.
Watch the Eaton video on High Resistance Grounded Wye systems and Ungrounded Delta Systems. That video led to me finally finding the reason for wye (primary)/delta(secondary) transformers. As you might already know it’s not an often used connection method for transformers of any kind. These Eaton videos are excellent for filling in the gaps between electrical theory and practical implementation thereof. They rarely make an error in any presentation.
