Likely yes there is some mechanical gearing or at least a reduction gearbox, but that's not the reason for the name. One meaning of 'Gear' is broadly equivalent to 'equipment'. Why they chose 'gear' I just don't know - it's a choice made many years ago - but it does roll off the tongue fairly easily.
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My understanding is - it definitely built with some gears, e.g. spring charging components for energy storage to close or open the breaker without electric power. Some have grounding switch and interlocking mechanism.
Use of the word "gear" is not limited to mechanical gear. Even personal protective items like helmets, pads, gloves etc. are called sports protective "gear". It is in the similar vain.
If the Brits would have gotten there first it would have been called switchkit. Maybe it is because one of their early electrical pioneers was a yankee; Charlie Brush from Cleveland.
Metal-clad: each individual breaker cell is encased (clad) in metal, then the cell itself is inside of another metal enclosure. Individual cells can be disconnected from the bus for safety or completely removed for servicing without affecting the rest of the line-up. So if you need to do maintenance or repairs on a unit cell, the rest of the plant can keep running. If a failure occurs in a cell, it provides a significantly reduced risk of collateral damage to adjacent equipment. Stackable cells and rear cable connections reduces the linear space requirements, but the rear connected bus structure requires a lot of depth. So Metal Clad is the choice for highest availability, but bears the highest capital cost.
Metal Enclosed: (as opposed to what, wood?) there is only one switching device in each structure section. There is no removable cell, so if maintenance or repairs need to be done to a unit, the entire line-up must be shut down because of the risk to exposed common bus bars. This means they are not really suitable for critical equipment that must be kept running while other units are being serviced. Faults are still isolated, but damaged units mean shutting down the entire line-up to replace or repair them. With only one device per section, a lot of switching devices takes up a lot of linear (wall) space. Initial capital costs are however lower.
There are twists and exceptions to these generalities and new designs seem to be blurring the lines but that is the gist of it.
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