you can put the din rail in any enclosure you want.
the din rail screws to the enclosure or subpanel and the fuse blocks snap onto the rail. here is a back view. of something mounted on din rail. din rail is also available with premade slots so you can put the mounting screws wherever it is convenient.
it is called din rail because it is a DIN standard rail. there are all kinds of neat things you can mount on the rails like terminals, small circuit breakers, modules, etc.
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You might also consider some miniature circuit breakers if your AIC requirements are met. They also mount on a DIN rail. These are ABB but a lot of other manufacturers sell them as well.
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