I have a 100 amp main panel and need to install a 60 amp breaker to run a plasma cutter. The main panel is full and there is no room to add any more breakers so should I try and make room in the main panel by doubling up some smaller breakers or just run a subpanel for a 60 amp breaker. The wire from the plasma cutter is already connected into it's own panel with 2 pole breakers and a shut off on the box. I need to now run the wire exiting that panel into the main panel with a 60 amp breaker.
Just some background real quick. I recently moved from a house with a 200 amp main and had this hooked up. I am now in a house with a 100 amp main and want to do this without the expense of upgrading right now.

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As long as your panel will accept half size, AKA tandem, circuit breakers, sure you can add the 60 amp breaker, which may be available in half size also.

I am sure you are aware that the 100 amp service may not be sufficient to handle this added load along with the existing load, operate at your own risk.