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Answer for Canada, USA and countries running a 60 Hz, 120/240 volt, split supply service.
The main distribution panelboard has to have a main disconnect. This has been in the electrical regulations since the late 50's.
If the sub panel is in the same home under the same roof line, the sub panel enclosure does not need a main disconnect because it is just another branch circuit. Connecting a sub panel to a separate free standing garage or workshop is a different scenario and is governed by a different set of electrical code regulations.
What needs to be done to the panelboard is physically remove the neutral bonding screw. This is the screw that bonds the panelboard enclosure to the neutral bus. By doing this it stops a secondary ground pathway for a fault current from the sub panelboard to flow back to the main panelboard on the sub panel's neutral feeder.
The electrical code requires that there is only one position on an electrical distribution service where the distribution enclosure and the neutral bus join each other. That is at the main disconnect of the first over current device, which is the main service disconnect breaker or a fused disconnect switch whichever your system uses..
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What is a sub panel?
A sub-panel is always fed from a main panel. The main panel is situated where the electrical service wiring first enters the main structure on a dwelling plot or building site.A sub-panel can be situated within the same building as the main panel or it can be in a subsidiary building or structure (such as a garage, garden shed or workshop) that is separate from the main building.More informationA sub-panel is another name for a secondary breaker box, just as "the main panel" is another name for "the main breaker-box"."Breaker-box" and/or "panel" are just alternative short names that are used instead of the full name "circuit breaker box".
How do you connect 200amp from main panel to sub panel to the lug of the min panel to lug of sub panel?
Not exactly sure what your question is and you need to make sure you are in compliance with electrical code for your jurisdiction. But, generally speaking you install a large breaker (let's say 100A 2 pole breaker to power the sub panel) just as you would install any other breaker in the presently used (hot) panel, and the proper sized cable then goes from old to new and terminates on the main lugs of the new panel. Ground and neutral are usually isolated from each other in the sub panel but depends on other factors as to location of the sub panel, etc.
What size breaker do you use for a 100 amp sub panel?
A 100-A sub-panel would be fed from a 100-A breaker.
Can you put a 60amp breaker and a 50amp breaker on a 60amp subpanel just as long as they are not being used at the same time?
You can. Using these size breakers in a 60 amp sub panel might be pushing the limit for breaking the sub panels feeder breaker. The breaker feeding the sub panel will have to be no bigger than 60 amps because of the main bus bar capacity of the sub panel. It would be better to install a 100 amp sub panel and then there would be a bit of a buffer and you will have the ability to add additional small load circuits.
What should you do if your 200A breaker panel is full and you need to add three forty amp two pole singal throw breakers?
First you need to determine if addition of the new breakers will exceed the 200A service under normal operating conditions. If so you will need to go to power company and increase service and put in a larger main panel. If you have the capacity for the extra current you can add a sub-panel and add the breakers there as well as the breakers you will remove from main panel to accommodate the sub-panel breaker. Another way depends on what breakers are in current panel. There are some breakers that can be duplexed in the same space as a single breaker.
