Replace 200 amp breaker

200 amp is 3/0 copper wire up to 100 feet.
Use size 250 wire up to 150 feet.
Use size 350 wire up to 200 feet.
Be sure to put wire in conduit.
http://waterheatertimer.org/images/Wire-size-and-amp-chart-700.jpg
http://waterheatertimer.org/How-to-install-a-subpanel.html
http://waterheatertimer.org/See-inside-main-breaker-box.html

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Copy following links for general illustrations and information:
http://waterheatertimer.org/How-to-install-a-subpanel.html
http://waterheatertimer.org/Troubleshoot-household-electricity.html#stress
http://waterheatertimer.org/See-inside-main-breaker-box.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

This looks like an indoor panel. If you have an outdoor panel next to (or below) the power companies meter, It should have the breaker to feed such a panel. Thus, this indoor panel should only be required to have "main lugs" to receive wire from outside breaker. NEVER size breaker outside bigger than the equipment rating of inside devices. If from the power companies meter you intend to feed this panel, YES it is required to have a Main Breaker.

This work requires a license (or qualified person) everywhere that the National Electrical Code is enforced.

If you're asking how to wire a single phase 200 amp panel from a larger, 3 phase panel of the same voltage - ONE way is to install a 2 pole - 200 amp breaker into the 3 phase panel. Provide 4 correctly sized conductors with the correct insulation in a cable or conduit between the 3 phase panel and the 200 amp single phase panel. Two of these conductors should be black and red (for 120/208 volt system) and connect to the 2 pole - 200 amp circuit breaker terminals, the third should be white and connected to the neutral bus bar. The forth should be green and is connected to the neutral bus bar as well but *only if* it is "service equipment" If it is a "main or sub panel", the green wire should be connected to the ground bus bar. The other end of the conductors should be terminated in a "main lug only" 200 amp panel. The back and red connect to "line 1" and "line 2" bus lugs, the white to the neutral bus bar that is NOT electrically connected to the panel enclosure (do not install the screw or strap between the bar and enclosure). The green must be connected by installing a separate bar that is securely fastened both mechanically and electrically to the enclosure for ground connections.

There is a great deal going on here - and plenty of variables that can change how to do this work, safely and correctly. This is an example of just ONE of many different ways to do the work for a particular installation. There is no one way that works for all situations. If your situation does not support this method - you will have an unsafe installation and subject the building and people in it to a dangerous fire / safety hazard.

Please, consult a licensed electrician before attempting this work.

Do you have a Square D "QO" panel - or a Square D "Homeline" panel (or a different brand panel completely)? If possible, please provide the catalog number of the circuit breaker.

Nearly all circuit breakers that are TRIPPED (handle is at the midpoint between ON and OFF) must be RESET by pushing the handle to the OFF position - then pushed the other way to the ON position. A circuit breaker that is in the OFF position, does not need to be RESET, and need only be pushed to the ON position.

It is advisable to shut off ALL the other circuit breakers in the panel, then turn on the 200 amp breaker. After the 200 amp breaker is on, turn on the largest value (in amps) double pole breakers and finally all the single pole breakers largest values down to 15 amps. This prevents switching one very large load all at once.

What is your voltage reading coming into the panel?

I need a liitle bit more info of the house. Total heated square footage and what appliances are electric?

Well breakers can weaken overtime if they are overloaded. A breaker is meant to have 80% of its capacity used, for example a 20 amp breaker should have only 16 amps of current on it. If something was changed six years ago that has loaded that breaker to its max it may have not affected it until now. Another thing would to be absolutely sure that everything running in your house is not exceeding 100 amps. Many houses these days have 200 amp panels because of how much amperage added appliance and the like will use. A licensed electrician will be needed to swap out the breaker, which will be a little expensive but shouldn't be outrageous as he will not be swapping out the whole panel, just the main breaker.

This is a sub-feed lug, should you ever decide to add a sub-panel in your house. So when landing your feed wires to this panel, use the larger lug. Good Luck, and feel free to ask me anymore question's that you may. - Jim

no, not to code plus the expense would not justify , you can purchase the 200 amp panel with the main already installed cheaper than purchasing the 200 amp breaker in most cases and still meet the code check on a panel package called a home owners kit ge makes one square d , makes one either good quality , you get the 200 amp panel, several breakers such as 20 amp 50 amp 30 amp by far the best route for you