If you will notice, your individual breakers add up to much more than 100amps. So it is entirely possible not to trip an individual breaker but still draw more than 100amps, which would cause the main to trip.
If you haven't had this problem in the past, I wouldn't worry about it unless it happens again. If it does, you need to upgrade your service to more amps.
It is entirely possible your main breaker has malfunctioned but that is not easy to test. If it is replaceable, and if you have further problems, you can consider replacing the main breaker to see if that fixes the problem. That is much less expensive than upgrading the service.
A short, which will trip the main breaker.
only if listed in the panel board
If you are talking about a breaker in a house panel then a 15 amp breaker would be used. It is the smallest amperage breaker that you will find in a house panel.
The biggest circuit breaker in any home is the main breaker located in your main breaker panel that is installed where your electrical service cable comes into your home.
Look to see if the 30 amp panel is fed with a two wire or a three wire. If it is a two wire then you are out of luck. If the panel is fed with a three wire then the panel should have the neutral terminated in the panel. It is this neutral that you need for 120 volt connections. You didn't state how many panel slots there are in the panel. If you are able install a 15 amp breaker into the panel and connect the wires going to the load. The black wire will go to the breaker and the white wire will go to the neutral bar in the panel.
A short, which will trip the main breaker.
The panel and breaker have to be of the same manufacturer. This way the breaker will fit into the panel. If the panel has a push in bus bar, the breaker must also be the type to accept the bus bar. If the bus bars in the panel are of the bolt in type then the breaker also has to be a bolt in breaker.
It is inserting a breaker into a service panel.
only if listed in the panel board
No, a Cutler Hammer will not work in a GE panel or vice versa.
A 100-A sub-panel would be fed from a 100-A breaker.
If you are talking about a breaker in a house panel then a 15 amp breaker would be used. It is the smallest amperage breaker that you will find in a house panel.
Possibly. Depends on which model Siemens breaker you have.
The biggest circuit breaker in any home is the main breaker located in your main breaker panel that is installed where your electrical service cable comes into your home.
5'6"
In North America the smallest size breaker found in a home distribution panel is rated at 15 amps
Look to see if the 30 amp panel is fed with a two wire or a three wire. If it is a two wire then you are out of luck. If the panel is fed with a three wire then the panel should have the neutral terminated in the panel. It is this neutral that you need for 120 volt connections. You didn't state how many panel slots there are in the panel. If you are able install a 15 amp breaker into the panel and connect the wires going to the load. The black wire will go to the breaker and the white wire will go to the neutral bar in the panel.