Yesterday evening I cut off the main power to check if a Siemens tandem 20A single pole breaker was going to fit my Siemens 200A panel in preparation for making a 10-3 UF run to my shed. The bottom two left slots are open. No wires were hooked up, the new breaker switches were in the off position. It fit fine, snapped in tight and easy in the next to bottom left open slot. I left it there and turned the main power back on. This morning I noticed my shower was not real hot. I checked the panel and the double 30A hot water heater breaker (bottom right) was off an the 20A above that was off too. I switched them back on. They didn't trip when I cut them back on. I don't remember cutting them off last night...guess i could have but had no reason to touch them. When I get home today, I am going to check them first thing to see if they are still on. Given the above situation, is there any explanation that would cause the other breakers to trip?