This is a long post, but it’s worth the read… We moved to a different home last year. Part of the fun of moving to a new place is redesigning our holiday light show (yes the kid in me loves to light up the house!) At my old house, I had run two dedicated 20 amp circuits with Ground Fault circuit interrupter (GFCI or GFI) to power the show. My new house has one outside outlet so I stepped down the light show, but it kept popping the circuit breaker. I traced the circuit and it had a dedicated 15 amp breaker, which should have been enough, but I wasn’t sure – so I tried several times disconnecting more of the show.
I finally bought a Kill-a-watt* (newegg has them for $16.00) that you can plug in between your load (the lights) and the outlet that shows you how much current is being drawn – among other things. It was drawing 12.5 amps, which is a lot but still under the limit of the breaker. I never quite figured out the cause, until about 6 months ago my wife was walking down the property to pick up the kids from the bus stop. Suddenly She herd a “ZAP!” from under her feet. She looked down at her now blackened shoe and a puff of smoke. Apparently the previous owners had run a 120v line using indoor wiring that terminated above ground – just bare to the world just waiting to arc to anything that stepped on it! I removed this line and I’m thinking I will have better luck with popping circuits this year, and I reviewed the rest of the wiring for any other surprises.
A good read on “how much can I plug in” is here: http://lifehacker.com/software/safety/avoid-overloading-your-electrical-outlets-321652.php
*The Kill-a-watt is a killer (no pun intended) device to measure how much power things take (especially when they are “off”) to see if adding power switches or replacing bulbs with high efficiency CF bulbs will help you electric bill.