I'm getting confused now... can't keep track if you're responding to charly or Jeremy. Jharkin's problem is load balance, combined with a bit of under voltage (224V) at the mains. Charly's problem, at least the way he described one circuit dragging down a separate circuit, is also at the mains. In both cases, when checking mains voltage, try to get the probes right on the little bit of exposed main wire, right above the main breaker/knife switch lugs. Measuring on the lugs themselves will be affected by possibly loose or corroded lugs. A loose breaker or receptacle lug can be frustrating, as they may not get hot enough to trip the thermal mechanism in the breaker, particularly if its a cyclical load at the end of a long branch circuit. We had a window AC in a bedroom in the house where I grew up, and it would run about 12 hours before tripping the breaker. It took a while to figure out the problem was a too-loose receptacle, which took about 12 hours to transfer sufficient heat down the copper wiring to eventually trip the breaker. Potentially dangerous situation, but has nothing to do with either of the problems I read here.