It's an unfortunate fact that certain loads draw a sudden peak of current when switched on which is many times greater than their normal current. A/C compressors, other large motors, and many other devices will tend to do this.

I'm located barely more than 200 feet from the transformer which feeds my house, yet I notice the lights dim momentarily when switching on a big transformer that I use to power some equipment. (For the ECN guys, it's 1000VA, 240V primary, 120V sec.)