DVR-Security cameras fuse blowing.. no logic explanation

When installing additional sony dome cam (vc-ca-domir2850) the camera would not turn on and keep blowing a fuse in the powerbox where all the cams are connected. To test the camera we took a working camera from different location, plugged it in and it also blew a fuse. When we put back the working camera in its original location it still worked.
Second test was to plug in the extra camera into the location where the camera works (to eliminate the cabling issue). Again it blew a fuse.
Problem: when we hooked up a camera that used to work fine after the extra cam blew a fuse it started doing the same thing. Everytime we replace a fuse and make sure nothing is shorting etc.. turn it on - it blows a fuse in the powerbox. And before the camera worked just fine. We are really confused as to what could cause that. All cameras are compatable and nothing in powerbox is shorting.. and the + and - are in right places. Anyone had similar problem before?

Recheck the Voltage and polarity of your cameras and supply wiring. Most manufacturers' cylindrical DC connectors have + in the centre connection. Sony usually has + on the outside of the DC connector.