Solution:

As of 10/2008, the shield of the RJ45 on these products is directly tied to the ground of the power supply input. This means that customers with positive ground systems (for example, running off negative 48 volts) will cause a short circuit if they use a shielded patch cable to connect our device to another grounded device on the other end. For customers with positive ground systems, they should not use shielded patch cables.