You can use the ComBus Quick Tester, a digital volt meter, or similar tool to test the N2 bus. In order to perform the test you need to disconnect it from the supervisory controller. If using the ComBus Quick Tester you simply plug the Phoenix Contact connector into the tester and start the process. If using a digital volt meter you need to measure the voltages between each of the legs of the N2 bus.
According to the documentation that comes with the ComBus Quick Tester the guidelines for a successful test are:
to Ref VDC 2.45 -3.00 will pass
to Ref VDC 1.90 - 2.54 will pass
to - VDC 0.38 - 0.92 will pass