Hi Reza,
Thank you for your response. Yes, we are making sure to ground the switch as well. Our concern with this configuration is with the possibility of the positive DC input being tied internally to ground (because of it being specifically called out as a -48VDC power supply and not just your typical +48VDC power supply...understood that it stems from the telco standard). If the positive DC is tied internally to ground and then with the return of our source being tied to ground, this creates a short circuit. As long as the positive DC input is not tied to ground in the power supply, we believe it should be fine that the return of our source is tied to ground; the power supply just won't care as long as it is seeing the proper polarity across its input terminals. We found in an installation writeup on the web site that it is considered to be DC-isolated (DC-I) but we understand this as only meaning that the DC output is isolated from the DC input; not necessarily that neither inputs are not tied to ground. Do you happen to know whether or not the positive terminal of this -48VDC power supply is tied to ground?
