Definitely sounds like the SS was clamping. Maybe the SS thought a surge
occurred at initial startup of the power supply? And FYI, I have used
Traco TSP 48v supplies with -48 radios just fine, output is floating.
On 2/19/2016 10:40 AM, Adam Moffett wrote:
...my first thought of course was maybe it was hooked up wrong the
first time. The four 16ga wires hold their shape pretty well and I
didn't have to re-bend them to fit, so I'm pretty sure they were on
there correctly.
People talk about SS's "clamping" or "clamping to ground". Could that
cause a short? I never tested the power wires against ground.
If you're thinking +48 and -48 mixed on the tower, there are only two
devices on the tower right now. One base station and one backhaul,
and they're both -48. There's some 24v stuff in the enclosure at the
bottom (switch, site monitor), but none of those have a ground
referenced to power and they're isolated from the other stuff by a 48v
to 24v converter.
On 2/19/2016 11:27 AM, Adam Moffett wrote:
So I went out to a new location yesterday afternoon just to turn the
breakers on. The power co had just plugged in the meter a few days
prior.
The Traco 48v power supply there immediately went into an alarm
state. After some troubleshooting I found a dead short on the -48v
power bus (terminal blocks with jumpers actually). The short ended
up being on the power cable to a Wimax base station, I read 0 ohms
between + and - on that cable.
There's a Motorola 200SS surge suppressor within 5' of the power bus,
and then about 80' of wire to the base station. I checked resistance
between + and - on each side of the SS and read 0 ohms both ways.
There are actually 4x 16ga wires going to the top, so two were
screwed down to + on the load side of the SS and two on the - side.
That whole part was backstory. This is where the mystery starts.
I pulled all 4 wires off the load side of the SS to see if I could
narrow down which pair was shorted, and I couldn't find a short. I
checked the load side and the supply side of the SS and it was open
on both sides. So then I reconnected the wires to the SS and checked
again - no short. I plugged the BTS back into the bus...powered up
just fine.
So where did the short circuit come from and where did it go? In
hindsight it seems like it had to be in the SS or before it. If it
was shorted at the top there would have been > 0 ohms of resistance
with the 80' of wire.
