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.
