ETL Breaker Tests

165 VDC ETL TEST STORY (continued)
Rev: - Page 2 of 2
The third and most terrible test was a short circuit test rather than merely an overload test. If we had an
unlimited budget for power supplies and Grand Coulee Dam next door, we could have conducted this next
test with as little as 200 amps being shorted to ground. The short was to be done while running 99 amps
through the breaker. There is a 20 amp glass body fuse connected from the metal breaker box chassis to
ground. The breaker box, battery negative and the short are also connected to ground, so a 6AWG wire and
the fuse are in parallel from chassis to ground.
This test set up provided us with all sorts of problems. One of the problems was that I was not exactly
excited about putting a direct short across the 13 batteries! If the breaker failed, we would have our own
Chernobyl! Some other challenges were just how to accomplish the switching of power and then shorting
to ground. We cured the hook up and switching dilemma and proceeded to apply power after which we
immediately applied the short. Since we did not have 200 amps of power supplies available, we used the
full force of the batteries. We estimate that the current was about two thousands amps!
The goal on this test is to prove that the breaker will not arc to the case which would blow the 20 amp fuse.
Well, we blew the fuse numerous times and then called boB in to help figure out the problem. Sure enough
we had something hooked up wrong and the short was being run directly through the 20 amp fuse. Has
anyone ever seen what happens to a 3AG fuse after running two thousand amps through it? I’ll save you the
trouble. There is nothing left of the fuse. It exploded into a thousand little pieces. After hooking up the fuse
correctly, it was now placed in parallel with a 6AWG wire both connected to the ground busbar inside the
MidNite MNDC box and the other end to a conduit pipe in the building. We had better success, but on the
second breaker we experienced a blown fuse again. This test requires three short circuit tests to be done on
three separate breakers. The first passed just fine although I noticed the wires jumping off the floor during
the short. boB pointed out that the fuse and the paralleled 6AWG wire was connected about 8 feet apart on
the conduit. This provided just enough resistance and inductance to blow the 20 amp fuse. We passed with
flying colors after moving all the grounds together. Lesson learned. Tie all grounds together with large wire
and keep them as short as possible.
MidNite solar 150VDC MNEPV breakers are available in 10,15,20,30 and 63 amps.
Robin Gudgel
Pictured above, boB breaking 165VDC at 99 amps for the first test. This arc is the same arc that our little
breaker must deal with internally. The arc is not only blinding, but also extremely hot. Pretty amazing huh! I
also discovered the hard way that getting shocked with 165VDC feels pretty much the same as getting shocked
with 120VAC.