By chance I started checking the running circuit and felt a faint buzz on one of the relays. There should be no buzz here. This relay had a 220 VDC coil and with the safety circuit open there should be no voltage present whatsoever. The meter indicated around a 140 VAC. This car was an older Haughton ALNC with 220 VDC running circuit and above ground 208 VAC for most of the other logic. This was a throwback to the �Good Old Exciter� days. Fortunately the problem was right out in front of me; I just had to find it. I started pulling controller wire and checking the wiring diagram and low and behold there was a wire that didn�t belong on the DCLB relay. During the Fire Service upgrade we had added a new wire on top of an old wiring change. This wiring change was buried under a pile of old black controller wiring. It also wasn�t on the as-builts that engineering used to engineer the Fire Service revisions. This field wiring mistake plugged 100 VAC into the 220 VDC running circuit. This was not enough to energize the 220 DVC running circuit, but under certain conditions, this stray voltage could keep the running circuit powered up when it shouldn�t happen at all.
Great find, Christy!
I get so used to hearing buzzing relays, I've probably walked past a bunch of them without thinking twice. Good work!
