Thread: Mystery wiring
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Old 05-13-2019, 12:26 AM   #1
City: Clearwater, FL
Country: United States
Vessel Name: Seas the Bay
Vessel Model: 1981 42' Hardin Europa
Join Date: Aug 2016
Posts: 681
Mystery wiring

I've had my present boat, a 1981 trawler, for about 5-6 weekends and a very small few whole weeks and am still going through everything and ran into a mystery.

An exterior 120VAC outlet wasn't working and I traced what seemed to be the problem back to the black wire being disconnected at a wiring block in the engine room that was labeled 120VAC.

I figured water was probably leaking into the outlet so a PO disconnected it. I took the opportunity to upgrade it and the other outside outlet to GFCI with new enclosures. But, this one outlet wouldn't reset.

I went to the engine room and put a meter on the terminal block wires. That's when things got weird. Green, yellow, black 12 AWG wires.

-- 16.6V **AC** green to yellow
-- 1.5V **AC** yellow to black
-- 14.64 **AC** green to black

Also observed:
-- No meaningful DC component measured.
-- Turning off one of the 120VAC outlet breakers makes the voltage go away
-- No other breakers make a difference
-- The other outlets on that breaker work fine.
-- I called the PO and the PPO representing 15+ years of ownership. They know nothing about it and think it is really strange.

Not yet measured/observed
-- It seems that there could be at least one thing on that circuit I don't know about, so there could be more.
-- Behavior under load
-- Waveform
-- Current on circuit with nothing plugged into outlets.

This trip is actually a carpetting trip, so I don't have a current clamp for my meter or my oscilloscope on me. I'll bring those next time. So, for now I just wired the outlet to known-good power and it works fine.

I obviously need to chase that wire next trip. Until then, anyone have any ideas what on a boat,might show AC voltages like that? I was thinking maybe something like a doorbell transformer, but those are, I think, 24VAC.

gkesden is offline   Reply With Quote