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Solved problems · Electrical · Crew answer

What does the reverse polarity light on my boat mean?

A reverse polarity light or alarm means the hot and neutral, or the ground, aren't where they should be. Unplug and don't use that pedestal until it has been checked.

Symptom

The reverse polarity indicator on the AC panel glows or an alarm sounds when you plug into shore power, sometimes only at one marina or one pedestal.

Likely cause

The indicator watches the relationship between the neutral and the grounding wire. It lights when the hot and neutral are swapped, or when the ground or neutral is missing or faulty. The fault can be in the dock pedestal, a damaged shore cord or adapter, or wiring on the boat. A reversed connection can leave switched-off equipment live and turn metal parts into a shock hazard.

Stop now if

The indicator lights, anyone feels a tingle from metal fittings or the water, or a cord or plug is hot. Turn off the boat's main shore breaker, switch off the pedestal breaker, then unplug the cord at the pedestal first and at the boat last. Don't use that outlet until a qualified electrician has checked it. Never swim near docks or boats plugged in to shore power, because stray current in the water can paralyze a swimmer (electric shock drowning). A swimmer who feels tingling should swim back the way they came, where it should ease, and get out of the water as quickly as possible, avoiding metal ladders and rails, because touching metal can increase the risk of shock. If someone in the water seems shocked, don't jump in: cut the dock power, call 911 and throw a life ring.

The fix, in short

  1. Disconnect in the safe order. Turn off the boat's main shore breaker, then the pedestal breaker, then unplug at the pedestal first and at the boat inlet last. To reconnect, keep both breakers off, plug in at the boat first and the pedestal last, turn on the pedestal breaker and then the boat's main breaker, and check the polarity indicator before switching on anything else.

  2. Tell the marina. Report the pedestal. If other boats on the dock are plugged in, the fault may affect them too.

  3. Try another known-good pedestal. If the light stays off on a different, known-good outlet, the problem is likely the first pedestal. If it lights everywhere, suspect your cord, adapters or the boat's wiring.

  4. Inspect cords and adapters. Look for damaged plugs, burnt pins and homemade adapters. Replace damaged cords rather than repairing them. Never use a cheater or 'reverse polarity' adapter to make the light go out, and never cut or bend the ground pin. Use only UL-listed marine cords and adapters.

  5. Have an electrician check the boat. If it follows your boat, have an ABYC-certified marine electrician check the inlet, main breaker, panel wiring and the indicator itself.

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Shore power: Dock pedestal, shore cord and adapters, boat inlet, main breaker and AC panel reverse polarity indicator

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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