We had a VERY close call with the shore power cords on our boat this week! On Thursday, it was a rainy blustery day here in South Carolina. I was at home working on some inside projects, and my Yacht Protector system started pinging me that the Shore Power to the boat was going on and off about every 30 minutes.

The marina is still recovering from the flooding earlier in the year and construction is going on, also we’ve had some pretty heavy rains and a king tide so the parking lot where the power transformers for the docks are are under water again. I ignored the alerts since the power was coming back on, figuring it was just something transient.

About 3:00 in the afternoon, the rate of alerts picked up to about one every few minutes. I tried calling the marina to see if they knew about any issues, but as it’s the off season and a rainy day, they had closed early. So, I put on my raincoat and drove down to the marina to check out what was up with the power to the boat.

And am I glad that I did! I opened up the door to the boat and was greeted by a burning fiberglass and hot electrical smell. Immediately panic set in! I took a quick look/smell around the boat checking in the forward area where I had a fan (which was not running) and it was obvious that the issue was with the A/C power (rather than something running off the battery). The boat Air Conditioner/Heater fans were still running, but there was no 110v A/C power. I went out to the dock, and checked that the power cords were still attached, and switched off the main breaker until I could find where the issue was.

I checked the electrical panel, no smell there, checked the engine room, no significant smell there, then opened the lazarette (storage area in the back of the boat where the generator is located) and was almost bowled over by the smell and there was a slight smoke haze drifting around in there.

The power cords for our boat come from the shore side, run down the length of the boat, and plug in at the back. The cords are “twist-lock” and have retaining rings that screw in to hold them. When we use the boat, we disconnect the shore power side, and leave these connected all the time.

I checked the two circuit breakers located directly under the plugs and both breakers were still on.

These types of plugs are notorious for getting hot and the contacts arcing if they are not correctly seated or too much of a load is put on them, so that was my next check point. I disconnected the left plug which runs the Air Conditioning system and inspected the plug and cord end. Both were fine.

Next I unscrewed the House Power side, and tried to twist the plug to remove it. It wouldn’t budge! I pulled and twisted harder and finally just gave it a good tug, and it came out. It was totally blackened and melted.

One of the contacts (the hot lead) had completely melted away. Realizing that this was the issue, I grabbed a screwdriver and removed the receptacle to check it out.

The entire plug inside the transom of the boat (which is all fiberglass) was burned away. There had been a pretty major fire in that plug as more than half of it was burned completely away. I consider ourselves SO LUCKY that the fiberglass on the boat didn’t catch on fire and destroy the entire boat.

Given that it is off season, and rainy windy day, there was no one else around the marina, so it would have been some time before anyone saw it to report it.

I took a run to West Marine and Home Depot to get repair parts, and a new shore power cord. And in the rain and wind, Brenda and I replaced everything from the circuit breaker on the boat, up and we had power again.

What the heck happened?!?!

Here’s the lesson to be learned from our close call. There were a number of contributing factors:

  1. We almost never checked the connections. Over time, they had come loose allowing arcing. We’ve now added it to our docking routine and periodic boat inspections to check the connections by removing them and inspecting the contacts.
  2. There was no strain relief on the boat side. Even with the retaining rings, pulling on the cables taking them on and off the boat when we used it caused the connections to become loose. So, now we have strain relief. I’m also checking into the “SmartPlug” cord connectors which claim to be much better connections that twist locks.
  3. I was stunned that the breakers didn’t trip. On the shore side, we have a 50 amp 240v cord with a “Y” adapter that splits it into two 30 amp, 120v circuits. So even though the cable is rated for 30 amps, the breaker that’s serving it is rated to 50 amps! More than enough juice to fry the connector. Many marinas (like ours) only have 50 amp connectors not 30 amp, so the use of adaptors like ours is common. Even a direct short on one leg of the 50 amp may not be enough to trip the shore side breaker. There really isn’t a good solution to this aside from being very careful, and making sure that you don’t overload either leg.
  4. The 30 amp circuit breaker on the boat, is AFTER the plug connection, so it didn’t even see the load when the plug started to short. Newer boats have an ELCI (Similar to a GFCI common in homes) that detects shorts and cuts the circuit which would probably have tripped. I’m investigating installing these.
  5. The temps here in South Carolina are starting to go down. We’ve had a few nights in the 30’s. Last year, we had a few weeks of cold weather and the heaters on the boat iced up when the water got cold (we had ice on the water around the boat). In order to prevent this, I purchased two heaters one boat specific for the bilge, and a standard oil-filled radiator style. I had these both plugged in. After the repair, I checked the load with the battery charger, water heater, and the two extra heaters, and it was right at 28 amps. Not enough to trip the breaker, but enough draw to cause the plug to melt without a good contact.

So, lessons learned! In doing some reading, I found a statistic from Boat US that 55% of boat fires are caused by shorts and overloading of shore power cords. Yikes!

Please everyone make it part of your regular routine to check your power cord connections. We almost lost our boat! I’d hate for anyone to experience the same thing.

Tom & Brenda