Why Did My Cabin Lights All Stop Working?

Don't let the scene behind your breaker panel overwhelm you. Focus on the one circuit that's not working, and approach it logically.

28th March 2014.
By Ed Sherman

Question: The photo I sent in is the scene on my boat when I open up the electrical panel board. I’m trying to figure out why all of my cabin lights stopped working at once. No way all the bulbs could quit at the same time, and the circuit breaker isn’t tripped either.

It may look like a scary bowl of spaghetti, but there's a logic to it.

It may look like a scary bowl of spaghetti, but there’s a logic to it.

I have always thought I was at least somewhat knowledgeable about electrical things, but as I stare at this pile of spaghetti, I realize I don’t know where to begin. Any advice on how to approach this problem would be greatly appreciated.

Answer: Well one thing’s for sure — that is a good sized bowl of spaghetti! Don’t feel embarrassed either — it is intimidating. You don’t tell me whether your boat is power or sail, but it doesn’t matter, the electrical circuits don’t know or care what type of boat they’re installed on. You need to focus your attention here on the one circuit that’s giving you trouble, in this case the cabin light circuit. But first, you need to consider the key elements for all electrical circuits on board boats, whether powered by a battery or shore power, it makes no difference.

The key elements for all circuits on boats are:

  1. A source of power (shore power, battery, solar panel, generator)
  2. Over-current protection for the circuit (a fuse or circuit breaker)
  3. A switch to turn the circuit on and off (sometimes one with a circuit breaker)
  4. Conductors (wires, buss bars and the like) to distribute the power through the circuit
  5. A load or device (why are we building this circuit anyhow?)
  6. A return path to ground back at the source of power

Your job as marine electrician is to locate all the components above in your troubled circuit and see which of the parts of the circuit are not functioning as they should. Forget about all that extra spaghetti and focus only on the circuit with a problem at the moment.

In this situation you need to find the DC negative buss bar. It will be the terminal strip with a lot of black or yellow wires going to it. Do not confuse this with a shore power terminal strip with black wires going to, it since those would be AC hot wires at 120 volts! It looks like the buss bar in question is in the upper center of the photo you sent in. Now if all the other circuits on your boat seem to be working OK, then that is a good indicator that your source of power, in this case the battery(s), are getting power up to your panel board. So that means the power is not getting from the panel to your lights. Start with the simple: First look for loose or disconnected wires, and for signs of corrosion at the termimals. If all seems well here, you may have a bad circuit breaker, assuming you’re sure that the breaker is turned on. Find the connection lugs on the back side of your breaker labeled “Cabin Lights” on the outside. Check for 12 volts on both sides of the breaker with the breaker turned on. If you have power on the line-in side of the breaker that is connected via the silver buss bar in your picture, and you do not have 12 volts at the line-out side where the red wire is connected, your circuit breaker is faulty and needs replacement. Make sure the replacement has the same amperage rating as the one you are replacing.


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About the author:

Ed Sherman

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Ed Sherman is a regular contributor to boats.com, as well as to Professional Boatbuilder and Cruising World, where he previously was electronics editor. He also is the curriculum director for the American Boat and Yacht Council. Previously, Ed was chairman of the Marine Technology Department at the New England Institute of Technology. Ed’s blog posts appear courtesy of his website, EdsBoatTips.
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http://www.EdsBoatTips.com

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