Hot Spots

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Years ago I was working in the lazarette on a hot day when I glanced up and saw a red LED illuminated on the DC panel. Normally, the Mastervolt DC distribution units have only green LEDs. I could still see the green LEDs on as usual but we also had a red light. I stopped to investigate and found that the “red LED” was actually a bolt that connects the two bus bars together. It was a full turn loose and so hot it was glowing red. The picture below shows what it looked like once it had cooled down. The bolt, circled in red, was so hot it had burned off the galvanization.

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After shore power connection problems, this sort of fault is the most common cause of boat fires. High-current electrical systems can draw a lot of amperage at 24V (and twice as much on 12V boats). In this case, the air conditioning system was running, so the electrical consumption was on the high side, so the current was high, and the heat from this loose connection was dangerously high.

The lesson here was one I already knew from my working life but had failed to apply at home: new electrical systems need a re-torque after 1 to 2 years. In fact, it’s good practice to check high-current connections periodically to make sure they are still properly torqued. Mobile systems can vibrate loose, and some electrical components vibrate and this can loosen fasteners as well. It’s an easy problem to check for and an easy one to avoid.

As a further safety step, I use a FLIR One Thermal Imaging Camera to spot bad connections. Every six months, we walk through the boat shooting the DC Panel, the breaker panel, the shore connections and breakers, and any other electrical connections. If any high temperature connections are found by the FLIR, open up the panel or equipment and investigate more thoroughly.

Below is an example of the DC panel on Dirona where all the manual transfer switches are in their normal position and running at fairly low loads except the 6kw, 240V inverter which is running at very near full load.

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Note how clear and easy to see the increased temperature around the Blue Sea System manual transfer switch for the 240V inverter. In this case it’s flowing at just over 200A on a part rated for 600A continuous and 900A short duration. Incidentally, that’s why that one rotary switch is gray whereas the rest are red. Those red parts are only rated at 350A continuous and, to have engineering safety margin, we went with a higher rating for the 240V inverter.

The FLIR can also show unusual heat on shore power connections. Another common failure point that we have seen on Dirona are power sockets that make less positive connections over time. We also shoot wall connections under load with the FLIR to find any unusually warm sockets. Here’s an example of a 120V appliance socket that has failed due to excess resistance at the connection (low tension in the spring connectors):

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The FLIR is also excellent at finding lights left on in cabinets, poorly insulated hot water pipes, and air leaks to the outside. It’s a super useful and fairly inexpensive (<$200) addition to any household that will help eliminate the risk of fire due to high current electrical connections with poorly torqued or aging connections. It’s low-cost insurance.

Because the current flows are high on both shore power connections and low voltage inverter feed wires, I recommend checking them frequently. And, if you have never re-torqued your DC electrical panel, it’s worth doing it right away. High currents can be dangerous if the electrical system is not properly maintained.

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16 comments on “Hot Spots
  1. Tim Talbott says:

    Hi James: Tim on Piredmus N63-06….on the FLIR website, it says the “scene temp range” at the upper end is 120 deg C or 250 deg F. I would have thought this to be too low for the serious things one would be attempting to find on the boat and particularly in the engine room while under way. Do you find that the temperature range is reasonable enough to do what we need on a boat and to find any issues that may be showing themselves?

    • I only use it for electrical issues or temperature leaks and it’s great for both. I agree the range is too low for mechanical systems. For those I use a digital IR heat gun. It has a laser sight that shows the focus point. I find it useful to check fan bearing temps, exhaust runner temps, coolant temps, etc. More expensive FLIRs can cover these as well but the low cost one I’m using doesn’t have the range width and I kind of like the digital IR gun.

  2. Timothy M. Daleo says:

    Thank you for another good article James. I just ordered the Gen III from FLIR and will be trying it on my boat next weekend!

  3. David Magda says:

    An observation that came to mind when looking closer at the DC panel picture: in a “standard” running configuration, different switches are in different positions.

    It reminds me of a neat UX feature of Airbus’ A220 (nee Bombardier Cseries) flight deck: all switches will be in the 12 o’clock position for normal operation, so a simple glance of a panel will show if things are as they ‘should’ be, or if something is in a non-standard configuration.


    Kind of a “well, duh” no-brainer design idea once pointed out, but I think that I’ve seen in very few places in practice.

    • It’s a good idea but once the wires are installed, it’s close to impossible to swing these switches 90 degrees. What I did after delivery is label the only connections that aren’t normally on at 12 oclock as “normally off” to make it more clear. The Airbus solution is a better one especially when surveying large panels. This video at about 2:15 seconds in shows the solution we use on our breaker panel: Here we use colored wire ties to show the “normal” position for different operating modes.

      • David Magda says:

        Yes, unless one was doing a complete ‘reno’ of a boat’s electrical system it’d probably not be worth it; though I hope it’s something manufacturers perhaps become aware of.

        For the breaker panel, again something perhaps for OEMs: maybe organize switches so the ones that are typically used while underway are clustered closer together. Your coloured tags are a clever idea, but it seems that you have to jump around the panel a bit, and it may be better if those would be clustered closer together.

        P.S. For YouTube timestamps, you can have “&t=2m15s”: I’ve found it much easier than trying to count seconds. :)

        • On the breakers, many of these that belong on are unique to the boat. I put on one steering pump but chose not to power the other since I want the backup pump not to be worn out. For years the right breaker underway was Autopilot #1 then it went to #2, then back to #1, and now it’s back to #2. It’s kind of unique to the boat and how the redundancy of systems is laid out. Some boats chose to only have a single autopilot pump. My approach is to turn the running lights on when underway and turn them off when we stop. This ensures they are always on in restricted visibility but, for some people, they prefer to only turn them on at night. This is an operators choice. Some gear that needs to be turned on is part of the 12V panel and some part of the 24V panel so getting them together is more of a hassle. Because those that need to be on underway are all tagged with yellow, I can get them on only a couple of seconds and the difference between having them together or appart is slight. I personally don’t mind it as is.

          I like your suggestion to line up all the manual transfer switches in the “Normal” operating mode. Thanks for the tip on the time offset for Youtube. I didn’t know about that one.

  4. Steven Coleman says:

    Check the green however, checking torque every periodically is pretty much an industry standard.

    • Thanks Steve. That does make sense. David Magda asked about thread locker below and my inclination was not to use it but, as a post torque addition using wicking green Loctite it seems likely that the electrical characteristics of the connection would be unimpaired.

      • Steven Coleman says:

        Yes I was posting that for him just didn’t hit the reply button, it’s actually not the conductivity of the actual bolt that is a concern but the contact surfaces of the buss the bolt is compressing together. I can’t think of any bolt not made out of copper or several other soft materials with the conductivity to meet UL requirements (standard for the US other countries either accept or have thier own), and yet be strong enough to torque two buss connections together but, that’s not an area I’ve ever researched.

        Any bolted surface which expands and contracts due to thermal factors is going to be prone to becoming loose and should be checked for the correct amount of torque at least once in it’s lifetime.

        While I wouldn’t have any idea why a thread locking product properly applied to simply the threads would be illegal for use in electrical connections, I also don’t see any real benefit either.

  5. David says:

    Excellent post and very good feedback. Ordered the FLIR moments ago! Had been waffling on getting it but the safety reasons you suggested pushed me over the edge!

    • You’ll also find it interesting in showing air leaks on your boat. Areas where outside air is getting in. I only use the Flir every 6 months but I find it useful mostly as a relative measure showing you differences that need to be investigated further.

  6. David Magda says:

    Can thread-locking goop be used on electrical connection bolts or would it interfere with conductivity?

    • I have never used thread locker in this application and relied on torquing but it’s seems like an idea worth investigating further. In my looking around I found an article from Loctite on what thread locker to use on electrical connections ( and another article that claims you should never do it and it might even be illegal ( The latter article sounds a bit extreme (may not be legal) so may not be credible. The key concern is that the thread locker may insulate. I would think if it’s only on the threads and the face of the nut is clean, it shouldn’t be a problem. But because of the resistance concerns flagged in this article, I think I’ll continue not to use thread locker on electrical connections.

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