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Marine Electronics Journal Blog

Thermal imaging as a diagnostic tool

Because some boaters like to know as much as possible about their mechanical and electrical systems, occasionally we serve up technical advice that might help when installing a device or troubleshooting a problem. This week it’s excerpts from a column written for Marine Electronics Journal by electrical guru Ed Sherman. He’s vice president/education for the American Boat & Yacht Council (ABYC) and also writes a blog called Ed’s Boat Tips.


By Ed Sherman


During our combined ABYC/NMEA certification classes, one of the things that I typically try to drive home to the technicians is the fact that excessive electrical resistance will always manifest itself as heat. Sometimes this heat is enough to actually cause fires. The problem is that often this heat goes unnoticed until a complaint arises about poor performance from a piece of electrical or electronic equipment. For some time now, I’ve been using a thermal imaging camera to look for excessive heat in electrical systems. (Photo at right courtesy of BoatUS.)

How much is too much?

The question becomes how much heat is too hot? For years I’ve used a 25°F rise in temperature as a personal benchmark and it has worked out just fine. But, for the purposes of this article, I decided to do a little research and see if there was a more relevant specification available. I found a 2002 bulletin from Square D entitled “Wire Temperature Ratings and Terminations.” In the bulletin they use a differential of 15°C as a benchmark. They also make this statement, which sums up the point I’m trying to make here: “If a termination is rated for 75°C, the maximum temperature at that termination is 75°C when the equipment is loaded to its ampacity (defined as the maximum amount of electric current a conductor or device can carry before sustaining immediate or progressive deterioration---Ed.). If 60°C insulated conductors are used in this example, the additional heat at the connection above 60°C could result in conductor insulation failure.”

Possible wire sizing issues

I’ve been advising technicians for years that we have typically used 105°C-rated boat cable in our installations but that they should be using the 75°C ampacity column from the ABYC Standard E-11 to be safe. I suspect that field technicians might adhere to this guidance but that boat builders would probably not due to the cost differential in the wire gauge that is implied. All of this is most especially true with onboard 120 and 240-volt installations. Based on my own observation over the years that boat owners typically load up their shore power and onboard generator- or inverter-supplied AC systems to the maximum they can squeeze out of them, I’m sticking to my own advice. Temperature differentials do matter.  

Interpreting what you see

Historically, thermal imaging equipment was priced so high that most field technicians simply couldn’t consider purchasing it, $15,000-20,000 was just a bit too big a financial bite. The return on tool investment just wasn’t there in most cases. Our friends at FLIR changed all that; the handheld unit I use, their I-7 model, cost $1995. FLIR now sells a unit that attaches to either an iPhone or Android phone called the FLIR-One for around $200. The key to using the tool is knowing how to interpret what the device is showing you. Dramatic color changes on the display screen may look like a big deal with potential danger lurking, but that simply may not be the case. The photo below is a prime example of what I mean .

The colors go from a dark blue (cool) color to a bright yellow (hot). The color differential at first blush seems pretty dramatic and could be interpreted as indicative of a problem. Well, maybe not based on what I’ve been using as a benchmark or what Square D has identified. A 17°F differential is really not that big a deal. The bottom line with thermal imaging is that it’s gotten so good you can pick out one bad terminal on the back of a loaded panel board or inside a plug assembly, but use the temperature scale and the selection cursor when working with the software that is provided with your camera.  















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Comments | Leave a Comment
Page 1 of 3 ( 11 comments)

Hard-Over with Brushed APilot Pump:(12/18/2017 5:37:05 PM) "Jim.
What do you mean by ...."Garmin GHP 20 with SmartPump...Because it is a brushless system, it is fail-safe and won’t execute a hard-over turn the way a brushed pump can."

Thanks for the note. Since the description came from Garmin I contacted the company for an explanation. Here's what one of their engineers told me:

On brushed DC actuators, a single-point failure in the drive circuit (shorted wire or blown component inside the controller) could cause the motor to run full speed in one direction and take the rudder all the way to one rail. A brushless actuator relies on timing-controlled commutation, so a short or component fail would cause the actuator to stop moving rather than moving at full speed.

Hope this helps,

trawlerdeejay:(10/13/2017 3:46:51 PM) "Excellent article. I had no idea what the differences were between o183 and 2000, Thank you so much."
Darryl:(3/27/2017 10:17:15 PM) "Putting the MSRP with each unit reviewed would have been helpful. If each unit was actually tested, the reports on each unit would have been helpful too.

Thanks Darryl---we generally don't mention prices due to confusion over so many variations---MSRP (mfg. suggested retail price), MAP (min. advertised price), MRP (min. resale price) and then there are internet prices on some websites that go their own way. But your point is well taken--buyers need to know if something is in their price range. We'll work on it.
There is independent testing of some of these products on sites like but the information we receive from manufacturers rarely cites the results of any shootouts they may conduct against the competition's products. "
Laurie Seibert:(2/16/2017 2:00:20 AM) "Thanks EV Collier for sharing this informative blog. It is important to know the causes of EMI filters. We use these parts in our daily life in the electronic products so we should know that what are the causes are cures of EMI Filters.

Great job and keep updating!

Laurie Seibert"
Yes:(2/10/2017 7:22:40 AM) "EMI/RFI filter causes and cure. There are very few people who share such information with everyone. I was looking to read such informative blog!

Great job!

Lisa Wilson
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