Unexpected cause of Dometic fridge fire discovered

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NOTE: Electrical expert Mike Sokol reports that this news story has inaccuracies, so please keep that in mind when reading it.

By Greg Gerber
RV Daily Report

SUN CITY, Ariz. — An RV technician trying to diagnose a problem with an older model RV watched as the unit’s Dometic refrigerator caught fire. His subsequent investigation traced the source to an electrical problem not related to the gas leak commonly cited as the source of refrigerator fires.

The flaw impacts RVs built in the mid-1980s to present with installed Dometic LP gas refrigerators, he told RV Daily Report. It is caused when RV owners attempt to use an adapter to connect a 30-amp, 110-volt RV to a 15-amp, 110-volt power source, whether in a campground or at home.

Adapter plug to allow a 30-amp cord to be used on a 15- or 20-amp power source.

Screen Shot 2016-08-03 at 8.10.52 AM

Many RV owners use adapters like the one pictured above, he noted. But, without proper power management, attempting to use an air conditioner and refrigerator together will cause the neutral lug in the plug to get hot.

Once this happens, the Dometic refrigerator control boards will melt down as the current seeks a new neutral connection, the technician explained. That causes the electricity to jump to the earth ground connected to the chassis via the incoming shore earth ground.

“Surprisingly, no fuses of any type blow and the Dometic control boards will catch fire,” he said. “Since they are made of plastic cases, they burn fast and quickly.”

fridge-754

Evidence the circuit board started burning can be seen in right side of the image. Even without an adapter, an RV park’s well-used shore power pole may have older burned up female plugs from the massive electric use required for things like air conditioning and microwave ovens, he noted.

“Many times we have seen the RV’s male plug’s 30-amp neutral side burned from bad connections caused by the RV not being bonded at the 110-volt box,” he explained. “This recipe for disaster is possible for any RV using the Dometic refrigerator prior to 2000, and possibly beyond.

“However, Dometic did replace the non-warranty board, heating elements and thermistor at my request for the customer,” he explained.

RV Daily Report consulted with two other experienced technicians, who both said it appears the scenario described above is plausible.

One of the technicians, Gary Motley, with Motley RV Repair in Oklahoma City, said he and one of his technicians analyzed the problem in conjunction with a review of Dometic’s home study course.

“Proper voltage and polarity are very important. This refers to 12-volt DC power as well as 115-volt AC power,” said Motley. “The use of a 30-to-15-amp adapter is not good when running an air conditioner.

“Over time, this can cause the connections to overheat and become corroded,” he explained. “When this happens, voltage can be lost over these connections. I have measured this while ‘playing’ in the shop and detected as much as a 9-volt drop.”

The Dometic home study course book specifically points the importance of a good neutral connection and not grounding it through the chassis, Motley noted. The manual also states all connections must be clean and tight.

“This is very important because a loose connection can produce too much heat which can create a fire,” he said.

Technicians looking into situations like this should investigate whether the refrigerator’s heating element was the correct size for that specific model and ensure that the output on the RV’s converter is showing the proper levels, Motley said.

“There are many variables that could cause the problem in this situation that are outside of the control of Dometic,” he explained. “I have never heard of this happening before.”

UPDATE: READ DOMETIC’S RESPONSE.

Article courtesy of RV Daily Report, the most comprehensive online RV industry news source.

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John Connaughton
4 years ago

Where is this board on most Dometic Refrigerators? Mine is a Norcold (I think different company), but I would like to inspect it for signs of overheating.

Joe Schmidt
4 years ago

Google “RV residential refrigerators” and you will find out very quickly that they are far superior to absorption refrigerators of any brand. We switched to a residential refrigerator. We would never go back again. They have more space, are cheaper, get cooler faster, get cooler more, frost is no longer a problem, nor is keveling a problem. Major RV brands are now beginning to offer a choice between residential and absorption refrigerators because they apparently have learned the same thing.

Sam
4 years ago

If I use my circuit tester on the 30amp side of the 110 adaptor, won’t I be provided assurance that the ground, nuteral and hot side are where they should be. And if so, will I be safe from this fire hazard?

Charlotte
4 years ago

Anytime we would plug our RV into 110 we turned everything on gas that would work on gas – mainly frig and hot water tank. Never would I consider running an a/c when plugged into 110.

It never ceases to amaze me the lack of thinking some RVers use. Like when you only have 30 amp and try to run both a/c – dumb.

Dan Cook
4 years ago

I don’t quite understand. As written it seems to be two or 3 separate subjects.

What is the burnt component on the circuit board? Did it flash over? Why would the neutral current seek a new path via ground and through the refer?

Michael
4 years ago
Reply to  Dan Cook

A/C (alternating current, NOT air conditioners per se) typically employ full wave rectifiers to convert the a/c to direct current that’s usable for electronic circuits. Engineers correctly assume the “hot voltage” is referenced to the a/c NEUTRAL conductor, not the GROUND lead (which is principally designed to protect from shocking hazards). So if the voltage source is incorrectly wired such that the current return path is through the ground connection rather than the neutral lead, the current path does not necessarily go though an adequate current path to handle the amperage and not even conduct electricity through protection fuses, etc. As an aside, these types of miswiring snafus can really screw up communications and computer circuits (as I’ve witnessed in telephony and minicomputer configurations over the years). This may be a bit advanced but provide an appreciation:
https://electronics.stackexchange.com/questions/76070/bridge-rectifier-destroyed-at-power-up

J Rodrigues
8 months ago
Reply to  Dan Cook

Two problems: the user overloaded a 15A outlet receptacle and the circuit board wasn’t designed properly.

Excessive current caused voltage drop in the 15A branch circuit. Drop causes the voltage of the line and the neutral to be pulled closer to each other. Whichever side of the circuit is weaker will experience a larger deviation from its ideal voltage. I believe the (overloaded) 15A plug-in connection failed first. It could have failed on the hot-line, the neutral, or both. Because the neutral pin failed worse than the hot, the neutral voltage inside the RV deviated away from 0V (relative to ground) towards the line voltage, perhaps by more than 20V. Circuit breakers won’t trip because a damaged connection passes less current than it should, not more.

Even though the ideal neutral voltage is 0V, appliances must be designed to give the neutral the same 125V insulation as the hot. Either a neutral-open accident like this one will happen, or someone somewhere will reverse the polarity. But the circuit board wasn’t capable of surviving neutral-ground voltage. At some point where the two conductors were too close it began to char. Once some current can flow through the charred neutral-ground path, it starts to produce more heat and more charring.

A GFCI will trip at this point. It compares the hot and neutral currents and notices that some current is missing. A regular fuse or circuit breaker won’t trip unless the circuit board chars enough to also short-circuit the hot. This is one of the strengths and weaknesses of having a neutral wire – circuit breakers do not monitor or disconnect it.

Again, the refrigerator was not properly designed. Almost all electric-powered equipment must treat the neutral and hot as equally live, dangerous, and needing insulation. (This is especially true because many common European plugs are reversible.) The only reason why US polarized plugs are common is that we allow screw-in lightbulbs. (seriously!). eetimes has a good article on exactly this subject, “The Myth of the Neutral Wire”

p.s. This sequence of events can happen even if the refrigerator isn’t running. Suppose the overload comes from the air conditioner. Once the neutral current damages the plug and creates an elevated neutral voltage, that voltage stresses the insulation of every other appliance that’s connected to neutral and ground – even ones which are switched off at the breaker. This is why neutral-ground insulation is important and one reason why neutral and ground must be connected at one and only one location.