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Old 08-07-2012, 06:39 AM   #1
Capt W
 
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12 volt electrical fire

Our latest Airstream Adventure was not pleasant. My wife was using the 12 volt vacuum cleaner in preparation for our weekend getaway while I was in the house packing a few last minute items. She came into the house complaining that the plug had overheated and melted the plastic. Fortunately, I investigated immediately. The outlet was very hot and a small amount of smoke was coming from it. I grabbed a bunch of paper towels, soaked them with water then quickly removed the screws holding the outlet in place. As soon as I removed the first screw, yellow flames leapt from the wall. I raced to the main switch, killed the juice to the AS and returned to the outlet and put the fire out with the wet paper towels.

I cut and capped the wires so that I could turn the power back on. When I examined the fuse I was surprised to find it had not blown. The labels in the fuse box indicate that a 20A fuse should be used, and that is what was installed.

Clearly the wires installed on the 12 volt receptacle are undersized. They appear to be about 16 gauge when they should be 12 gauge. That is why the fuse did not blow.

I called Airstream and left a message with the service department but have not received a call back. I have also filed a report with the NHTSA. I believe this is a serious safety issue.

Here is the link to a picture of the wires. Notice the much larger wires used to supply power to the smaller ones that were installed on the receptacle.

https://www.facebook.com/photo.php?f...type=1&theater
The AS is a 2007 28' International.
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Old 08-07-2012, 06:49 AM   #2
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Sorry for you problem,

but:

"I have also filed a report with the NHTSA."

Really, without even talking to Airstream first. Sort of jumping the gun in my opinion.
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Old 08-07-2012, 06:57 AM   #3
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,i'm glad you posted this! just this past weekend while correcting a problem with my rear television connection, i noticed the same wiring issue. i believe you are correct that this condition warrants at the least an advisory notice to the owners of all involved units. this is very inconsistent with all of the other wiring i have observed in my trailer.
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Old 08-07-2012, 07:11 AM   #4
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Quote:
Originally Posted by AWCHIEF View Post
Sorry for you problem,

but:

"I have also filed a report with the NHTSA."

Really, without even talking to Airstream first. Sort of jumping the gun in my opinion.
I would agree, except that we are talking about a life or death situation. I have seen an RV fire, it is a scary sight. I have to admit, I was annoyed that I did not receive a call from Airstream yesterday after leaving a detailed message about the incident. Also, others who have read my post on FB Airstream Adventures confirmed they too had the same wiring problem.

I am sure that this situation warrants a recall and that Airstream should step up to the plate and correct the condition. I have full faith and confidence that the company will do so.

I checked the vacuum cleaner, it is rated at 85 - 90 watts. That would be 7.5 amps. My wife was using a 12 volt extension cord, this could have increased the current draw by about 15 - 20% making the current in the circuit as much as 9 amps. Not enough to blow the fuse, but plenty to cause 16 gauge wire to overheat.
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Old 08-07-2012, 07:23 AM   #5
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The RVIA standards are very clear about fusing and wire gauge, and Thor (aka Airstream) is a member of said RVIA and should have known and followed these standards!

Using 16AWG wire is fine, as long as it is properly fused at 10 amps, as the purpose of any fuse is TO PROTECT THE WIRE. 20 amp fusing indicates 12AWG wire. THERE IS NO EXCUSE FOR MISTAKES (or oversights) LIKE THIS WHEN THE GUIDELINES ARE CLEAR, PUTTING OWNERS' SAFETY AT RISK!
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Old 08-07-2012, 08:04 AM   #6
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If the 12 volt receptacle is pre wired with 16 gage wire. That wire is too small for a 20 amp load. You should check the size if the wire that A$ installed. There are 12volt receptacles that are direct wire devices. Be sure to check the current rating of the receptacle, then fuse it properly according to the wire size as long as the receptacle is rated for at least that. You must fuse it for the lowest rated device. Wire or receptacle.
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Old 08-07-2012, 09:01 AM   #7
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Been there also. Settled down to bed one night with my CPAP and immediately had smoke and fire. Shut everything down and pulled out the manual at midnight and read it with a flashlight. Eventually found that one of the little wires in the 12v socket had shorted to the sharp edge of the al interior sheet and had finally burned though the wire. But the fuse did not blow. One of the problems is that there is not really enough room to install a decent 12 socket in the wall of the airstream. Another problem is that the wires Airstream used are really small. I installed a replacement from radio shack with heavier copper wires. I had to move the ground wire on the new socket and solder it to the side to get it in the Airstream wall.

So now I still have a bunch of underwired sockets and a 20 Amp fuse? Guess I need to address that somehow, but putting in all new sockets is not a easy option. Really would like to be able to run the CPAP in the back and a 12 fan in the front.
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Old 08-07-2012, 10:30 AM   #8
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Wayne

Well I'm not an electrical engineer but sometimes I play one on TV.

There are a couple of things to keep in mind here.

First of all, the problem is not, strictly speaking, wire size. The customary ampacity limits used in building wiring are extremely conservative in smaller sizes, because they have not been revised since the early 1900s when the insulation was far more heat sensitive than today's thermoplastic insulation. 20a fusing for 16 gauge is high but not unheard of in automotive applications.

Judging from the photo, the actual problem is overheating at the outlet itself or at the terminals where the wire attaches to the outlet. This is often the weak point especially where the terminal design is poor. Without seeing photos of the burned outlet it's hard to tell exactly what happened.

The cigarette lighter outlets used so often for 12 volt power are a poor choice in many ways. It's unfortunate that the automotive industry can't agree on a better standard for 12v accessory power.

A possibility to consider is to install some other connector. One alternative is to use a 240v outlet, since those are readily available, of high quality, and unusual enough that no one is likely to plug the vacuum etc into an outlet wired for 240 volts. There are other connector configurations that will work too.
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Old 08-07-2012, 10:30 AM   #9
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The big problem with low voltage wiring is that power is supplied by increased current which can lead to heating, especially when a plug is dirty or worn or loose. Goes with the territory as they say. It is easy to develop enough heat for a fire without blowing a fuse. Keeping connections clean and tight will help assure that no excess heat is developed. Vigilance is key, no set and forget it with RV's and boats.
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Old 08-07-2012, 11:14 AM   #10
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You will find a variety of 'interesting' choices in what wire sizes are spliced-in at the end of some wire-runs... 20A for those wee wires might work in ideal conditions (I don't think so myself though)... but 12v plugs are crap.

I bought a new 12v outlet like the OEM one to plug in a 12v tv... as I noted - it was crap - so I direct wired it. Probably avoided this same scenario.
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Old 08-07-2012, 12:44 PM   #11
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Insulation is there for the purpose of protecting the conductor. The current carrying capacity of the wire is based on its size and makeup. Multi strand wire is rated higher in current carrying capacity than solid wire. Contrary to popular belief the electrons flow on the outer surface of the conductors, not thru them. Stranded wire has a greater surface area, thus can handle more current than solid wire if the same gage.
The insulation on the wire is also rated for the voltage it can withstand. While it isn't relevant in 12 volt DC circuits, you will note that there is a voltage rating on the insulation of most good quality wire.
As stated above, these 12 volt sockets are a poor excuse for a convenience outlet. Many do not make good contact. Without good contact, arcing will occur. Arcing= heat. Exceeding the current carrying capacity of a wire will cause it to turn into a heating element. Eventually the insulation will break down and may begin to smolder.
Luckily enough there are few combustibles in the wall of an A$.
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Old 08-07-2012, 01:36 PM   #12
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Does this make a case for an inverter and forget about using the 12V receptacles?
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Old 08-07-2012, 01:52 PM   #13
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Inverters have their own set of hazards. Besides heavy 12-volt DC supply cables, one adds the possibility of electrocution.

Most people don't think 12-volt circuits are very dangerous (unless they have seen a wire glowing like a cigarette lighter heating element). However, it takes very little current at 110-volts AC to stop your heart and kill you.

With a large inverter, one minute you are handling battery cables that might give you a healthy spark; and the next you are handling bare wiring similar to what's in your home. Plus, the color codes and safety requirements are different.

That black ground wire on the 12-VDC side that you were handling on the back of the inverter is not the same potential as the one coming out the 110-VAC on the other end of the box. The smaller gauge black wire on the AC side is the hot line; and you won't only get some sparks off of it, but a good 110-volt shock that can kill you.

Consequently, if you are unfamiliar with both AC and DC safety requirements, it might be advisable to have a professional help you with your wiring projects.
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Old 08-07-2012, 03:18 PM   #14
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I guess the bottom line here is that the 16 gauge wire was subjected to an excessive load that caused it to burn and the fuse used to protect the circuit was too large to prevent the overheating.
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Old 08-07-2012, 03:48 PM   #15
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Quote:
Originally Posted by Excella CM View Post
The big problem with low voltage wiring is that power is supplied by increased current which can lead to heating, especially when a plug is dirty or worn or loose. Goes with the territory as they say. It is easy to develop enough heat for a fire without blowing a fuse. Keeping connections clean and tight will help assure that no excess heat is developed. Vigilance is key, no set and forget it with RV's and boats.
Not necessarily. 20 amps flowing in a 12v DC circuit has the same heating potential as 20 amps flowing in a 120v AC circuit. In both cases, proper wiring practices and quality components are necessary to prevent fires.


Quote:
Originally Posted by Friday View Post
You will find a variety of 'interesting' choices in what wire sizes are spliced-in at the end of some wire-runs... 20A for those wee wires might work in ideal conditions (I don't think so myself though)... but 12v plugs are crap.
It's a stretch at 20a but the point at hand was that the OP's failure was not caused by exceeding the current carrying capacity of the wire.

Quote:
Originally Posted by TG Twinkie View Post
Insulation is there for the purpose of protecting the conductor. The current carrying capacity of the wire is based on its size and makeup. Multi strand wire is rated higher in current carrying capacity than solid wire. Contrary to popular belief the electrons flow on the outer surface of the conductors, not thru them. Stranded wire has a greater surface area, thus can handle more current than solid wire if the same gage.
It's this sort of misinformation that makes me want to avoid any sort of electrical thread entirely. While the electron flow does occur primarily on the surface of the conductor at radio frequencies, in DC circuits, it is diffused throughout the conductor. The differences in ampacity between solid and stranded conductors is negligible in the wire sizes typically used in 12 volt circuits.

Quote:
Originally Posted by Getahobby View Post
Does this make a case for an inverter and forget about using the 12V receptacles?
No, it makes the case for proper wiring techniques and safe components. It's just as easy to screw up 120v wiring as 12v wiring.

Quote:
Originally Posted by Phoenix View Post
Inverters have their own set of hazards. Besides heavy 12-volt DC supply cables, one adds the possibility of electrocution.

Most people don't think 12-volt circuits are very dangerous (unless they have seen a wire glowing like a cigarette lighter heating element). However, it takes very little current at 110-volts AC to stop your heart and kill you.
With the widespread use of GFCIs at this point there are more fatalities from fires of electrical origin than from electrocution resulting from 120v residential circuits.

Quote:
Consequently, if you are unfamiliar with both AC and DC safety requirements, it might be advisable to have a professional help you with your wiring projects.
There's some advice we can all take fully on board.

Quote:
Originally Posted by wrochdvm View Post
I guess the bottom line here is that the 16 gauge wire was subjected to an excessive load that caused it to burn and the fuse used to protect the circuit was too large to prevent the overheating.
Wrong. If you're going to post and ask questions, pay attention to the answers. The socket burned because it was crap. There's nothing to suggest that a smaller fuse would have saved it. Overcurrent devices, even when correctly applied, do not make up for poor materials and workmanship. Did you measure the current that your vacuum draws? How much was it? Should the fuse have blown?
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Old 08-07-2012, 04:18 PM   #16
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Jammer! It's not misinformation. 12 volts at 20 amps is 240 watts of power or heat capability. 120 volts at 20 amps is 2400 watts of heat capability. A big difference. Now that is misinformation to say they both produce the same amount of heat.
It has nothing to do with radio frequencies. If the wire overheated, it was due to bad connections or excessive load.
I won't get into the True power verses Apparent power.
I am an electrical engineer and I didn't play one on TV.
I wasn't the socket that burned it was the small wire that came with it. They call them pigtails.
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Old 08-07-2012, 07:51 PM   #17
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I had an '84 VW Vanagon that had a fire in the dashboard. Some quick thinking to pull over and disconnect the battery saved the van from burning to the ground.

Ends up a power wire in the dash was rubbing on a bracket and lost its insulation and shorted. The fuse wasn't customary at all. Some crazed engineer put the fuses downstream of the switches in the dash. The fuse was just before the lights/radio/etc. Most of the wiring was completely unfused. Very scary. Don't think that wiring design should have been sold in any market.
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Old 08-07-2012, 08:32 PM   #18
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I found a number of places where the yellow 120VAC wire that Airstream used in my trailer is running through holes in the aluminum interior shell with no grommet or protection. In one place the wire was cut to the conductor next to the shell... it looked like maybe from a knife when the lino was being trimmed...

I'll take an outlet smoking itself out over a 120VAC energized shell anytime...
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Old 08-07-2012, 08:50 PM   #19
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Quote:
Originally Posted by TG Twinkie View Post
120 volts at 20 amps is 2400 watts of heat capability.
While 120VAC x 20 amps AC has instantaneous peak power of 2400; that isn't wattage. Wattage is power over time, so you have to take RMS of current and voltage to get watts in AC. Is "heat capability" peak power? Why is that significant? I thought power over time was what circuit designs were based.
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Old 08-07-2012, 09:14 PM   #20
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Power over time is what I was referring to with the term "Apparent Power" which takes into account the RMS value. You are correct in that 20 x 120 AC will not produce a true 2400 watts of power but it will produce significantly more than 20 x 12 volts DC. When you compare it to pure DC power such as that provided by ten 12 volt batteries wired in series. The DC source would provide about 30% more heat.
In either case if the current exceeds the capacity of the wire. Bad things happen. As seen with the OP's post.
I doubt that even the socket in his trailer was rated for the 8 amps the vacuum cleaner required. So if the wires hadn't melted, the socket may have been next. There is a difference between these 12 volt receptacles and a cigarette lighter receptacle in that the latter is designed for higher current and obviously higher heat.
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