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Old 05-28-2020, 09:31 AM   #1
beeje
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WARNING Burnt up water heater junction box

Went camping over the memorial day weekend. Upon set up (with water heater full) I turned on the 120 volt heater switch and left it on.

On sunday, I smelled something strange but could not figure out what it was. Got up Monday morning to take a shower and no hot water. Thinking maybe someone turned of the switch, I looked, its still on.

I go outside and pull the little black switch out and check for power, no power present.

I go inside and take apart the cabinet consealing the heater. Found a junction box whitch is mounted to the heater case from the outside. Just barily touched it and got a small fireworks show. To remove the cover the box has to come off.( Bad design )

I Turned off the power at the panel and removed the box and its cover and found a burnt of mess.

In the box is a 12 volt relay that switches on the 120 volt heater from the switch panel.

Unit still worked on propane so I said I would fix it when I got home.

I decided to abandon the 12 volt switch in the switch panel and hard wire it to the bathroom wall by the sink. I used a pilot lighted switch so you can tell it is on.

Had to cut a few access holes in the underbelly to do it.

Wired it so the little black switch still functions as a fail safe and must be on for the wall switch to power up the heater.

Just a guess, but I think a loose conection from heating up and cooling down over time was the cause. ( another bad design IMHO ). Tried to post pics, but cant figure out how to.

Not saying you all should tare your unit apart to look but be aware of any odd smells and act quickly before disaster happens
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Old 05-28-2020, 09:34 AM   #2
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M.O.C. #17894
new water heater switch.jpg

burnt water heater box.jpg


Figured it out. LOL
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Old 06-02-2020, 08:46 PM   #3
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No response's ?!!! I find it hard to believe that no one is concerned about a factory wired water heater that has the potential to catch fire and burn your unit to the ground with you and your family in it.
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Old 06-02-2020, 09:04 PM   #4
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I appreciate your post letting us know what you found. I think this is the first posting I have seen with this problem. Good catch. Not sure where that box is on my model. I may take down the wall in the pass-thru just to see if it may be visible from there. Looks like it took 9 years for the problem to develop. Lots of bad roads and bridges to shake that connection loose. Thanks for the heads up.
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Old 06-02-2020, 09:59 PM   #5
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Were there any wire nuts in your junction box? My unit almost burnt down do to poor craftsmanship on the wiring from my factory installed generator. Lucky thing Keystone put metal junction boxes in our units. I kept smelling burnt plastic and thought the generator was overheating, nope all the 110v wires and wire nuts melting/burning. Junction box was so hot it burnt my fingers when I touched it. Only thing left of the wire nuts was the little metal inserts.
Glad you found the problem before you had flames.

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Old 06-03-2020, 05:32 AM   #6
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Yes they were wire nuts connecting the leads from the relay to the hundred twenty volt feed to the water heater. I suspect that's where the issue was.
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Old 06-03-2020, 05:32 AM   #7
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That was supposed to say 12 volt
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Old 06-03-2020, 08:04 AM   #8
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Odd, I check the forum for new posts regularly and did not see your original post. Maybe that is why no one else commented on it.

But you are not the first to report burned wires in that J box. Has been reported several times over the years after water heater stopped working. Often it was the neutral wires that burned due to bad wire nut connection.
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Old 06-03-2020, 08:40 AM   #9
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I'm no electrician, but how do the wires in the junction box get hot enough to melt, and not trip the breaker? I'm pretty sure that is only a 15A breaker in ours, and it is the only thing on that breaker. It seems like it would take a lot of amps to actually melt things inside of there...
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Old 06-03-2020, 08:50 AM   #10
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all I know is I moved that box very slightly and got a firework show. Breaker never tripped
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Old 06-03-2020, 10:12 AM   #11
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I guess we were lucky, when our wires to the relay melted they shorted out and tripped the breaker. Same, only thing left of the wire nuts was the wire spring.
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Old 06-03-2020, 11:06 AM   #12
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Actually it can overheat to the point of melting or fire without exceeding the breaker rating. A loose wire connection causes resistance. And current flowing thru a resistance causes heat. Heat in watts is the current squared times the resistance. That’s the principle of light bulbs, get the element (resistance) so hot they glow.

Wire nut connections, done correctly, work well. But not done correctly can lead to a bad connection over time.
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Old 06-03-2020, 01:24 PM   #13
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Quote:
Originally Posted by BB_TX View Post
Actually it can overheat to the point of melting or fire without exceeding the breaker rating. A loose wire connection causes resistance. And current flowing thru a resistance causes heat. Heat in watts is the current squared times the resistance. Thatís the principle of light bulbs, get the element (resistance) so hot they glow.

Wire nut connections, done correctly, work well. But not done correctly can lead to a bad connection over time.
I agree a correctly wire nutted connection should be fine. I believe the issue is trying to wire nut together a solid and a stranded wire.
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Old 06-03-2020, 02:07 PM   #14
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Quote:
Originally Posted by beeje View Post
I agree a correctly wire nutted connection should be fine. I believe the issue is trying to wire nut together a solid and a stranded wire.
Yeah, I never like those connections either. However, that's probably not as much as issue with Keystone as it is with the heater manufacturer for using stranded on the heater side. I'm sure they do that so that it's easier to assemble FOR THEM...
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Old 06-07-2020, 02:47 PM   #15
allenclme
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I am glad you found this in time to prevent a possible fire. I have to be honest. When we are not physically inside our RV, I turn off everything on AC power except the main Air conditioner. We also close the propane tanks. Don’t do this when boondocking on 12v.
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Old 06-07-2020, 07:03 PM   #16
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Wow, glad you found it. This is a good reason to investigate any hot wire or melting plastic smell. These units bounce, bump, and flex as we travel. A properly tightened and checked wire nut should take it but that is only if it was properly connected and tightened.
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Old 06-08-2020, 05:28 AM   #17
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Guess I'll add that to my list of "too do's". I believe our HW heater is reasonably accessible after removing a panel in a cabinet.


Wire nuts have their place but I'm beginning to believe that the rolling earthquakes that are our RVs is not the right application. but should be pull apart connectors such as the tow vehicles
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Old 06-08-2020, 07:00 AM   #18
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This seems to be a rather common problem. I had the same thing on my 2017 MHC 305RL. We bought it used in 2018. When I turned on the electric water heater element I smelled burning wires. We just didn't use it. Finally got around to looking into it a few weeks ago and traced it to the junction box (plastic) where the supply 120v connected to the water heater. I could see the plastic on the junction box (not really a box - just a covering) melted. I had to twist my body and arms between drain pipes, furnace ducts, etc. to just be able to reach it. Turned out that the 120v wires were connected with wire nuts, and the hot side was the culprit. I stripped back the burned part of the wires and reconnected using crimp on connectors. That fixed it - my water heater now works on 120v. It was probably a poor connection right from the factory, but I agree that I would be very hesitant to use wire nuts in any connection because of all the vibration over time.
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