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Old 06-16-2018, 06:04 PM   #1
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Grounding

It seems from the wiring diagrams for the '17 FC FB that both the 12v and 120v electrical systems use the frame (skin, metal piping) for grounding. Can that be? I need a ground for a lighted switch install for the hot water heater. I can't stand not knowing at a glance that it is on or off. Where do I get a suitable ground?
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Old 06-16-2018, 07:06 PM   #2
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Frame or skin will work fine for a ground
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Old 06-16-2018, 07:25 PM   #3
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Originally Posted by QC TORPEDO View Post
It seems from the wiring diagrams for the '17 FC FB that both the 12v and 120v electrical systems use the frame (skin, metal piping) for grounding. Can that be? I need a ground for a lighted switch install for the hot water heater. I can't stand not knowing at a glance that it is on or off. Where do I get a suitable ground?
Not sure where else it would be possible to ground it, other than the metal skin or metal frame.
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Old 06-18-2018, 10:29 AM   #4
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Hi

Ok, let's back up a bit. Ground is a protective feature on an AC circuit. Neutral is the power return. On a 12V circuit things can get a bit confused with both protection and return referred to as ground. Protection for *both* should be the chassis of the trailer. It's the thing you are most likely to come in contact with.

If you take a look at a lot of the 12V wiring on a typical AS, they do indeed run red and black for the 12V wiring (to be confusing they also run other colors as well for low current). 12V is bonded to chassis at a couple of locations. 120V normally gets bonded at a single point.

So, 12V is very much like an automobile, with the chassis used a bit less for power return. With most of the trailer made of aluminum, tying things in without corrosion issues is a bit problematic. That drives a lot of the differences.120V. is similar to your house.

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Old 06-21-2018, 05:30 PM   #5
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I like the idea of a LIGHT on the H2O heater!
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Old 06-21-2018, 06:29 PM   #6
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All of the 12 volt circuits on my Airstream are 2 wire circuits. I have not seen anything grounded to the chassis as part of the power source. But I guess you could do it to the chassis. I wanted a light on the wh at first but have come to accept the way it works without it now.
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Old 06-22-2018, 06:45 AM   #7
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Hi

There are a couple points where they tag to the chassis on my trailer to run it in parallel with a return wire. The jack on the front returns through the frame. I suspect that the power stabilizer jacks do the same thing.

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Old 06-22-2018, 07:42 AM   #8
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Quote:
Originally Posted by QC TORPEDO View Post
It seems from the wiring diagrams for the '17 FC FB that both the 12v and 120v electrical systems use the frame (skin, metal piping) for grounding. Can that be? I need a ground for a lighted switch install for the hot water heater. I can't stand not knowing at a glance that it is on or off. Where do I get a suitable ground?
Your switch can be connected to the trailer skin or frame, to provide a negative path.

People confuse the terms negative and ground. (I am guilty of using the wrong term too)

There is no ground in a 12 volt DC circuit, there is only positive and negative. In our trailers DC positive comes from either the battery's positive or the converter's positive. The negative from both the battery and converter are connected to the trailer's structural metal. So anywhere structural metal is connected continuously it is negative.

There is a ground only in the 120 volt AC system, at times, but not all of the time. There is only a ground if/when the ground wires are connected to the earth. When plugged into shore power there is an earth ground through the ground wires. When plugged into a generator there is no ground, unless the generator is grounded or the trailer in contact with the earth provides ground. (tongue jack, stabilizer jack, plumbing/water, cable TV, etc may provide a path to ground)

The ground wires in the trailer's 120 volt AC system and the negative in the 12 volt DC system just happen to be connected through the trailer's structure, but are not dependent on one another.
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Old 06-22-2018, 09:13 AM   #9
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No indicator light bugged me too. Plus I was always turning it on instead of the light since the switches were the same. Replaced mine a couple of weeks ago.


Check the wiring diagram in the manual for your water heater. On mine the negative for the red fault light ties directly to the battery negative, so I used that for my negative connection on the on/off indicator.
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Old 06-22-2018, 12:28 PM   #10
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The light on the water heater was pretty easy. I got the lighted switch at an RV supply store. It is rated for 14 - 125v. I replaced the existing switch only. The existing wires go to two points on the new switch as shown on the switch package. The third lug on the switch is for a ground. I picked up a ground from the indicator light on the propane side of the panel. Works great, and now I know.
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