Grounding

[QC TORPEDO]

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?

[GMFL]

Frame or skin will work fine for a ground

[overlander63]

Originally Posted by QC TORPEDO

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.

[uncle_bob]

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.

Bob

[mythbuster88]

I like the idea of a LIGHT on the H2O heater!

[Bill M.]

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.

[uncle_bob]

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.

Bob

[A W Warn]

Originally Posted by QC TORPEDO

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.

[kenen42]

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.

[QC TORPEDO]

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.

[shannon]

So what I would like to see is the hardware used to ground to the frame or skin. I am also wondering why not ground both solidly? I am talking in terms of 125V. of course.

[A W Warn]

Originally Posted by shannon

So what I would like to see is the hardware used to ground to the frame or skin. I am also wondering why not ground both solidly? I am talking in terms of 125V. of course.

"Ground" (a connection to earth) goes from the breaker panel/box through the power cord and is actually grounded to earth wherever it exists in the power supply system. The grounding wire of the 120 volt system is connected inside the electrical panel to the ground bar which is connected to the panel box. There is a copper wire that is connected from a ground lug inside the box that goes to the trailer frame and is connected with a bonding clamp.

What people sometimes are confused by is the "negative" of the 12 volt system is connected and in common with the 120 volt ground.

[uncle_bob]

Originally Posted by shannon

So what I would like to see is the hardware used to ground to the frame or skin. I am also wondering why not ground both solidly? I am talking in terms of 125V. of course.

Hi

If you tear out the AC power panel in your RV, you will find a bare wire. One end is tied to the same buss bar as all those bare wires from the AC distribution wiring. The other end heads away from it towards the frame. It likely wiggles around a bit. Eventually it goes over and gets clamped to the frame with a bolt. There are multiple ways you could do that. I'd bet that over the years, AS has used them all.

Bob

[Mollysdad]

Originally Posted by QC TORPEDO

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?

There's a ground available on the switch plate itself.
Thanks GMFL (Airstream Nuts and Bolts).
You know that light that's never on unless you have a problem? It's got a ground. Split that and send the ground to your new switch. I used a WAGO connector.
IF you have a WH that has gas or electric, split it twice.
But there's one caveat. If you're NOT on shore power and you flip the "electric" switch, the light still lights. I didn't care, I'm concerned when I leave it ON all day by mistake.

[richard5933]

Originally Posted by shannon

So what I would like to see is the hardware used to ground to the frame or skin. I am also wondering why not ground both solidly? I am talking in terms of 125V. of course.

Here's how I accomplished this - all my 120v ground conductors from devices in the front of the trailer (converter, inverter, etc.) are connected to this point on the frame. This is not the stock connection, but rather an upgrade I did.

In addition, there is another copper grounding lug bolted to the rear of the frame which is where the breaker panel and incoming shore power cord make their ground connections.

[shannon]

Thanks richard5933. I wasn't exactly after a lesson in "ground vs. negative," and that image helps! This is a ground up rebuild by me, so there's a lot of freedom ... to get it right and to make mistakes!

[richard5933]

Originally Posted by shannon

Thanks richard5933. I wasn't exactly after a lesson in "ground vs. negative," and that image helps! This is a ground up rebuild by me, so there's a lot of freedom ... to get it right and to make mistakes!

One thing I forgot to mention on my previous post...

Before mounting the grounding block, I used a flap wheel on the grinder to get the metal on the frame to bare metal, and then used conductive grease to protect it before mounting the grounding block. After all the connections were made, I liberally smeared the grease all over the bare metals before installing the plastic cover. I wanted to help protect against future corrosion as much as possible.

I like you attitude too - you will get some things right and you will make mistakes on others. All part of the process. Hopefully all our mistakes are small and recoverable.

[shannon]

OK, call me loco, but I am going to give the visual blow-by-blow of wiring this beast. First, above, is welding a G8 bolt to the chassis. That's the grounding to the frame. Power center is front and center on the '70 Safari '23.

[DaveG]

Actually I'm not a know it all I am cautiously & humbly offering my two cents just in case it may help someone who is scratching their head over the info offered so far. I read the posts and do not disagree. All has been said but if one is not really familiar with the worlds of low voltage, DC, and higher AC voltage a few may get lost. It is really fairly straight forward. In 120 volt AC circuits there are three wires. The black (or color other than unbleached cotton or white) is an "ungrounded" "current carrying conductor". The white (or unbleached cotton) is a "grounded" "current carrying conductor". The green or bare is a "fault" "current carrying conductor". That is it only carries current if something is wrong. If the grounding conductor (green or bare) gets current the intent is to cause the circuit breaker to open because you have a short somewhere. Without a good path back to the source your metal trailer may get and stay energized (hot skin), not good. All metal parts are bonded together so any contact with the ungrounded leg of the circuit will take a path back to the ground bus and hopefully back to the source of power. A 12 volt system does not electrocute humans. Voltage is the pressure and below 48 volts is generally not enough pressure to cause direct contact harm. It will make something hot enough to start a fire if not fused correctly. A 12 volt system which relies on a chassis frame may be unreliable. It may also cause corrosion. Using the frame or skin in a circuit is turning that metal into a conductor. Dissimilar metals are already sharing electrons which leads to corrosion, but when in a circuit corrosion is accelerated. Two insulated wires (a positive and a negative) for a 12 volt circuit works best.

[Mollysdad]

Originally Posted by richard5933

Here's how I accomplished this - all my 120v ground conductors from devices in the front of the trailer (converter, inverter, etc.) are connected to this point on the frame.

Just curious. Why did you run separate grounds to the external ground bar? Did you consider one larger gauge wire running inside and putting the ground bar inside?