12V Ground

[Dav5942]

Had a mental lapse(BF)! Is the 12V house ground isolated from both the AC ground and the chassis ground or are they all tied together? Trying to find a 12V house ground and am finding no ohm difference between the three grounds.

[Dav5942]

Had a mental lapse(BF)! Is the 12V house ground isolated from both the AC ground and the chassis ground or are they all tied together? Trying to find a 12V house ground and am finding no ohm difference between the three grounds.

[GaryKD]

Hi Dave,
I have no book knowledge as to what is supose to be the answer. My coach may be different than yours. While my readings are the same as yours, if I attach an aftermarket device to say the coach 12V source of power, I had better ground to the coach batteries (not the chassis or 120V grounds). Not being a EE, I don't know why this is, but it has given me fits of frustration before I was told that was wrong.

What I did was run a ground wire from a known source for the chassis and one for the coach 12V power sources. Now when I add a new device, I know I will have the correct ground.

[Dav5942]

Gary, Not sure if maybe the chassis ground is isolated from the house 12V ground?

[TheRVGuy]

Dave,

They are all the same.

This is one of the things that makes the pedestal power quality so important. In the event of a hot ground, one can have a "hot skin" condition due to the chassis being energized and when you touch something associated with the chassis, i.e. steps and the hand rail, you can get a 120VAC charge.

Hope this helps some.
Mike

[Dav5942]

Mike, thanks, what threw me off was seeing all the separate ground leads isolated on the 12v house panel. But could not measure any difference in potential.
I've got a trailor at Hog Valley that gives you the hot skin condition but haven't figured it out as the pedistal is good to go! Dave

["007"]

Ground is ground the world around , they say.
Mike has it right you will have battery ground to frame of chassis and #6 wire to frame of chassis at different locations and green wire grounds to chassis by way of third prong pins of power cords. Some times you could get a tingle thru fingers if one of these grounds are faulty.

[Dav5942]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by "007":
Ground is ground the world around , they say.
</div></BLOCKQUOTE>

Except in classified telephone systems. Remember putting in telephone systems for the NSA where the 48v ground was isolated from all other grounds-minimized the ability to overhear conversations.

[BryanL]

do keep in mind that the AC neutral is not the same as the AC ground. The AC ground should carry no currents (GFI detects any of these and throws the circuit breaker if they exist). The AC ground and neutral are only connected together at a service entrance which should also, at that point, have a good earth ground. The AC neutral and ground in your RV should not be connected together.

12v systems tend to use the ground as a return wire for the negative lead to the battery. That may save wiring costs but can be a common source of problems at times as you can't always depend upon the ground return path having good connections.