Grounding to bus chassis

[Scott & Heather]

My electrician is doing an amazing job of installing our electrical system on our coach. He's using all 12 and 14 gauge THHN wire and he's an artist in how he runs the wire...using liquid tite everywhere and rubber grommets throughout. He has done a ton of research on how to properly wire the 120 V system of an RV. He's come to the conclusion that we need to ground to the chassis. He did do this. He's also going to figure out a way to bond the generator power. Just wanted to get everyone's opinion here how they did this. We are looking at making a special plug that just plugs into the generators outlets to do this...


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[Jim Eh.]

Hey Scott,
Hope all goes well and quick with the electrical. Since TV is soooo pitiful here if you get some time, could you fix the link to your progress picture site? Gilligan is really getting old!

[niles500]

Plenty of info in the archives on neutral ground bonding and transfer switches, worth the read, remember 4 wire and only one neutral ground bond AT the source - hth

[bevans6]

You tie the electrical system ground to the chassis permanently and to the ground of any power source, be that inverter, generator or outside power.  For outside power, that is done through the power cord.  You bond neutral to ground only once at a time, at the source of the power.  Normally that means that neutral is switched on and off the same as the live lines are, as you connect to each power source.  Doing that with a plug is fine, as long as you remember to disconnect the plug if the generator is off.  I use a automatic transfer switch and leave the plug connected to the generator all the time.

Brian

[gumpy]

You said "outlets".  You probably only use one outlet, but it may be possible to use one for each leg of your 120v panel.

Yes, it's ok to make up a plug (actually receptacle) for this. You can incorporate the neutral/ground bond in the receptacle from the generator. You would also then have a similar receptacle for the shore power, and one for the inverter (also incorporating neutral/ground bond). There would be a single plug pigtail from the electrical panel that you move between the three receptacles to select your power source. This is the most simple and fool proof method of power source selection, though it does require complete disconnect of power in the bus when switching and would require you to shut off your high loads when switching, but you should do that anyway, even if you use a ATS.

The battery bank negative, A/C distribution panel, inverter and generator grounds should be bonded to the coach body at a single point. Just weld a bolt to the frame and bond them all there.  In reality, the generator will be bonded to it's frame so will be bonded to the coach where it's bolted down. Typically the same for the inverter and A/C panel.

[oltrunt]

There does seem to be a range of answers  on this topic.  Just to further muddy the waters, here is what OSHA says about grounding/bonding generators in RV's:
https://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf

If you aren't acquainted with Mike Sokol's "No Shock Zone, it is a very easy to understand explanation of all things electrical in RV's--in particular,how to prevent getting shocked.  While Mike's info can be purchased on line, it also can be viewed on several sites.  I just came up with this one:
http://rvtravel.dreamhosters.com/category/rv-living/rv-safety/no-shock-zone/.

Perhaps the single most important lesson from the article(s) is that there be only one neutral/ground bond for each electrical supply source(and why).  Hope this helps, Jack

[HB of CJ]

A 12VDC, (24VDC) chassis dedicated grounding bar running the length parallel to the main chassis boxed rail.  This bar has multiple grounding points.  All the grounding needs of the DC CHASSIS electrical system runs through this bar.

As far as the HOUSE high voltage alternating current grounding needs, perhaps somebody can tell us how it works and how it should be done.  I suppose one does not want to mix up the two, (2) separate electrical grounding systems?

[oltrunt]

HB, exactly.  Read both the above articles and the wax paper over the crystal ball will be removed!  Jack

[bevans6]

A 12VDC, (24VDC) chassis dedicated grounding bar running the length parallel to the main chassis boxed rail.  This bar has multiple grounding points.  All the grounding needs of the DC CHASSIS electrical system runs through this bar.

As far as the HOUSE high voltage alternating current grounding needs, perhaps somebody can tell us how it works and how it should be done.  I suppose one does not want to mix up the two, (2) separate electrical grounding systems?

You can keep the AC ground separate from the DC grounds for wiring purposes, you need to always keep low voltage Dc and higher voltage AC wiring separate, but the actually chassis ground connects are tied together.  You should always connect the ground of both AC and DC wiring to the chassis of the bus.  according to the OSHA article, you also should drive a ground stake if running off the generator and powering up a trailer, so that ain't going to happen.  Unless someone has a source for 60 mph ground stakes... 

[oltrunt]

The OSHA article actually says, "frame of a portable generator need not be
grounded (connected to earth) and that the
frame may serve as the ground (in place of
the earth)"----and,  (the) "frame of a portable generator need not be
grounded (connected to earth) and that the
frame may serve as the ground (in place of
the earth)."  Therefore no 60 mph ground rods needed .   
Jack

[bevans6]

The OSHA article says that (above) if the generator  supplies only equipment
mounted on the generator and/or cord and
plug-connected equipment through
receptacles mounted on the generator.

this is what would apply to a generator supplying power to a bus:

If the portable generator is providing electric
power to a structure by connection via a
transfer switch to a structure (home, office,
shop, trailer, or similar) it must be connected
to a grounding electrode system, such as a
driven ground rod. The transfer switch must
be approved for the use and installed in
accordance with the manufacturer's installation
instructions by a qualified electrician.

[Dave5Cs]

And we're off, My cat wants to watch too!...

[luvrbus]

We always had to drive a ground rod on a portable generator to comply with OSHA standards in Oklahoma maybe that has changed now with those idiots 

[gumpy]

I didn't read it. I don't really care what OSHA says.

[oltrunt]

Bevans6, I get what you are saying and I agree if the genny is sitting outside the bus on the ground.  On the other hand if the genny is a permanent install in the bus then bonding to the genny frame is the ticket.  Jack