Grounding

No solar. 15 amp shore or generator to run Genius2 which charges battery(s). Should shore connection be grounded to frame? Should inverter be grounded to frame? Should leisure battery be grounded to frame? When shore available, separate outlets available to run TV etc. If grounded to frame it would be only connection to DC system.

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  • BB.BB. Super Moderators, Administrators Posts: 29,500 admin
    Welcome to the forum SB...

    Grounding is one of the most complex questions out there. And and RV with multiple AC and DC power sources makes it even more complex.

    In general, it is normal to ground the DC Battery Negative Bus to the RV frame. If there is a short circuit from hot (+) to ground, it should pop the fuse/breaker protecting that wire--Rather than making that metal "thing" not.

    In RVs, you may have the metal frame, sheet metal siding, plumbing, electrical boxes, etc... And the grounding among all that stuff being "iffy" (many RVs use plastics and wood studs which support and insulate metal items).

    Assuming you are in the USA (New York?), 120/240 VAC power has the neutral ground bonded to the earth/green wire (in a home, it is usually done in the main breaker/fuse panel for the home). This is done for safety. Both the white and green wires are always at zero volts (ground potential), as well as plumbing, natural gas, many appliances (generally, metal appliances are grounded to the green wire through a 3-prong plug). The idea is that if the Hot wire (Black or Red typically) gets exposed and shorted to metal (like a plumbing pipe or sink), the green wire will short circuit the AC output and trip the breaker--And turn everything off (on that branch circuit).

    With an RV, the AC neutral bonding is provided by the Home/RV Park. When you disconnect the external power connection, your white wire to green wire ground bond is "gone".

    In larger RVs and those more complex power systems, typically, the RV will do the Neutral to Green Wire bonding inside the RV. Typically at the Genset and/or AC inverter. (and the green to white wire bonding is lifted by a relay when shore power is connected).

    This is complicated, and depends on the exact hardware (genset, AC inverter, size of devices, etc.) to know what to do. Typically, from what I have seen, gensets and AC inverters larger than ~3,000 or 3,500 Watts have the green wire and white wire "bonded" internally to the device (I am not an expert, just what I have seen). You can setup relays that will do the auto-bonding/bond lifting as needed.

    Now, back to reality... If you have both a white/green wire bond at the shore power source, and a white/green wire bond "active" in the RV, it will typically trip the ground fault breaker at the shore power outlet--Hence the reason to not do both at the same time (shore power bond + RV bond).

    Other than for safety (very important), there are usually very few reasons why AC ground bonding is done (fluorescent tube fixtures start better/more reliably, spark ignition for gas appliances works, etc.).

    So, assuming none of the above two reason apply to you (neutral/ground bonding of AC power inside the RV), another solution (for safety) is to use ground fault outlets--Especially on the exterior AC outlets, and near the kitchen/bathroom sink. The GFI will trip if there is a short (or person grabbing a "hot wire") and shut of the AC power to that outlet.

    You could, for example, put an GFI on the main output of your AC inverter--But if that tripped, you would lose 100% of your AC power (example, your mixer falls in sink, and your overhead lights go out on a dark night)... So, I suggest that GFI be broken up so that if a power tool trips the GFI, the other circuit(s) are still powered.

    If you have GFI outlets to your exterior outlets (and interior near water outlets), then you really do not "care" what is providing your AC power (shore power, genst, AC inverter in RV)--You are safe. And you can use separate AC outlets for Shore vs AC inverter power, or you can use some sort of relay/shore power transfer switch to power an outlet from either AC inverter or shore power--It is really your choice.

    There is another issue with grounding... You mentioned TV, but HAM radio and folks that listen to AM radio find--Grounding or not of DC/AC power can affect receiver performance. And even things like LED/CFL lighting vs standard filament can be the difference between between a TV receiving signals or not. Generally, ground bonding is not a big factor in RF interference, but it can be a factor in what solutions are used.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sandebagger2usandebagger2u Registered Users Posts: 2
    Bill, Thanks. Very informative. I'm trying to KISS. It's just a Chevy van. Only have 1 now, but getting another 100ah battery. Genius 2 does a good job of charging battery. So I will leave the shore or generator source unconnected to frame, the inverter connected to - battery and the additional inverter ground connected to ground bus bar. Ground - bus bar to frame. (thru shunt maybe). Not sure but can't live forever.
  • xminemanxmineman Registered Users Posts: 5
    I have been using an UN-GROUNDED system for 5 years now with no ill effect. My RV's 120 vac electrical system keeps the neutral isolated from the ground, as the neutral to ground bond is provided at the Pedestal plug in. As per NEC a system should be grounded at only one point. Do not confuse bonding with grounding.  My solar panel frames are bonded to the ground at the common ground point at the rv's ground terminal, as are grounds for CC and dc breaker panels. Bonding prevents a difference of potential (voltage). When off grid it is a floating system as there is no potential to ground for current to travel. When plugged in on grid they are bonded to ground via shore power connection. 
    Most of Europe runs un grounded with no problems. I run extensive electronics, all un-grounded, with the exception of antennas and router which require a physical ground. Multiple grounding points can cause ground loops which can interfere with electronics. As an added level of comfort for myself, I have installed a battery selector switch between the RV's 12 volt panel and the rv's batteries up front and large solar batteries creating 2 distinct 12 vdc power sources. This allows me to keep my expensive solar batteries away from the rv's Dc converter  for the rare time that I am on grid. I also allows me to isolate the tow vehicle electrical system and RV's electric over hydraulic disc brakes from solar electrical system. When on grid I have the ability to run my workstation off of the solar via inverter, as that is by far the cleanest power. As my inverter is floating no possibility of a difference in potential between systems.
    1987 Avion 9.1 Metre with 5 Kyocera 270 watt panels, Midnite Classic 150 mppt controller, Approx 14.4 KW provided by 6 in series Fullriver dc1150-2 2 volt agm cells, Exeltech 2Kw pure sine inverter, Battery transfer switch to isolate pesky converter from solar components, 120 amp battery to battery charger to allow dc back up from tow vehicle and 2 Honda 2000 generators for the very rare need to back up. Networked with Cradle point AER2100 router ATT/ Verizon, WiFi as WAN on Exeltech 125 watt inverter. Microwave, 2 induction cook tops, Mr. Coffee and a pretty nice toaster.
  • EstragonEstragon Registered Users Posts: 3,957 ✭✭✭✭✭
    Grounding and bonding gets really complicated in mobile applications.  What happens, for example, when shore power polarity is reversed (apparent "hot" is bonded, "neutral" is at 120v potential to ground)?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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