Bonding solar system to chassis when house system uses chassis as return path

[dpasch80]

I have a travel trailer which uses FLA as the standard house system and the return path of that system is through the trailer chassis. I also have an independent lithium solar system with the return path directly back to the battery. The two are only connected in that I have a DC2DC charger from the solar system to the house system.

I am now thinking about grounding the solar system by running ground wires from the equipment (inverter, etc.) to negative bus and then to chassis as well as a ground wire from the panels to the chassis.

What I don't understand is whether bonding the system and panels to the chassis for fault protection has any unintended consequences when that chassis is also the return path for the house system. For example, what happens if there is a fault in the solar system and over current is routed to the chassis...does that go into the house batteries?

(also, anyone have recommendations for a ground lug for the panels which are attached to superstrut using z brackets? The things I find on amazon assume a different rail system and superstrut fittings don't assume panels.)

Thanks

 

[HRTKD]

There are a lot of RV/PV installs where the panels are not grounded to the chassis. The OEM install on the trailer next to mine at the storage lot does not. I hesitate to say that just because most RV/PV installs don't that you don't have to either. There's no way to get the PV to an actual earth ground unless you drive a grounding rod into the ground or you are connected to shore power.

 

[mikefitz]

The terms ground and earth when it involves mobile systems is the metal body and chassis, not the dirt outside.
By bonding battery negative, inverter casing, AC protective earth conductor, to the body/chassis/'ground' you are forming a return path so that fault conditions cause protective devices, fuses and breakers to trip.
Where this path does not exist there is an increased risk of excess current via a fault causing fire or with AC circuits the additional risk of electrical shock.
Nothing can 'get into' the house battery unless it has access to both the positive and negative terminals of the battery.
Most RV solar systems, unless there are more than two strings, cannot generate enough current to trip a fuse or breaker in the feed path, ( unless hit by lightning). A shorted solar panel generates current with zero volts, thus no power.
I can see some advantage in connecting the frames of solar panels to the vehicle ' ground' so a static or inducd voltage cannot build up.

Mike

 

[12VoltInstalls]

can see some advantage in connecting the frames of solar panels to the vehicle ' ground' so a static or inducd voltage cannot build up.

Agreed. I might ground the frames with a separate wire to the frame and not to the busbar that serves everything else because I’m funny like that.

that’s just one of my quirks- electrical connections and equipment cases get joined, ‘static’ wire isn’t part of the electrical system so I’d use a separate wire. I don’t think there’s any rules anywhere that require that though.

 

[dpasch80]

Thanks for the replies. I'm still mentally stuck on bonding one system from neg bus to the chassis which another system uses as its return path, thus effectively having their negative paths cross.

Nothing can 'get into' the house battery unless it has access to both the positive and negative terminals of the battery.

So forget grounding for a second. In the mythical setup below where two systems would share a negative but their positives are unconnected those system would still be independent? Nothing bad could come of it?

 

[Zil]

Nothing bad has ever come of my systems. I build circuits for RV's, Boats, Vans, and Food Wagons. I have battery negatives, all battery negatives, to negative BusBars. Negative BusBar to chassis. DC device case lugs to chassis or BusBar. High use devices as chargers, inverters, fuse blocks and such each have a negative return cable to the BusBar. I only use chassis dc returns for lights and small fans. Maybe radio. The external ac voltage supply has a green "earth" wire. It is connected to the chassis. Basically, the chassis becomes the negative reference for the whole of all the systems.
Some boats I have worked have 5 separate battery banks. The negatives all connect to a common negative, usually the engines.

 

[12VoltInstalls]

Nothing bad could come of it?

In practical terms?
No, nothing bad will happen.

thus effectively having their negative paths cross

They don’t. In practical terms think of EVERY part of the chassis as having THE SAME EXACT ELECTRICAL POTENTIAL LIKE A GROUND PLANE. The electrons just tumble along where they need to go.
Grounding to the chassis imho is a safety item, a static dissipater, and a means of avoiding unintended paths to ground in some unforeseen situation.
But all equipment imho should home run to the busbar not the chassis anyway.

 

[SlowPony]

There is indeed a problem that can arise from joining the House batteries and Engine Batteries in an RV situation. I don't know of any safety hazards persay, but if your vehicle uses any DC negative communication signals, such as a Ford, you are setting yourself up for trouble. In the case of the Ford E40D (E super duty cutaway) they make careful work to have the chassis ground separate from the engine ground. The speedo and transmission rely on signals sent thru the negative return from the brake light to control the transmission. It's a dumb design and we are stuck with it! If that signal is compromised it will interfere with the proper operation of the vehicle, force it into limp mode! At this point most people take it to the shop where they are sold a new transmission which continues to limp!