Isolated floating system Vs chassis grounded system

[Geo.Lander]

Hi guys! Some more advice (again)

I see the topic of chassis grounding (local earth) vs floating systems (IT) brushed over in most cases and not covered in full context and I am still not seeing a clear strategy from reading and re-reading Wiring-Unlimited.

I know the trucks existing system is chassis and engine grounded and I am trying to decide on the best route for my system in the box. A full Chassis ground and what that might imply for the existing trucks DC systems (grounding loops etc) or full floating isolated system. Another topic is AC grounding and the isolation of the shore power.

So I suppose I wanted a summary and advice around higher power AC inverters and the grounding strategy there but also what DC grounding loops (if any are they connected to your chassis?) you guys have built into your systems.


DC component chassis grounding with Ground fault circuit interrupter on the AC loads, the question for me is where does that ground end up? Should I just ground all the Victron components to the negative bus bar and leave it at that?

 

[Joe917]

Where is the shunt for the battery monitor?
I would advise a dedicated ground wire for every circuit, do not use chassis ground for the DC.
The Victron inverter installation manual should have all the grounding details.

 

[Geo.Lander]

Where is the shunt for the battery monitor?
I would advise a dedicated ground wire for every circuit, do not use chassis ground for the DC.
The Victron inverter installation manual should have all the grounding details.

That is just an example diagram from the wiring unlimited handbook Joe. I will use the Victron Lynx shunt.
What do you mean a dedicated ground wire, why would you advise that? Ground is supposed to be a common neutral return in a AC system, i am sort of asking where it should be ground and why are you advising not to ground the box/house DC system to the chassis (I will have both 24V and 12v)?

 

[Joe917]

Run a return ground wire on every DC circuit (to battery negative busbar), this will ensure a good ground and make future trouble shooting easier . There is no reason to ground the DC circuits to the chassis.
The inverter will require a chassis ground, you should get the advice of a qualified electrician for the AC circuits and grounding.
Make sure the shunt is the only connection to the battery negative.

 

[Iain_U1250]

Not so sure about 110V systems and GFCIs, but here in Australia, there is a problem with inverters and that my truck was not connected to any true "Ground". This meant that even if I had an RCD, it would not trip if the neutral came into contact with the chassis, and as you go to get in the truck, you become the ground. Some clever guys came up with this device, a RVD-EI, which when combined with the RCD, will trip out if the inverter power comes into contact with the chassis, which a normal RCD won't do. RVD-EI

 

[Alloy]

Here's good place to learn

RV Electricity – Making the RV world safer, one campground at a time.

rvelectricity.com

 

[charlieaarons]

As far as DC: my 2 Sterling battery to battery 12-12 45-50a chargers have 3 posts: +12v to camper batteries; second +12v to chassis batteries; and ONE ground post. For both chassis and camper. So clearly the camper and chassis have a common ground.
The inverter draws DC (up to 300a) from the camper batteries and obviously has to have DC ground to camper batteries.
Any possible connection of AC neutral or ground to camper DC battery ground would occur internally in the inverter. I think. I will check wiring diagrams and let you know if not completely correct.

 

[Geo.Lander]

On singlephase AC systems, ’Live and Neutral” carry load current. Ground is not supposed to carry any current except during a fault condition.
There is abundant further accurate info online. Far in excess of what I will take time for here.

Exactly, whereas DC chassis ground is sometimes used as a circuit. i understand the common traits and diagrams concerning earth to "shore" if plugged in and a floating system as far as AC is concerned from the inverter when using RCD wired devices. I just cannot work out the best approach to wiring in combination with DC grounding (both 12v and 24v). I do understand the DC loads will in effect be isolated (that is the nature of DC) but what kind of situations can occur if I use the chassis to ground 12v, 24v, 24v truck system?

 

[Iain_U1250]

Exactly, whereas DC chassis ground is sometimes used as a circuit. i understand the common traits and diagrams concerning earth to "shore" if plugged in and a floating system as far as AC is concerned from the inverter when using RCD wired devices. I just cannot work out the best approach to wiring in combination with DC grounding (both 12v and 24v). I do understand the DC loads will in effect be isolated (that is the nature of DC) but what kind of situations can occur if I use the chassis to ground 12v, 24v, 24v truck system?

I've wired my "-" for each of the batteries to the chassis (via the shunts for the two battery monitor) to a ground point on the cab chassis. My inverter "-" is attached to the chassis frame of the camper box, which in turn is grounded to the truck chassis, all with 70mm2 cable on a tapped hole at each point. My shore power comes in to the 30A battery charger, rather than run a seperate circuit, and all 240V power comes from the inverter. I've had no problems with grounding the chassis, the camper box chassis, engine and the cab at separate locations. As long as you have decent heavy duty cables, and that the ground point is either a welded stud or tapped hole, , not just a hole and some bare metal, I think you should be OK. The chassis on the camper is normally independent of the truck chassis, mine is rubber mounted so hence the need for a proper ground cable, same goes for the truck cab, engine, transmission etc. Best to put in decent amount of ground cabling, preferably to a common point, rather than let the current find it's own way through various connections.

 

[Alloy]

With heavy loads and/or long runs using the chassis or a ground strip (in a box) will save $$ in both the size and amount of wire used.

Over the years even I found a gound on each 110v device and each battery bank works best.