In a rubber tyre insulated motorhome, is there any downside to attaching an earth rod to the chassis when parked up, when using 240v ac inverter power only(no grid tie or grid earthing) ?
Is it safer with the earth rod connection or not?
asked
Earth Rod attached to motorhome...any unforseen detrimental effects?
What appliances are you using outside of the vehicle to need a connection back to the supply protective earth?
What are the current earthing arrangements for the vehicle.
What are your local electrical regulations with regards to vehicle earth systems?
Im not using any appliances outside.
Current earthing arrangements are, a dedicated earth busbar which is connected to the chassis in one place only, with the 24v battery pack, the inverter casing, the solar charge controller casing all connected to the earthing busbar.
See very rough drawing below...
My question is this, if a fault developes between the inverter live(line) and the vehicle chassis/metal skin, would it potentially go through the person touching the vehicle to earth? My understanding is, that it would not, since to get to a zero potential, it needs a path back to the inverter. However an electrician friend insists that i need a ground rod for rcd devices to work. To my mind, if i connect an earth rod, then this provides a path, through the hot skin, through the person, through the earth and back up the earth rod through the vehicle chassis earth to the inverter. Would this not be more dangerous potentially?
I thought i had all this 'grounding/earthing' sorted, but now a qualified electrician friend has thrown a spanner in the works. He does 'qualify' his statement with the fact he has not worked on any 'mobile' situations.... but simply cannot get past that the rcd must have a fault path to 'physical earth' to work properly.
Your "stick man" only seems to contact chassis (dc negative) ??
I agree with your thinking. Current can't flow through the stick man unless there IS a rod in the ground.
Your electrician may be correct if he is working with local regulations to which he complies. If an appliance like a power tool, or electric BBQ is to be used outside of the vehicle then regulations may require the vehicle to be referenced to physical earth outside.
I'd follow what your electrician recommends.
A hot to neutral fault inside or outside the trailer will trip the RCD or a circuit breaker. That IS the intent of the neutral/safety ground connection at the source of power.
If the device outside the RV does not have a safety ground connection and there is a fault then the case of that device is elevated to AC hot potential BUT the RCD will trip if your stick man finds a path back to AC neutral.
I should point out that a ground rod does NOT provide a low enough resistance path to trip a circuit breaker, but would be sufficient to trip an RCD.
There are two ground connections that share the same wiring but address completely different issues. The "safety ground" provides a fault current path back to the service entrance or the source of power. In an off-grid situation, that source of power would be your inverter. The safety ground for all AC branch circuits would be connected to the inverter's PE connection through your power distribution panel.
The safety ground is also connected to "earth" via a ground rod. This connection drains off any static charge that might build up should there be no earth connection. When the RV is plugged into shore power, the safety ground also provides a path to earth to drain static charge.
Since your RV is sitting on rubber tires, it could develop a static charge. Touching the RV while standing on the ground could discharge the static. There are other possible static discharge paths such as the RV's metal stairs but not as good as a ground rod.
So I'd say its safer with a ground rod.
@kevin Gr I was just about to create a question for my situation until I read this.
I just installed a Multi-Plus II, Smart Solar MPPT 150/100, Cerbo Gx and 2 x UP2500 Pylontech batteries in my tiny home. All the gear is properly earthed to my chassis. I did not install an earth rod (to comply with the Australian Standard for Electrical Installations in Transportable structures). When I was charging my batteries for the first time using grid power through my Multi (Bulk phase), I opened the metal door to my battery cabinet (which is connected to my chassis) and felt a bit of a shock on my hand. I had no shoes on and it was evident that I had become a path to earth so I went and put my shoes on to inspect further. I removed the grid power and double checked all my cabling. All checked out fine. I was trying to understand why no RCD's were tripping if there was a fault current in the earth circuit.
Your answer here provides a lot more clarity. Static charge. It makes complete sense now. Explains why it was only a small shock, similar to shocks I have had from small car batteries. I was heading in the direction of installing a ground rod anyway but this has helped a lot, thank you.
I have attached some photo's for context for anyone else wanting info in this subject.
MPPT earths through the DC negative buss bar which connects to chassis connection point.
Inverter case earths straight to chassis connection point.
Inverter "PE" earths through buss bars in AC fuse box to DC Negative buss bar.
