Do I need to run a wire from my battery - terminal to the chassis on my trailer?

[corn18]

I asked this inside another thread, but now I am ready to test it. I have a 4/0 wire going from battery negative to the chassis. Not sure why I did this. I don't think it is needed. My thoughts to test whether it is needed: unhook that wire and see if everything still works. Everything I have seen on the DC side has 2 wires running to it. I don't think anything uses the frame for the negative path. My only worry is the electric brakes. I looked at them, and they also have two wires running to them. I don't think the e-brake actuator uses the frame as a conductor, either.

Any downside / danger to just giving this a whirl?

 

[BretS]

Everything I've ever seen says you need one, including Victron's wiring guide... I have a 4/0 chassis ground on mine...

 

[corn18]

Everything I've ever seen says you need one, including Victron's wiring guide... I have a 4/0 chassis ground on mine...

To be clear, this is not the chassis ground required for AC stuff. I still plan to chassis ground the 2 inverters (they are actually mounted to the chassis). But that is different from the negative terminal of the battery.

When I install my VE MultiPluss II, I will install the AC chassis ground to the chassis.

I just read through the Victron LiFePO4 battery manual, and it does not show a chassis ground for their batteries.

 

[dweick]

No

Battery negative terminal should not be treated as a ground.

 

[corn18]

No

Battery negative terminal should not be treated as a ground.

Makes me wonder what the heck I was thinking when I switched to LiFePO4 and moved everything into the basement. Must have been my automotive experience clouding my judgement.

 

[dweick]

Makes me wonder what the heck I was thinking when I switched to LiFePO4 and moved everything into the basement. Must have been my automotive experience clouding my judgement.

Don't get me wrong, if a manual for a particular inverter/charger calls for you to ground the battery do it, but batteries are by their nature floating voltage sources that by themselves have no need for a ground anywhere. When working with a car battery the car has a 12V system that needs a fixed ground reference so yeah the battery is grounded in that situation.

 

[BretS]

To be clear, this is not the chassis ground required for AC stuff. I still plan to chassis ground the 2 inverters (they are actually mounted to the chassis). But that is different from the negative terminal of the battery.

When I install my VE MultiPluss II, I will install the AC chassis ground to the chassis.

I just read through the Victron LiFePO4 battery manual, and it does not show a chassis ground for their batteries.

No, I am talking about a ground from the negative bus to the chassis of the RV. It should be the size of your largest DC cable. You also need the smaller chassis grounds off the cases of the components if they require it. Look at any Victron system schematic, explorist life schematic, or Victron's wiring unlimited manual...

 

[BretS]

Don't get me wrong, if a manual for a particular inverter/charger calls for you to ground the battery do it, but batteries are by their nature floating voltage sources that by themselves have no need for a ground anywhere. When working with a car battery the car has a 12V system that needs a fixed ground reference so yeah the battery is grounded in that situation.

How is the 12V in an RV any different? Every system schematic I have seen has a ground from the negative bus to the chassis, and it is sized equal to the largest cable (or at lmost one size down). That is in addition to the smaller chassis grounds from the cases of components.

 

[corn18]

No, I am talking about a ground from the negative bus to the chassis of the RV. It should be the size of your largest DC cable. You also need the smaller chassis grounds off the cases of the components if they require it. Look at any Victron system schematic, explorist life schematic, or Victron's wiring unlimited manual...

You're right! I looked at all the schematics on the VE website and they all include grounding the negative bus to the chassis. Except one, which is weird. This one also doesn't show the chassis ground for the MP, so I don't like it.

Thanks! That answers my question and I will leave the 4/0 chassis ground in place.

 

[dweick]

How is the 12V in an RV any different? Every system schematic I have seen has a ground from the negative bus to the chassis, and it is sized equal to the largest cable (or at lmost one size down). That is in addition to the smaller chassis grounds from the cases of components.

If the battery is dual use, for an inverter and for the vehicle 12V supply then sure it needs to be grounded because the 12V system in a vehicle doesn't float, it grounds to the chassis. But a battery that is just used as part of a 120V power system can float, it doesn't need to be grounded to whatever ground the 120V is tied to. You don't want current flowing through some grounding wire from the battery, that would not be a good thing.

You are perfectly free to put something like a Sol-Ark in an RV, for example, and they don't call for tieing the battery negative to ground.