Can inverter chassis ground connect to negative dc inverter terminal?

[DerpsyDoodler]

Do I have to run a cable all the way to motohome chassis ground from inverter chassis, or can i simply tie the inverter chassis ground to the battery negative inverter terminal? the battery negative bus bar is connected to chassis ground, already.

what are the ramifications of sharing the inverter battery negative cable in this manner? are there reasons it should not be done?

 

[DerpsyDoodler]

bump

 

[JMc]

One possible scenario: the battery negative cable might be disconnected. In grounding and bonding there are 50 ways to go wrong, if you can think of 25 of them you are a genius.

 

[chrisski]

The battery grounded to the frame is with the intention of running low amperage loads like small light bulbs not high amperage items like DC leveling jacks.

I suppose somewhere hidden in the NEC code you have to pay to access is a standard. If you look up the ABYCC code, you can download for free an older version. This limit may be in there.

 

[DerpsyDoodler]

The battery grounded to the frame is with the intention of running low amperage loads like small light bulbs not high amperage items like DC leveling jacks.

Are you talking about using the chassis as a return path? This is not my intention, and is what i am avoiding. inverter chassis grounded to motorhome chassis is done to (among other things) protect from an energized inverter chassis in the case of a fault. it shorts to ground pulling enough current to pop fuses/breakers.

In my case, i have bonded the battery negative bus bar to motorhome chassis.

The only question i really need answered is: is it safe to bond the inverter chassis ground to the inverter battery negative terminal, directly?

i don’t want to have to do a 3 or 4 awt run any more than necessary.

 

[chrisski]

Not sure if the negative bus bar also grounded to the chassis can be used.

I decided to bind chasis to a hole I drilled and put a star washer and grounding lug with a piece of multistrand insulated 8 AWG wire. My owners manual said bond to chassis with that type of wire In that way.

I thought about bo doing to the negative bus bar since it was tied to ground, but did not. That certainly would have been easier. I did find plenty of places to drill for grounding that was not the beam.

 

[Supervstech]

The only question i really need answered is: is it safe to bond the inverter chassis ground to the inverter battery negative terminal, directly?

i don’t want to have to do a 3 or 4 awt run any more than necessary.

Safe... maybe under some circumstances... but the inverter grounding lug is for reliable under all circumstances fault path.
It should have its own ground conductor connected to its own grounding point.

You do not want a safety ground connected to a current path.

 

[DerpsyDoodler]

Safe... maybe under some circumstances... but the inverter grounding lug is for reliable under all circumstances fault path.
It should have its own ground conductor connected to its own grounding point.

You do not want a safety ground connected to a current path.

OK. Follow-up question. Since it is only a safety ground, can I bond to chassis anywhere on the motorcoach or do i/should i run the inverter chassis ground back to the same chassis ground as the motorcoaches’ chassis batteries?

i ask because there will be a dc dc charger for charging house batteries off the alternator. i do not want to have to worry about isolated vs non-isolated chargers and i am going out of my way to make sure i’m not using chassis as a return path for any house circuits. I do not want galvanic corrosion to be a concern.

 

[chrisski]

OK. Follow-up question. Since it is only a safety ground, can I bond to chassis anywhere on the motorcoach or do i/should i run the chassis ground back to the same chassis ground as the motorcoaches’ chassis batteries?

You don't need to go all the way to the same place. For this type of ground, if the inverter is faulted and sending current through the inverter chassis, you want this going to a good vehicle chassis ground on the shortest route with the least resistance possible.

 

[Supervstech]

You don't need to go all the way to the same place. For this type of ground, if the inverter is faulted and sending current through the inverter chassis, you want this going to a good vehicle chassis ground on the shortest route with the least resistance possible.

Correct.

 

[DerpsyDoodler]

You don't need to go all the way to the same place. For this type of ground, if the inverter is faulted and sending current through the inverter chassis, you want this going to a good vehicle chassis ground on the shortest route with the least resistance possible.

Thanks for your response!

 

[DerpsyDoodler]

Correct.

thanks for your response, as well.

 

[Tecnodave]

Let’s be clear here......The inverter ground lug is to ground the AC side of the inverter, NOT the DC side, now we are in NEC territory......the reason is so that the AC side is referenced to ground.....the DC side of the inverter is already at ground by the negative cable going to the negative post of the battery.....it should not be frame grounded, it (the DC input) of the inverter should go to the battery negative post of the battery which feeds the inverter. The inverter ground lug wires to the AC output of the inverter and the ground lug on the output connector or cabling to a distribution box (breaker panel) and should go to the frame rail closest to the inverter. This is where the NEC comes in, it is to protect YOU, not the inverter. ABYC can be referenced but ABYC does not relate to vehicles it relates to Boats and Yachts (American Boat and Yacht Club). The proper reference for vehicles is the SAE. Society of Automotive Engineers.

Bottom line in a vehicle that has both DC for the vehicle and AC for other needs, not for the vehicle:

Below 48 volts.....SAE rules apply
over 48 volts........NEC rules apply

ABYC is way more conservative than SAE so it if safe to refer to ABYC for a vehicle,
it is not safe to use SAE for an ABYC situation

standards......
14 ga wire in a house..NEC....15 amps maximum if the load is less than 2 hours, if more than 2 hours down rate to 80%
14 ga wire in vehicle....SAE......45 amps!

In any case the AC side is to be “bonded” to ground at one place and one place only, it could be grounded at the inverter or in the distribution box but not both, circulating currents are the reason for this, it would repeatedly trip GFCI’s if circulating currents were to occur.

 

[DerpsyDoodler]

Let’s be clear here......The inverter ground lug is to ground the AC side of the inverter, NOT the DC side, now we are in NEC territory......the reason is so that the AC side is referenced to ground.....the DC side of the inverter is already at ground by the negative cable going to the negative post of the battery.....it should not be frame grounded, it (the DC input) of the inverter should go to the battery negative post of the battery which feeds the inverter. The inverter ground lug wires to the AC output of the inverter and the ground lug on the output connector or cabling to a distribution box (breaker panel) and should go to the frame rail closest to the inverter. This is where the NEC comes in, it is to protect YOU, not the inverter. ABYC can be referenced but ABYC does not relate to vehicles it relates to Boats and Yachts (American Boat and Yacht Club). The proper reference for vehicles is the SAE. Society of Automotive Engineers.

Bottom line in a vehicle that has both DC for the vehicle and AC for other needs, not for the vehicle:

Below 48 volts.....SAE rules apply
over 48 volts........NEC rules apply

ABYC is way more conservative than SAE so it if safe to refer to ABYC for a vehicle,
it is not safe to use SAE for an ABYC situation

standards......
14 ga wire in a house..NEC....15 amps maximum if the load is less than 2 hours, if more than 2 hours down rate to 80%
14 ga wire in vehicle....SAE......45 amps!

In any case the AC side is to be “bonded” to ground at one place and one place only, it could be grounded at the inverter or in the distribution box but not both, circulating currents are the reason for this, it would repeatedly trip GFCI’s if circulating currents were to occur.

that seems like some good information. i’ll have to look into sae and see exactly what its stated purpose/mission is. i’ve done my due diligence when it comes to grounding, and i have an inverter with a built-in dual transfer switch (shore and generator capable). it handles switching of ground paths when connected to shore and includes detailed specifics on the way grounds need to be wired.

this question sprouted from my own perceived gaps in knowledge. i short-changed myself. if i‘d stepped through all of these details in attempt to answer my own question, i’d have been able to answer it.

I have to do what I was originally going to do, which is give it its own line to a common motorcoach chassis ground (or a common grounding bar that has a single connection to that common chassis ground). in my case, since i will potentially be using a non-isolated dc dc charger, that common chassis ground needs to be the same one that the coach chassis batteries are connected to.

Thanks, everyone, for the input. it all helped answer my question.

 

[Solar_Lex]

I have a question that I haven't been able to find on the Internet yet. Why can't I use the vehicle's chassis as inverter's AC neutral, AC Earth ground, and DC negative?

I understand why I want my inverter's Earth ground attached to the chassis so I'm doing that.

I understand the wire money-saving benefits of the DC negative on chassis so I'm doing that.

I just don't get why the AC neutral can't also be attached to the Chassis. Since In my head, AC neutral is the power "return" and earth ground is the "return" in a situation where a live wire touches the bare metal on the vehicle. At first, I was thinking you don't want the chassis used as a neutral wire in case you hold a live wire while you accidentally touch some bare metal of the vehicle. But if the AC earth ground is already attached to the vehicle it doesn't matter the electricity will go through you either way.

 

[Supervstech]

I have a question that I haven't been able to find on the Internet yet. Why can't I use the vehicle's chassis as inverter's AC neutral, AC Earth ground, and DC negative?

I understand why I want my inverter's Earth ground attached to the chassis so I'm doing that.

I understand the wire money-saving benefits of the DC negative on chassis so I'm doing that.

I just don't get why the AC neutral can't also be attached to the Chassis. Since In my head, AC neutral is the power "return" and earth ground is the "return" in a situation where a live wire touches the bare metal on the vehicle. At first, I was thinking you don't want the chassis used as a neutral wire in case you hold a live wire while you accidentally touch some bare metal of the vehicle. But if the AC earth ground is already attached to the vehicle it doesn't matter the electricity will go through you either way.

If neutral is attached to chassis ground, the vehicle will have voltage on it at all times...
Very dangerous.

 

[Solar_Lex]

If neutral is attached to chassis ground, the vehicle will have voltage on it at all times...
Very dangerous.

putting it in those words makes complete sense. 120 volts on frame is dangerous indeed. i seem to miss that when thinking it over haha.

 

[Tomthumb62]

Safe... maybe under some circumstances... but the inverter grounding lug is for reliable under all circumstances fault path.
It should have its own ground conductor connected to its own grounding point.

You do not want a safety ground connected to a current path.

So if I connect the inverter chassis to the trailer chassis and the trailer chassis is connected to the tow vehicle battery ground through the TV chassis (I have not confirmed this at the 7-pin), I don't believe this is a problem, correct? Because it doesn't make a full circuit, correct?

 

[Supervstech]

So if I connect the inverter chassis to the trailer chassis and the trailer chassis is connected to the tow vehicle battery ground through the TV chassis (I have not confirmed this at the 7-pin), I don't believe this is a problem, correct? Because it doesn't make a full circuit, correct?

Inverter chassis and trailer chassis and vehicle chassis can all be in the ground path just fine.
No circuit exists. It's just a balance point for metal to be sure they are at same potential.

 

[Tomthumb62]

Inverter chassis and trailer chassis and vehicle chassis can all be in the ground path just fine.
No circuit exists. It's just a balance point for metal to be sure they are at same potential.

Thanks for confirming that. So should the trailer 12v lifepo4 battery negative be connected to the trailer chassis, too? What's the benefit of this, safety wise? I have no intention of using the chassis for creating any circuits. Thanks, still trying to understand grounding in a mobile situation (I understand it's not really a true ground, cause rubber tires).