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Old 11-24-2020, 11:56 PM   #1
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Inverter Chassis Ground

Help please, just had my boat surveyed and he said I need to run a chassis ground of the same size as the inverter leads or one size smaller. Is it OK to run the chassis ground of the inverter directly to the negative post of the house battery bank because they are really close or should it go somewhere else?
Thanks in advance.........
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Old 11-25-2020, 03:18 AM   #2
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It should go to the main ground bus bar.
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Old 11-25-2020, 07:18 AM   #3
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That ground is for AC leakage. Usually AC and DC grounds are tied together someplace common, like the engine block, but not always. You can rely on the battery negative if it is tied to AC ground someplace, but that isn't the best solution. The best is to tie that ground to wherever your incoming shore power ground wire terminates, usually a ground buss near the main AC panel.

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Old 11-25-2020, 08:12 AM   #4
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I think its more than AC leakage if the requirement could be up to 000 wire for big inverters.


My guess is a dead short from the positive battery cable.
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Old 11-25-2020, 09:06 AM   #5
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Originally Posted by rochepoint View Post
Help please, just had my boat surveyed and he said I need to run a chassis ground of the same size as the inverter leads or one size smaller. Is it OK to run the chassis ground of the inverter directly to the negative post of the house battery bank because they are really close or should it go somewhere else?
Thanks in advance.........

If memory serves, chassis ground wire can be one size smaller than the largest other wire used and should be grounded to the main ground buss.
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Old 11-26-2020, 02:25 PM   #6
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It’s a safety connection in case AC were to come in contact with the chassis.

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Old 11-26-2020, 04:04 PM   #7
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https://www.bluesea.com/support/arti...ttery_Chargers


3. Install a DC grounding conductor sized not less than one size smaller than the DC positive conductor and have a capacity such that the DC positive fuse has an amperage rating not greater than 135% of the current rating of this grounding wire. As a practical matter, this wire will be much larger than the AC grounding conductor. This requirement is the latest addition to the standards when it was discovered that faults in the DC side of an inverter or charger could provide sustained high currents that could start a fire from overheating the AC grounding conductor.
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Old 11-26-2020, 04:06 PM   #8
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One should be careful recommending grounding inverters because not all inverters are the same. Inverters predominantly advertised for vehicle use are in the trouble category.

For example, the so called grounded conductor DOES NOT exist in many inverters. So how will one know? In an electrically isolated boat, it might work as long as the grounded (white wire) conductor is not made fast with the grounding conductor (green wire). If they are, you risk immediate breaker tripping. Expensive inverters use transformers to protect against this, cheapies do not.
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Old 11-27-2020, 07:01 AM   #9
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The grounding lead goes the same place as the inverter battery negative connection. That should be nearby too.

Most inverters have this type connection that previously was considered for providing safety from AC shorts. But, if the inverter fails and shorts to the DC side a 10-gauge or so ground wire would burn through its insulation in short order and possibly cause a fire. Your inverter will be protected from AC shorts too if there is a connection between the AC green ground and DC negative busses.

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Help please, just had my boat surveyed and he said I need to run a chassis ground of the same size as the inverter leads or one size smaller. Is it OK to run the chassis ground of the inverter directly to the negative post of the house battery bank because they are really close or should it go somewhere else?
Thanks in advance.........
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Old 11-27-2020, 07:05 AM   #10
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I think in this instance a ground lug on the inverter case was not connected. Nothing to do with attempting to polarize the inverter AC output. That is typically done inside the inverter box automatically.

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Originally Posted by foggysail View Post
One should be careful recommending grounding inverters because not all inverters are the same. Inverters predominantly advertised for vehicle use are in the trouble category.

For example, the so called grounded conductor DOES NOT exist in many inverters. So how will one know? In an electrically isolated boat, it might work as long as the grounded (white wire) conductor is not made fast with the grounding conductor (green wire). If they are, you risk immediate breaker tripping. Expensive inverters use transformers to protect against this, cheapies do not.
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Old 11-28-2020, 08:42 PM   #11
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Thanks everyone!
The ground lug on the case fits a 1/0 cable, now just to decide on the best location to attach the other end. When I took the lug off to check the size it had a few strands of cut off copper wire in it, which was probably remnants from when they remove the boats bonding system five years ago as thats where the PO had it tied into.
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Old 11-28-2020, 09:37 PM   #12
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I think in this instance a ground lug on the inverter case was not connected. Nothing to do with attempting to polarize the inverter AC output. That is typically done inside the inverter box automatically.

Have no clue what you are talking about
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Old 11-28-2020, 10:31 PM   #13
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Help please, just had my boat surveyed and he said I need to run a chassis ground of the same size as the inverter leads or one size smaller. Is it OK to run the chassis ground of the inverter directly to the negative post of the house battery bank because they are really close or should it go somewhere else?
Thanks in advance.........
Pretty sure he is referring to the AC leads, not the DC ones.

Only commenting because you posted regarding a 1/0 ground conductor which is unheard of.
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Old 11-28-2020, 11:21 PM   #14
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Pretty sure he is referring to the AC leads, not the DC ones.

Only commenting because you posted regarding a 1/0 ground conductor which is unheard of.
Hi Kevin
I am talking about a chassis ground back to the DC ground, the surveyor also gave me a link to this page, scroll down about half way to see the chassis ground part.
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