Grounding Power Inverter

[BrettB]

I'm a bit confused on this. From my research, it sounds like I can ground my power inverter directly to the negative battery terminal, so why don't the power inverter companies just save me the trouble and connect the ground to the negative terminal on the inverter, internally?

[model 10]

They want the frame to be bonded to ground. Doing it internally is not the same deal, I think.

[rwidman]

Originally Posted by BrettB

I'm a bit confused on this. From my research, it sounds like I can ground my power inverter directly to the negative battery terminal, so why don't the power inverter companies just save me the trouble and connect the ground to the negative terminal on the inverter, internally?

If you think you have a better idea, write to them and tell them about it. Otherwise, follow the instructions. You can be pretty sure they figured out the best and safest way to do it.

[S/V Illusion]

Negative in the context you use it isn't a ground but rather a return common bond. If you understand that concept, therein lies your answer.

[ranger58sb]

Originally Posted by BrettB

I'm a bit confused on this. From my research, it sounds like I can ground my power inverter directly to the negative battery terminal, so why don't the power inverter companies just save me the trouble and connect the ground to the negative terminal on the inverter, internally?

Our inverter manual instructs connect DC negative terminal to the negative battery post (yellow cable). It also instructs connect the chassis ground terminal to the engine block (green cable).

-Chris

[boatpoker]

This ain't rocket surgery but you clearly don't understand the issues (and there are many other considerations in inverter installation). The potential for hurting someone or starting a fire is significant. Hire an ABYC qualified tech and watch.

[smac999]

same reason you don't connect the white and green together on every AC device.

one carries current. one doesn't carry current, but will in an emergency.

[Jeanneau 45.2]

Some of these replies are a bit harsh in tone, IMHO. The OP clearly didn't know so he asked the question. The forum 'feng shui' thanks the responses provided without editorial comment .....

[boatpoker]

Originally Posted by Jeanneau 45.2

Some of these replies are a bit harsh in tone, IMHO. The OP clearly didn't know so he asked the question. The forum 'feng shui' thanks the responses provided without editorial comment .....

I disagree, stating the facts is to his benefit. The OP is playing with significant amounts of electricity. If he does not understand the requirements for installation he is taking big chances. I'd rather warn him now than post next week .... "So sorry you lost your boat".

[a64pilot]

Inverter grounding is a bit perplexing, it is one place where you can subvert the isolation transformer and inadvertently connect the AC and DC grounds together, thereby of course making you susceptible to stray currents that could be coming on from the shore power ground.

[thomm225]

Originally Posted by ranger42c

Our inverter manual instructs connect DC negative terminal to the negative battery post (yellow cable). It also instructs connect the chassis ground terminal to the engine block (green cable).

-Chris

Some of us have inverters but no engine block to ground them to so we are "floating" but so is all our electronics onboard.

[ranger58sb]

Originally Posted by thomm225

Some of us have inverters but no engine block to ground them to so we are "floating" but so is all our electronics onboard.

Good point. The manual actually said engine ground or the boat's DC grounding bus (and it distinguished between that and battery negative)... afraid I just short-handed it.

For OP, DC connections in our case are actually marked DC+, DC- (negative), and Earth.

-Chris

[zboss]

https://www.jamestowndistributors.co....do?docId=1014

[sailorchic34]

Originally Posted by a64pilot

Inverter grounding is a bit perplexing, it is one place where you can subvert the isolation transformer and inadvertently connect the AC and DC grounds together, thereby of course making you susceptible to stray currents that could be coming on from the shore power ground.

A transformer type inverter acts as a isolation transformer, this is why I don't connect case ground to dc ground. I leave it floating as the inverter is not ground referenced. Yes that does not meet code, but I don't think the boys that wrote the code understood how most inverters work. Inverter power is not exactly the same as shore power.

Isolated power means there is no earth reference and you can come in contact with a hot leg and not conduct current. Used in every Surgery/operating room in the USA. It's as safe as power can be. You have to grab both legs to be in circuit and have current flow from leg to leg only.

It works the same from powering an appliance, but not at all the same from how it's made. Shore power is a center tapped neutral (USA type). USA 120V power, is a 120v hot leg and a zero cross/center tap neutral (Also called split phase).

It's called a neutral as it's at 0V potential (same as ground). It sits at the zero cross point of the 240V leg to leg of typical US residential power transformer. Inverter power both USA and EU have both legs hot (at 60v each leg or 120v leg to leg for EU). Current only flows from leg to leg. There isn't a current flow path to ground as the secondary side has no ground reference or center tap. Very much (Actually exactly) like an isolation transformer. Primary side is or course 12V (or 24v).

USA landside power is earth referenced both at the generating plant and at the point of service. That is there can be current flow from one leg to ground. So grounding makes complete sense there and for boat side outlets on shore power.

There are also non-transformer inverters (IE switching with caps for filtering) and for those a case ground IS 100% REQUIRED, as there isn't a transformer that isolates the 12v from 120V side. That means it is possible to have high voltage on the case with a failure internally.

As the engine block is in many cases wired with large negative ground, there is very little potential difference between the battery - post and engine.

In either case running a case ground generally will not hurt anything.

[a64pilot]

My Magnum MS2812 Is wired into the shorepower cable before the circuit breaker panel, this way when you have no shorepower, it will power the whole boat if you like up to its max capacity of course. However my isolation transformer is immediately before the circuit breaker panel as I believe most are.

My zinc consumption was greatly increased, I wasn’t getting but maybe two months out of a zinc.

By connecting case ground to the green and yellow AC ground, and of course the negative DC ground to the battery bank negative, I had made a connection between the two, prior to the isolation transformer.

Not wanting to disconnect the inverter and have a floating AC ground, I instead moved my isolation transformer so that it is connected to shorepower before the inverter. It’s a little too soon to declare victory, but so far it appears my zinc consumption has returned to normal.