Burned ground wire on inverter

[sailingunity]

I just uninstalled my old 1kw inverter last night, and found the ground wire leading to the inverter to be charred. The hot and neutral wires were both fine. Anyone know what could have caused this?

[transmitterdan]

Do you mean the green safety AC earth ground or the battery power negative ground?

[sailingunity]

Sorry, the green wire on the 120V side was burned.

[wingless]

Not good.

There should be zero current passing through the green safety ground wire.

The charred condition indicates lots of current being passed through that wire.

Either the boat has a fault or the shore connection has a fault or both.

The problem should be identified and resolved immediately.

[a64pilot]

I am going to bet that the battery side ground wasn’t a good connection, so it grounded through the AC ground side.
Just a guess, but it’s all I can come up with.

[S/V Illusion]

High resistance connections are the typical reason for this - bad/loose connection either on ground or neutral.

[transmitterdan]

The inverter is an old one. Is it a marine rated inverter? If so, what brand?

The reason for asking is that the cheap inverters they sell at truck stops and Chinese outlets like Harbor Freight are not designed for marine use. The “ground” circuit is not designed to be connected to anything other than the green wire which is not ground or earth or anything.

So tell us more about the inverter.

[sailingunity]

Originally Posted by wingless

Not good.

The charred condition indicates lots of current being passed through that wire.

This much is obvious to me! But the question why? Defective inverter? All of the connections looked relatively good to me, even so there *should* never be enough current going through the ground to fry it.

The inverter neutral and hot were wired in through a shore/off/gen switch, with the ground passing through the box. My new inverter will have all AC passing through it, there will not be a transfer switch, just an on/off.

The DC ground and AC earth are not bonded, could that have caused the issue?

[sailingunity]

Originally Posted by transmitterdan

The inverter is an old one. Is it a marine rated inverter? If so, what brand?

The reason for asking is that the cheap inverters they sell at truck stops and Chinese outlets like Harbor Freight are not designed for marine use. The “ground” circuit is not designed to be connected to anything other than the green wire which is not ground or earth or anything.

So tell us more about the inverter.

No it is not a marine inverter, it is a "motomaster" 1000W pure sine wave. It says "mobile inverter" on the casing. If the cheapo inverter was the issue, it won't be for much longer as it is going to be replaced with a victron inverter / charger soon.

[wingless]

Follow basic diagnostic procedures.

Inspect for solid connections. For example, a voltage meter is used on a conductor passing current by measuring the voltage drop through the circuit. Most of the voltage drop should be across the load and minimum at each connection.

Measure the voltage across the green wire connection points, w/ no green wire. If low or high voltage exists, then disconnect low or high voltage systems to discover which one is bleeding voltage / current onto that point.

If a suitable AC or DC ammeter is on-hand, then safely complete that green wire connection and measure the current through that wire.

[S/V Illusion]

Originally Posted by sailingunity

looked relatively good to me, ...

A common lament for a self-inflicted problem. It may be an as yet unidentified problem about which we are all guessing here, however, my first thought is about when/if you routinely check connections by more than simply looking at it/them.

Visual inspection is often a feel-good activity easily missing a bad connection which required tightening and/or removal and cleaning.

This can be a teaching moment to routinely clean all critical high voltage connections.

[transmitterdan]

Then here is my “guess” as to the problem. The inverter AC ground is connected to the battery minus inside the inverter. Somehow you have been sending DC current through that AC ground connection. So there may be an AC device that is connected to your inverter which is also connected to boat DC negative bus. That would be a bad thing. And the inverter is just letting you know about it.

In a properly installed AC system on a boat no AC appliance should be connected to battery negative anywhere on the boat. Make sure you have no AC appliance connected to boat DC negative anywhere.

There must be one and only one place where inverter AC ground connects to boat DC negative. If there are two places where these two circuits meet then you can have huge DC current in the AC ground wire. That is a big no-no.

Another possibility is that the inverter is faulty in some non-obvious way which caused that AC-DC ground circuit to overheat.

Edit to add:

You should never ever connect the inverter ground to shore power ground. Not ever....

A transfer switch must transfer hot, neutral and AC ground. You should never permanently connect shore AC ground to the inverter ground. It’s possible this is the cause of the overheated ground connection.

[Emmalina]

Nobody want to talk galvanic isolator here ?

[a64pilot]

Unless I’m mistaken my AC ground bus and DC ground bus are connected? Have to open the panel to be sure.

[sailorboy1]

Originally Posted by sailingunity

I just uninstalled my old 1kw inverter last night, and found the ground wire leading to the inverter to be charred. The hot and neutral wires were both fine. Anyone know what could have caused this?

Was the old inverter working?

My guess is that someone/something grounded a positive wire to the inverter frame causing a short. Easy to do if someone were to disconnect a positive cable at the inverter without removing power first.