Do I need the ground lug to connect my new converter charger

In regards to BFL13, yes the battery disconnect should be on the positive conductor for just that reason so you don't have any 12 volt circuits energized.

According to NEC 551-4(c) bonding voltage converter enclosures, the noncurrent-carrying metal enclosure ... shall be bonded to the frame of the vehicle with a No. 8 AWG copper conductor minimum or equivalent. It further states the grounding conductor for the battery and the metal enclosure may be the same conductor. There are many other sections re: low voltage and battery grounds but the only low voltage items that can use the vehicle chassis as a ground return path are the vehicle's exterior lights ie: stop, turn, tail, markers. Any other low voltage circuits must return to the distribution panel's neg. bus.

Why was this a question in the first place?

If you do not understand the purpose of each of the leads on the unit, maybe time to let someone qualified hook it up.

Is there any way you can get a shock from the chassis if it is not grounded?

You can use the deck mount as a power supply with the neg DC output going to the neg DC input of whatever is being powered. That thing being powered not being a battery that is "neg grounded". EG an inverter.

The chassis ground lug on the outside is where on the inside the green ground wire of the 120v input goes while the white and black go to the board (the black has a glass fuse there)

The RV is one giant "multiple grounds" collection, so that can't be a no-no. EG:

There was a note years back about using a deck mount instead of the "lower portion" (converter part) of a power centre. It said the lower portion in its metal case is touching the metal case of the power centre, which in turn is grounded to the RV frame via the bare copper wire of the 120v shore cord input that has its black to the Main breaker and white to the N buss. The note said the deck mount would not be touching, so it needed its own chassis ground. I don't know why it would need that.

In that case the lower portion converter 120v input did not have a green wire, just the white and black (eg 7300 converter) The DC fuse panel has 12v negs that also go to the frame eventually. You can put your meter on a pos lug and the neg lug and see 12v or you can put the neg lead on the metal power centre metal chassis instead of the DC panel neg lug and still see the 12v

The RV frame shares being the "ground" for 120v and 12v and there can be complications with some inverters which have GFCI outlets. You can get things from the 12v side tripping the inverter's 120v GFCI doing whole house with shore cord into the inverter.

In the 5er when I had the battery disconnect switch on the neg path near the battery, I still had 12v to the RV. There was a neg path via the inverter internals and its chassis ground that by-passed the battery switch. The shore cord was plugged into the inverter and that is how the 12v got back to the frame and so to the 12v neg so the lights and fans still worked. (Should have stuck with using a disconnect on the pos path in that case)

So multiple "grounds" are how RVs work (or don't work if something is wrong)

The chassis ground would only be for a permanent installation. Not needed for portable use.

Thanks, you all just reinforced my thoughts. So for now yes it will be additionally grounded when in the trailer. But when it's sitting on the garage floor charging batteries it will only be grounded through the negative to the battery. The additional ground lug will be ignored.

I did send a question to the Powermax people with the same question. I'm curious what kind of response I'll get.

I presume wa8yxm is referring to a ground loop situation. But I agree that since the ground lug is there use it in the RV. Besides if you mount it on a metal frame member... Wait - 3rd ground?

Well.. You should likely ground it. But my personal opinion... Don't matter it's grounded already via othere leads and multiple grounds is NOT a good idea where I sit.

Theoretically the negative to the battery & a direct to frame from the ground lug are the same.

There is nothing wrong with redundancy. There must be something nearby that the ground can be run to. My theory is that if the ground was not needed the lug on the charger would not be there.

I don't bother with the "chassis ground" with my deck mount converters.

My Vector inverter user's manual says its chassis ground is to reduce radio and tv interference, but I don't know if that is what it is for on a converter.

Might as well add this photo of when I used the chassis ground as an anchor for a strain relief where I was having trouble with heavy cables with silky strands staying in the set screw terminals. That was on a 100 amp PowerMax. Never know--somebody might find that method useful.



The don't mix grounds thing also came from the inverter world where you must not bring the chassis ground around to the neg input. Instead the chassis ground goes to the frame independently.