Finding circuit neutrals for inverter

Does anyone know of a way to find a specific circuit neutral without disconnecting wires from neutral buss bar? Per Magnum docs, circuits powered by the inverter need to have neutrals on their own buss. I can access the main buss bar with one hand but would have difficulty reinstalling screws if removed. When I isolate the neutrals for the 6 circuits I will power from the inverter, I will install new ring terminals. I have enough free wire length to snip the wires from the original buss and move inverter buss to a more accessible location. I just need to find them!!

Any thoughts?

Is there enough room and wire slack to get a clamp on ammeter around each neutral? If so you can turn on something- an appliance or similar on each suspect circuit and check for amperage on that neutral.

That is the only way I can think of without disconnecting each neutral which I assume you are saying is too difficult.

David

You want to be careful when disconnecting a neutral.

if there is a load on a circuit and you disconnect the neutral, the neutral becomes energized.

Making headway with neutrals

I made some headway this afternoon. For safety, I switched off all circuit breakers and disconnected the shore power cable, including the AC! I ran a wire extension from the neutral side of the receptacle for circuit I wanted to isolate. using an OHM meter, I established a reading from the extension wire to the buss bar. Working a screw driver through the wire bundles, I was able to loosened, NOT removing, the terminal retaining screws. By loosening one screw at a time, I was looking for an increase in resistance or open circuit. With the meter clipped to the wire and the buss block, wiggling the loose wire made the meter reading jump around. I found 4 of my 6 circuits before the 95 degree heat got me. Back for the remaining 2 in the morning.

Greetings,
Mr. AB. I hope you turned off the inverter as well...

Maybe this is possible? Per their instal...

Info: The inverter’s NEUT IN and NEUT OUT terminals are electrically isolated from each other while inverting. This is related to the neutral-ground bonding requirement and helps prevent ground-loops (see Section 2.6.5 for more information) If the installation requires the input and output neutrals to be connected together, the inverter’s neutral-to-ground connection must be disconnected (see Section 2.6.5).

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Your quoted manual reference raises a good question. I do not know what the ramifications would be, if any, using an ungrounded neutral power source tied to the original neutral buss. Installation would be much simpler. My main panel breakers open both hot and neutral. With neutral open on the feed, I do not know where my ground to neutral would originate. I am approaching the inverter installation as a power source just as the generator with neutral and ground at the source. As I have already identified 4 of the 6 neutrals for the circuits the inverter will power, I will continue that direction.

And your comment about an ungrounded neutral also raises questions. What the hell are they thinking?!?!?! LOL

Back in the day they decided to tie neutral to ground at the box so they didnt have to run that wire on the poles. While it does provide a "safety" factor being tied to ground, it doesnt have to be. The AC load doesnt know its tied to ground or "floating" as they suggest to do.

Ill have to check some time what mine does on pass thru vs. sourcing power. Ground loops are definitely bad.

Alabama Boater said:

Your quoted manual reference raises a good question. I do not know what the ramifications would be, if any, using an ungrounded neutral power source tied to the original neutral buss. Installation would be much simpler. My main panel breakers open both hot and neutral. With neutral open on the feed, I do not know where my ground to neutral would originate. I am approaching the inverter installation as a power source just as the generator with neutral and ground at the source. As I have already identified 4 of the 6 neutrals for the circuits the inverter will power, I will continue that direction.

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The neutral-ground tie is ALWAYS at the power source. If you are connected to shore power, the tie is at the originating panel for the circuit, wherever that may be, but it is on shore, NOT on the boat. If you're running a generator, it will be at the generator, and any switch that changes source from shore to generator must also handle that ground-neutral connection properly. If you are using an inverter, then the tie-in is at the inverter, the source. Marine inverters have a relay that makes that connection when inverting, and breaks it when passing through. It can quickly get complicated, and particularly if you have a boat that has co-mingled neutrals.

If you have an inverter powered while connected to shore power, it will connect neutral-ground, creating a path to ground that is a fault. If your shore power is via a GFI or ELCI protected circuit, that fault can trip the breaker. Many of the new ELCI shore power systems have a central trip point, so if your boat has an improperly connected neutral-ground tie, you may trip the ELCI on shore, and it will more often than not, drop power to whatever's connected to that main breaker- read: a whole pier or multiple piers. This always happens when it's hot, everyone's running A/C, and the marina staff who have the key to the main panel access have gone home for the long weekend. You'll make friends fast!

Thus the caution about connecting all neutrals to the neutral buss for the inverter. If you're contemplating installing an inverter, it would be wise to include some allowance for a MARINE electrician. Not Jim-Bob, the guy who wires houses, or even a commercial dirt electrician, as the marine world is not in their experience sphere. Most have NO CLUE. Ask them about co-mingled neutrals, they'll give you a blank look, since in their world, neutral is neutral is neutral.

Improperly wired AC on a boat is nothing to trifle with, it can cause stray current to enter the water, and create an electrocution drowning condition. Any new inverter install should be completed by, or at least checked by a competent ABYC marine electrician to insure there's no leakage to ground. If you have an inverter, and you trip an ELCI or GFI breaker, it's cause to have an electrician check it.

I just installed a Magnum ME2512 in our boat. I followed the install instructions and everything works as it should. But, when we tried to use shore power that had the new GFI breakers, we triped them at 3 different marinas on a recent trip up the Columbia/Snake Rivers's. So there must be an issue with my install. My normal non GFI shore power in the boathouse works fine. I need to start trouble shooting this an Steves post has given me some direction. Subscribed!

All neutrals found and isolated

Finished my neutral tracing this morning and made up new inverter neutral bus. It will be feed shore power through the transfer relay or isolated with inverter ground when inverting. I did some grounding investigation using an OHM meter between shore neutral bus vs. boat ground bus vs. inverter neutral bus. My meter shows 0.2 OHMs when on shore power at both inverter neutral and shore neutral vs. ground. When shore power cable is removed and panel feed breakers are off, I have mega OHMs between shore neutral and ground buss and 0.2 OHMs between inverter neutral and ground. Unfortunately, I forgot to test what happens with shore power disconnected but with panel shore feed breaker on. I do not know if the 0.2 OHM resistance is acceptable. I need to do more research.

Previously I had made up a 120V inline GFI to verify if my shore AC power wiring would trip when switching on my panel circuit breakers. I ran through this test again and no circuit tripped GFI. I changed out the end plugs from 30A twist locks to standard 3 prong 15A and checked the 6 circuits powered by the inverter. They did not trip GFI until I pushed GFI test button on my plug-in circuit tester. My cruising area has lower grade elecrical serice at the marinas ... haven't run into any new code installations ... yet.

For those interested ... I chose to have my inverter power cabin (includes TV), head, galley outlets, ice maker, microwave, and coffee maker. Gen need to power up for any other.

AB, I believe my inverter neutrals are on my shore power neutral buss. I will need to look into this next week when we are back at the boat. Thanks for the update. FYI on our boat, I broke out three circuits, recepticles for galley & berth and microwave. Being able to use the Kuerig without the generator is awesome but the biggest plus is going from a 40 amp charger to 125.

Too many circuit improvements have occurred since I was doing circuit design. I believe one of the improvements pertaining to inverters is/was to eliminate the old, heavy transformers with electronic switching circuits using transistors, mosfets and SCRs.

These newer designs apparently CANNOT be tied to an external neutral because neutrals (grounded conductor single phase and three phase neutrals) get connected to the grounding wire (bonding) at an electrical load center. The inverter's outputs must not be tied to ground in anyway or something is going to give....tripped breakers, blown fuses, smoking inverters.

Again, I must admit it was years ago when I last designed a power transformer but I can assure you that a 2 KW 60Hz power transformer IS HEAVY, more than likely heavier than an entire 2KW switching inverter.

I use inverters on our boat for automatic power backup. To do so, I had to electrically isolate AC neutrals with a switching relay such that both the dock's 'hot' wire and its associated neutral wire are isolated from the circuits that get switched to the inverters. There must be isolation between an inverter's neutral and AC/DC grounds. Most light weight power inverter neutrals are not grounded conductors as one is familiar with in normal AC power wiring.

ksanders said:

You want to be careful when disconnecting a neutral.

if there is a load on a circuit and you disconnect the neutral, the neutral becomes energized.

Click to expand...

That is true but anyone with just the least bit of sense would unplug the shore power and disable the inverter before working on the electrical panel.

Alabama Boater said:

...I can access the main buss bar with one hand but would have difficulty reinstalling screws if removed...

Any thoughts?

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Just one: Why the heck do they insist on using tiny, slotted screws on these terminals???

At a minimum, Philips head screws, maybe with a tapered tip so they're easier to get the threads started, would be a huge improvement. Or some configuration that avoids tiny screws altogether.

Good discussion on grounds and neutrals, btw. I thought I understood it all but each time I read one of these posts it gets a tiny bit clearer.

The buss bars are probably Cole-Hersy with #10 binding head screws and 1/4" feed terminals ... all brass. The neutral buss is fastened to bulkhead that runs parallel to the keel line. My access opening is at right angles to buss about a foot from this bulkhead. My access issue is from the wire bundles that come down from above (main power panel) and loop back up to the individual buss screws. The terminal screws are staggered to get more connections on the buss thus partially covering some screws. A big help was when I switched from a LED flashlight to a trouble light I could hang in the compartment. The inverter neutral is now on the back compartment wall with straight in access.

It is all wired and working. Just waiting for my Smartgauge to learn my house bank charging profile to monitor SOC.