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Old 20-07-2017, 10:17   #1
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Importance and Method of Separating Neutrals on Inverter Install?

My understanding is that if inverter circuits are separated from non inverter AC circuits, the the neutrals also need to be separated. The internet being what it is, and given that identifying which neutral is which can be a real challenge, some have suggested it's not really necessary. So two questions..

1. What are the consequences of not doing it? Is it a safety issue, function issue, or both?

2. Depending on the boat, it could be difficult to figure out which neutrals are which in order to separate them. What would be the simplest method for identifying neutrals for various circuits so that they could be moved to their own buss?

Thanks
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Old 20-07-2017, 10:39   #2
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Re: Importance and Method of Separating Neutrals on Inverter Install?

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>>>>>>>>> What would be the simplest method for identifying neutrals for various circuits so that they could be moved to their own buss?
Turn everything on and remove each neutral from the bus, one at a time, see what goes off, then label each wire.
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Old 20-07-2017, 11:31   #3
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Re: Importance and Method of Separating Neutrals on Inverter Install?

If you have two neutrals on the boat, surely you have two panels, therefore easily identified.

You are not intending to run two services through the same inverter are you ?
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Old 20-07-2017, 11:43   #4
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Re: Importance and Method of Separating Neutrals on Inverter Install?

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If you have two neutrals on the boat, surely you have two panels, therefore easily identified.

You are not intending to run two services through the same inverter are you ?
Not clear on your question. Each AC circuit has it's own neutral tied back to a common buss behind the panel. The scenario is 50amp 125/250V ship service. One hot leg will be powered via passthrough/inverter. The neutral for each circuit of that (inverter) leg should be separated to their own bussbar. But currently all neutrals are on one buss and not labeled.

Looking for a safe and simple method of identifying which neutral goes with which circuit in order to identify which to separate. The suggestion of turning everything on and removing them one by one to see which shuts off would certainly work but working behind a live panel does not strike me as the best idea either.

*edit for clarity
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Old 20-07-2017, 11:55   #5
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Re: Importance and Method of Separating Neutrals on Inverter Install?

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The scenario is 50amp 125/250V ship service.
That was not mentioned in your post. I was assuming two 30amp circuits.
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Old 21-07-2017, 11:35   #6
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Re: Importance and Method of Separating Neutrals on Inverter Install?

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My understanding is that if inverter circuits are separated from non inverter AC circuits, the the neutrals also need to be separated. The internet being what it is, and given that identifying which neutral is which can be a real challenge, some have suggested it's not really necessary. So two questions..

1. What are the consequences of not doing it? Is it a safety issue, function issue, or both?

2. Depending on the boat, it could be difficult to figure out which neutrals are which in order to separate them. What would be the simplest method for identifying neutrals for various circuits so that they could be moved to their own buss?

Thanks

Not separating the neutrals causes neither a "safety issue" nor a "function issue."
Isolating the shore power hot and neutral with a shielded isolation transformer will add value by providing common mode noise and spike attenuation.
Good day to you sir.
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Old 21-07-2017, 14:42   #7
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Re: Importance and Method of Separating Neutrals on Inverter Install?

I have had to correct a number of inverter installations where the original installer failed to separate the neutrals dedicated to inverter-fed circuits. The usual symptom is tripping GFCI breakers because the breakers are seeing differences in their hot and neutral current flows (which indicates a ground fault).

Since most of the circuits that you will want have inverter powered are outlets, identifying them shouldn't be too hard. In theory you have individual breakers each set of outlets, lets say port and starboard, or fore and aft. Make a "jumper plug" by connecting the hot and neutral blades of a male appliance plug, shut all the power off, disconnect all of the neutrals, plug your jumper into one of the outlet circuits, and use a multimeter set to ohms to measure between the hot wire for that circuit and each neutral until you find one that shows connectivity. It should be zero ohms. Mark that neutral and then move on to the next circuit.

On most vessels that I've worked on, including mine, there are only two to four circuits that are inverter powered, usually a couple of outlet circuits, the microwave (if it has a dedicated circuit) and maybe the TV. On some big yachts, the inverter might also support the refer.

Once you've ID'd the inverter neutrals, connect them to their own bus along with the neutral output of the inverter.

Done.

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Old 21-07-2017, 15:07   #8
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Re: Importance and Method of Separating Neutrals on Inverter Install?

Quote:
Originally Posted by Prospective View Post
My understanding is that if inverter circuits are separated from non inverter AC circuits, the the neutrals also need to be separated. The internet being what it is, and given that identifying which neutral is which can be a real challenge, some have suggested it's not really necessary. So two questions..

1. What are the consequences of not doing it? Is it a safety issue, function issue, or both?

2. Depending on the boat, it could be difficult to figure out which neutrals are which in order to separate them. What would be the simplest method for identifying neutrals for various circuits so that they could be moved to their own buss?

Thanks
To be ABYC compliant, the neutral (grounded conductor) may be connected to the green (grounding conductor) at the source. For shore power circuits, this connection is at the isolation transformer (or shoreside distribution panel if none). For inverter power, this connection is at the inverter. Most marine inverters have a pass thru relay to automatically perform the switch. If you do not want all AC circuits to be fed by the inverter, it is best to set up a separate AC distribution panel for those circuits. Remember to install the label at the main shore power breaker of that panel, that the panel is powered by an inverter.

That you are asking rudimentary questions suggests that you have a lot more to learn. Perhaps consider hiring a "Sparky".
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Old 22-07-2017, 11:52   #9
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Re: Importance and Method of Separating Neutrals on Inverter Install?

With all due respect to "Sparky" he/she should not be hired to design wiring for boats. The inverter manufacturer's engineering department should publish shipboard installation instructions that are in compliance with ABS and all other lesser standards. Sparky or any "capable cruiser" should be able to understand the instructions, look at the block diagram of the inverter and install it properly so that GFI receptacles and circuit breakers operate as intended. If we wire boats based on what people typically do, then the hardware will typically work. We will end up with isolated neutrals and a plethora of other myths..... End of sermon.
IMO neutral conductors on board a vessel should be connected to boat ground only with a "high impedance" connection. (see ABS) Boats should be equipped with ground fault protection systems that do not cause sparks when a ground fault occurs. Boats with gasoline fueled engines should be especially careful not to create sparks during a ground fault and this is achieved by not hard wiring neutral to ground. High impedance neutral to ground connection will also be compatible with store bought GFI receptacles and CBs
Cheers.
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Old 22-07-2017, 12:09   #10
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Re: Importance and Method of Separating Neutrals on Inverter Install?

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IMO neutral conductors on board a vessel should be connected to boat ground only with a "high impedance" connection. (see ABS) Boats should be equipped with ground fault protection systems that do not cause sparks when a ground fault occurs. Boats with gasoline fueled engines should be especially careful not to create sparks during a ground fault and this is achieved by not hard wiring neutral to ground. High impedance neutral to ground connection will also be compatible with store bought GFI receptacles and CBs
ABS has very little to do with the type of boats we are concerned with on this forum but having said that, I know little about them other than their FRP standards. ABYC are the "best practice" standards accepted in North America and those standards contradict much of what you say.

For example your scenario of a ground fault causing a spark in a gasoline engine compartment is irrelevant in boats built to ABYC standards due to those standards prohibiting any non-ignition protected equipment in compartments containing any gasoline.

Another example, bonding of neutrals can supply power to appliances that are disconnected by the breaker .... an unsafe condition.

and another .... A poor connection in one neutral may cause excessive current in the other.

There is also potential shock hazard if if one of two shore power cords are not being used.
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Old 22-07-2017, 13:15   #11
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Re: Importance and Method of Separating Neutrals on Inverter Install?

I have a pair of Magnum MS_PAE inverters and originally looked at them because they greatly simplified AC wiring. A single inverter can supply both 120 and 240 AC. You can stack up to 4 for 16kw. Everything runs thru the inverters. When on shore power or generator, the AC passes thru the inverter while it charges the batteries and it automatically shifts to battery when other power is shut off. Magnum also has a device that will start a generator if the batteries get too low. It's easy, except for battery water, I don't think about it.
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Old 22-07-2017, 17:11   #12
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Re: Importance and Method of Separating Neutrals on Inverter Install?

Quote:
Originally Posted by Ahmet Erkan View Post
With all due respect to "Sparky" he/she should not be hired to design wiring for boats. The inverter manufacturer's engineering department should publish shipboard installation instructions that are in compliance with ABS and all other lesser standards. Sparky or any "capable cruiser" should be able to understand the instructions, look at the block diagram of the inverter and install it properly so that GFI receptacles and circuit breakers operate as intended. If we wire boats based on what people typically do, then the hardware will typically work. We will end up with isolated neutrals and a plethora of other myths..... End of sermon.
IMO neutral conductors on board a vessel should be connected to boat ground only with a "high impedance" connection. (see ABS) Boats should be equipped with ground fault protection systems that do not cause sparks when a ground fault occurs. Boats with gasoline fueled engines should be especially careful not to create sparks during a ground fault and this is achieved by not hard wiring neutral to ground. High impedance neutral to ground connection will also be compatible with store bought GFI receptacles and CBs
Cheers.
Ahmet
One would think so but most boats I perform electrical inspections on where the owner believes everything was done correctly is a tragic fire just waiting to happen.
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Old 22-07-2017, 23:30   #13
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Re: Importance and Method of Separating Neutrals on Inverter Install?

if the wires are run as a 3 strand wire into the panel. it's easy to fix. just follow the hot wire you want to move to the inverter panel, follow back to striped wire, and then follow it's N back to the bus. if it's wired in single strand wire, or the N bus is in a different location (IE engine room like grand banks) then it's much harder.

having a common N will trip ELCI or GFI dock breakers. for the same reason it will also bypass a galvanic isolator during the inverter accepting time, or if the inverter input breaker is turned off on the boat, you have a bypassed (non working) galvanic isolator. due to having a N-G bond on the whole boat.
Attached Files
File Type: pdf elci figure 1.pdf (13.0 KB, 44 views)
File Type: pdf elci figure 2.pdf (13.2 KB, 37 views)
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Old 23-07-2017, 14:43   #14
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Re: Importance and Method of Separating Neutrals on Inverter Install?

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ABS has very little to do with the type of boats we are concerned with on this forum but having said that, I know little about them other than their FRP standards. ABYC are the "best practice" standards accepted in North America and those standards contradict much of what you say.

For example your scenario of a ground fault causing a spark in a gasoline engine compartment is irrelevant in boats built to ABYC standards due to those standards prohibiting any non-ignition protected equipment in compartments containing any gasoline.

Another example, bonding of neutrals can supply power to appliances that are disconnected by the breaker .... an unsafe condition.

and another .... A poor connection in one neutral may cause excessive current in the other.

There is also potential shock hazard if if one of two shore power cords are not being used.
I don't want to get into arguments about commercial safety recommendations such as ABYC, I do not agree with everything they recommend as safe. For example the recommended wiring diagrams where an isolation transformer is said to make it safe to disconnect the shore ground from the boat should be removed from ABYC standards before somebody gets electrocuted. (Oh wait, ABYC has covered their backsides with a disclaimer if somebody gets hurt)
Anyway, I will just stick to what I know, which is the basic law of physics, and the fellow sailors are obviously free to believe whomever they prefer. (ie: ABYC or some guy with a funny name)
OK now I will share with you what I learned working in the power engineering industry for about 50 years :
With a hard grounded neutral when a ground fault occurs, the un-grounded power conductor shorts to the chassis of the equipment or the metal hull and the initial short circuit current surge (let through current) before the over current device (CB or fuse) begins to open could be in thousands of amperes making lots of sparks where the short circuit occurred and leaves black marks on the metal etc. A "high impedance Neutral Ground system" which is used on ships (especially warships) limits the fault current by placing a resistor in series with the fault current and actually allows critical systems to operate safely while the ground fault is present and simultaneously activates an alarm to indicate that repairs are needed.
A high impedance ground system will keep you safe at sea when an inverter and/or a generator is operating. The high impedance ground system will also be compatible with the ELCI or GFCI products at the marina without having to separate neutrals on your inverter loads. The only time separate neutrals would be necessary is when powering the boat with multiple shore power cables from the same power source as Mr. boatpoker very astutely pointed out.
If anyone has an interest to implement a high impedance grounding system, I will be glad to provide recommendations in more detail.
All the best and fair winds.
Ahmet
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Old 23-07-2017, 14:53   #15
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Re: Importance and Method of Separating Neutrals on Inverter Install?

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ABYC, I do not agree with everything they recommend as safe. For example the recommended wiring diagrams where an isolation transformer is said to make it safe to disconnect the shore ground from the boat
You'll have to point out to me where it says that. It certainly does not show up in my copy of E-11.
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