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Old 07-20-2021, 08:00 AM   #1
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AC input to Quattro inverter from generator

A question or three for the electrical gurus…

I tested my generator output prior to connecting to the Quattro AC1 input. Generator output is 120v 60hz. Some questions:

- checking ground with either hot or neutral resulted in a reading of 55-60 volts AC.
- Connecting neutral to hot resulted in 120v.


So, is this safe to connect to the inverter as is? When I test the Shore AC input from the iso transformer to the Quattro, I see 120V AC on the black hot lead, and 0V on the white neutral.

Ideas?
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Old 07-20-2021, 10:54 AM   #2
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A question or three for the electrical gurus…

I tested my generator output prior to connecting to the Quattro AC1 input. Generator output is 120v 60hz. Some questions:

- checking ground with either hot or neutral resulted in a reading of 55-60 volts AC.
- Connecting neutral to hot resulted in 120v.


So, is this safe to connect to the inverter as is? When I test the Shore AC input from the iso transformer to the Quattro, I see 120V AC on the black hot lead, and 0V on the white neutral.

Ideas?
I would double check your nuetral/ground voltage with any kind of load plugged into the inverter. That voltage should not be present.

Your meter is very high impedance (places no load at all on the line) and may just be picking up coupling on the line. If you have a higher end meter, you can put it in Low-Z mode to reduce the impedance of the meter to drop any stray coupling that may be present, but putting any load on the line should achieve the same effect.
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Old 07-20-2021, 11:36 AM   #3
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I would double check your nuetral/ground voltage with any kind of load plugged into the inverter. That voltage should not be present.

Your meter is very high impedance (places no load at all on the line) and may just be picking up coupling on the line. If you have a higher end meter, you can put it in Low-Z mode to reduce the impedance of the meter to drop any stray coupling that may be present, but putting any load on the line should achieve the same effect.
Which voltage do you speak of?
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Old 07-20-2021, 11:49 AM   #4
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Which voltage do you speak of?
The 50-60 volts on your hot/ground, neutral/ground. I may have misunderstood the question, but I thought that voltage was the source of your concern?

If I saw those readings, I'd put my Fluke into auto-lowz mode to see if it's just a coupled signal (likely), or real voltage/current potential.
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Old 07-20-2021, 11:50 AM   #5
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Also, I meant generator, not inverter. Oops
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Old 07-20-2021, 02:57 PM   #6
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The 50-60 volts on your hot/ground, neutral/ground. I may have misunderstood the question, but I thought that voltage was the source of your concern?

If I saw those readings, I'd put my Fluke into auto-lowz mode to see if it's just a coupled signal (likely), or real voltage/current potential.
Voltage from the generator is the concern- I know it's AC, but should the neutral from the genset show 110v, 60v, or 0 v?

Also, the iso transformer negates the shore neutral to the inverter, so am i correct in assuming that that is the reason for the 120v shore input, and 0v from the neutral?
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Old 07-20-2021, 03:44 PM   #7
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Voltage from the generator is the concern- I know it's AC, but should the neutral from the genset show 110v, 60v, or 0 v?

Also, the iso transformer negates the shore neutral to the inverter, so am i correct in assuming that that is the reason for the 120v shore input, and 0v from the neutral?
Neutral/Hot should show 120v. Neutral/Ground, 0v, just like you are measuring from your iso transformer output. Your pedestal should also show the same voltages.

For some reason 50/60 volts is indicating on the Neutral/Ground and Hot/Ground out of your genset. It's likely this is an inductive coupling from the wiring in your boat all running in the same sheath. Your meter is such a small load (almost non existent) that it is seeing voltage on the ground wire even though there is no electrical connection to a voltage source, it's picking it up inductively like a transformer.

However, it is also possible there is an issue with the generator and there is a real voltage potential on the ground wire, enough that it could carry current. You'd trip ELCI pedestals if that was the case, except your ISO transformer would be hiding that from the shore power connection.

I'd hesitate to connect the generator to the inverter until you get to the bottom of why the 50/60 volts is present from hot/ground and neutral/ground. A low-z reading should eliminate the concern, assuming it reads 0V on that setting, there's no issue.

If you don't have a low-z capable meter (My Fluke 117 can do so, for this exact type of reason) then having a load on the inverter may consume any coupling on the ground line, but that's not guaranteed and you could still be floating a coupled signal on the ground line.

Another alternative to see if it's just inductive coupling, place a 10K Ohm resistor from neutral to ground then measure with your existing meter, you probably want to put the resistor in with the power off The 50/60 volts should disappear. If it doesn't you've got a leakage somewhere.

Hopefully that makes sense.
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Old 07-20-2021, 05:15 PM   #8
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Neutral/Hot should show 120v. Neutral/Ground, 0v, just like you are measuring from your iso transformer output. Your pedestal should also show the same voltages.

For some reason 50/60 volts is indicating on the Neutral/Ground and Hot/Ground out of your genset. It's likely this is an inductive coupling from the wiring in your boat all running in the same sheath. Your meter is such a small load (almost non existent) that it is seeing voltage on the ground wire even though there is no electrical connection to a voltage source, it's picking it up inductively like a transformer.

However, it is also possible there is an issue with the generator and there is a real voltage potential on the ground wire, enough that it could carry current. You'd trip ELCI pedestals if that was the case, except your ISO transformer would be hiding that from the shore power connection.

I'd hesitate to connect the generator to the inverter until you get to the bottom of why the 50/60 volts is present from hot/ground and neutral/ground. A low-z reading should eliminate the concern, assuming it reads 0V on that setting, there's no issue.

If you don't have a low-z capable meter (My Fluke 117 can do so, for this exact type of reason) then having a load on the inverter may consume any coupling on the ground line, but that's not guaranteed and you could still be floating a coupled signal on the ground line.

Another alternative to see if it's just inductive coupling, place a 10K Ohm resistor from neutral to ground then measure with your existing meter, you probably want to put the resistor in with the power off The 50/60 volts should disappear. If it doesn't you've got a leakage somewhere.

Hopefully that makes sense.
YouTube research - seems I need to bond the ground and the neutral. This is exactly what I'm seeing voltage wise (skip to the 3:00 mark):



Nothing is connected as of yet. Now I have to find a way to bond the neutral and ground before connecting to the inverter....
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Old 07-20-2021, 05:22 PM   #9
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Yes you could only see the ground voltage if the output is not bonded to neutral. If they are bonded, there can not be any voltage difference.
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Old 07-20-2021, 07:35 PM   #10
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There should be a ground/neutral bond on the generator. And when the inverter is inverting it should bond them internally. Basically, it should be bonded at the active source, but nowhere else.
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Old 07-20-2021, 08:11 PM   #11
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Many of the small portable generators aren't bonded neutral to ground. Presumably yours isn't since you are seeing the voltage on the neutral line.

Are you planning to hook it to your shore power connector and have that feed into your inverter transfer switch input or are you adding a source switch with a new inlet behind the iso transformer?

More details on what you are trying to do would help
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Old 07-20-2021, 10:57 PM   #12
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YouTube research - seems I need to bond the ground and the neutral. This is exactly what I'm seeing voltage wise (skip to the 3:00 mark):



Nothing is connected as of yet. Now I have to find a way to bond the neutral and ground before connecting to the inverter....
Peter, you are correct... You need to connect generator neutral to ground.

This will solve the problem you are seeing where the generator neutral to ground shows a voltage.

Also on the load side of the isolation transformer you need to have a neutral to ground bond.

Your Quattro will also bond neutral to ground when in invert mode. It will open that bond when either AC source is being passed through by the internal transfer switch.

Are you using both inputs AC inputs into your Quattro??? or are you switching the input manually between shore and generator?
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Old 07-21-2021, 06:22 AM   #13
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I agree that the 50-60V between generator ground to neutral, and ground to hot is because the neutral isn't bonded to the ground in your test.


But you need to step back and understand how your boat's neutral to ground bonding is intended to work. A lot of commonly given advice is correct, but assumes a galvanic isolator, not an isolation transformer.


With an isolation transformer, it's possible (and I think preferable) to bond the neutral and ground on the boat in one permanent location, and have a common neutral throughout the boat. There would NOT be separate bonding points at the generator or inverter, and you would not use any bonding relay capability in the inverter. When you connect the generator to your power system, it utilizes the central ground to neutral bonding. But if the generator is not connected via some selector switch then it's ground and neutral will not be bonded via the boat's central bonding connection, will have a floating ground, and give exactly the sort of readings you are seeing.
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Old 07-21-2021, 09:58 AM   #14
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Peter, you are correct... You need to connect generator neutral to ground.

This will solve the problem you are seeing where the generator neutral to ground shows a voltage.

Also on the load side of the isolation transformer you need to have a neutral to ground bond.

Your Quattro will also bond neutral to ground when in invert mode. It will open that bond when either AC source is being passed through by the internal transfer switch.

Are you using both inputs AC inputs into your Quattro??? or are you switching the input manually between shore and generator?
The boat was set for manual switching between ship and shore prior to the Quattro install last year. Currently, the AC2 input is being used (from iso transformer to Quattro) and it has worked flawlessly switching between shore and inversion via the internal transfer switch.

The final piece is to connect the generator to the AC1 input and utilize the functionality of the Quattro to switch between the AC sources.

Is there an easy way to bond generator neutral to ground?
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Old 07-21-2021, 10:03 AM   #15
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The boat was set for manual switching between ship and shore prior to the Quattro install last year. Currently, the AC2 input is being used (from iso transformer to Quattro) and it has worked flawlessly switching between shore and inversion via the internal transfer switch.

The final piece is to connect the generator to the AC1 input and utilize the functionality of the Quattro to switch between the AC sources.

Is there an easy way to bond generator neutral to ground?

There's likely a way to do it in the wiring box on the generator where the output connections are made.
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Old 07-21-2021, 10:37 AM   #16
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With an isolation transformer, it's possible (and I think preferable) to bond the neutral and ground on the boat in one permanent location, and have a common neutral throughout the boat. There would NOT be separate bonding points at the generator or inverter, and you would not use any bonding relay capability in the inverter. When you connect the generator to your power system, it utilizes the central ground to neutral bonding. But if the generator is not connected via some selector switch then it's ground and neutral will not be bonded via the boat's central bonding connection, will have a floating ground, and give exactly the sort of readings you are seeing.
TwistedTree, where would you expect to perform the dedicated bonding at?

This seems like the best solution, but you'd need to ensure that each source device has it's internal bonding disabled. As it stands, the ISO transformer should have it's own bonding which is passed through the inverter's transfer switch when using shore power. When the inverter is the source it's enables it's internal bonding.
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Old 07-21-2021, 12:24 PM   #17
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TwistedTree, where would you expect to perform the dedicated bonding at?

It can be done pretty much anywhere. My boats have had the bonding in the main electric panel.


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This seems like the best solution, but you'd need to ensure that each source device has it's internal bonding disabled. As it stands, the ISO transformer should have it's own bonding which is passed through the inverter's transfer switch when using shore power. When the inverter is the source it's enables it's internal bonding.

Correct, bonding is always in one, and only one location. The whole problem of bonding locations having to move around on boats is because when on shore power, the bonding is otherwise required on the shore side. Then, because of the "one and only one location" rule, it means you can't bond on the boat.


But then as soon as you disconnect shore power, you are suddenly unbonded and now need to bond somewhere on board. Since it's generally done "at the power source", it's common to have a bonding connection inside the generator.


That works fine except for when you are running just off an inverter and the generator isn't connected to anything, thereby once again losing your bonding connection. So now it's common to bond on the output of the inverter, but it needs to be switched so it's only bonded when you are in inverter mode, and not bonded when the inverter input is connected to shore or gen power since each of them provides bonding.


By now it should be pretty clear why this is such a confusing discussion every time it comes up. Most boats are a confusing mix of bonding connections, each of which is connected under certain circumstances, not under others, and hopefully always one and never more than one. Just makes your head spin, doesn't it? And just to complicate things further, as GFCI and RCD breakers are increasingly used, they can be tripped when these bonding points switch from one to another.



Instead, if you have an isolation transformer, this can be much, much simpler. With an iso, the boat's ground is never connected to the shore power ground. As a result, there is no need for a patchwork of bonding solutions, and you can simply create one single bonding point on the boat and be done with it. Now general rules call for the bonding point to be "at the power source", but your boat has multiple power sources (typically shore, gen, and inverter) that get used in different combinations. So you have to make some choices. The cleanest I've seen is to bond at the central AC power distribution point, and leave the generator and iso unbonded. Then, when you connect the generator via your selector switch, it joins the bonded central power system. Same when you switch to shore power and connect to the output of the iso. The output of the inverter connects to the central power system, so it's bonded, and it's input will be bonded if it's connected to the gen or iso.


OK, that's a mouthful, but there you have it.
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Old 07-21-2021, 12:36 PM   #18
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It can be done pretty much anywhere. My boats have had the bonding in the main electric panel.

...

Instead, if you have an isolation transformer, this can be much, much simpler. With an iso, the boat's ground is never connected to the shore power ground.

...
This certainly seems like the cleanest solution, and is what the unbonded generator is expecting to be connected to, hence the reason it's not bonded. Just need to make sure the other devices are capable of disabling their bonding connection which will vary by brand/model.
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Old 07-21-2021, 12:45 PM   #19
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Twistedtree,

Did you put an iso transformer on your new boat? Which one did you use? I'm assuming your boat is 50A service?
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Old 07-21-2021, 02:05 PM   #20
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Twistedtree,

Did you put an iso transformer on your new boat? Which one did you use? I'm assuming your boat is 50A service?


Yes. One is standard equipment. There are two 50A shore cords, and traditionally one is for ships power and the second dedicated to HVAC. The ship’s cord includes an iso transformer, and the HVAC has a galvanic isolator.

I took a different approach and used two iso transformers, one for each shore cord. Then built a custom switch box that lets either cord be used to power any of three load panels. The load panels are 1) inverter loads, which is everything except what’s on the other panels. 2) is HVAC, and that can additionally be powered off the inverters if you want. 3) non-inverter loads which are electric HW heater elements, shore chargers. It seems complicated, and it is. But it allows for auto start on either generator, and automatic load switching when one starts. That includes backup port when dock power fails, something I’m dealing with at the moment with a broken marina.

The iso transformers are Acme/Hubble marine iso transformers, and have inputs for 240 as well as 208V. I added a contractor to switch between the two based on shore power.
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