neutral bonding issues SS 300 inverter

bobdog · September 2010

(I was going to direct this as a PM to Icarus, but decided to post to the forum)

I've been going through many posts about grounding and neutrals and floating and bonding and a thought just occurred to me and I need advice.

We (Tony and I) have the same inverter MS SS300. It has a floating neutral until you turn it on, at which time it senses the safety ground leg and bonds to it. Is that basically right? Well, the way I have my system set up is I've bonded my grounds and neutrals on one bus bar in my "main" panel. It has 2 circuits. What concerns me is from a picture I saw of your set up (Tony's) in a thread recently, I noticed that you had a grounding wire coming out of one leg of your output wires of the inverter. I assume that it ultimately went to the main grounding point (rod, etc.). So, to my questions.

1. Does having the ground wire come directly out of the inverter force that wire to be the neutral? Is this necessary?

2. I understood that the neutral bonding "sensing" would happen at the main panel where I have my ground/neutral bonded. Am I bonding neutral at 2 points then?

3. I'm worried that if I have neutral bonded inside the inverter and also at the panel I'm bonding it twice. Is that right?

Finally, did the problem about a generator/grounding issue get resolved from a while back? I may have a question or 2 on that, but I'll post to the forum. (Later)

Sorry for the long post and thanks for all the help.

Tim

dwh · September 2010

Re: neutral bonding issues SS 300 inverter

bobdog wrote: »

2. I understood that the neutral bonding "sensing" would happen at the main panel where I have my ground/neutral bonded. Am I bonding neutral at 2 points then?

3. I'm worried that if I have neutral bonded inside the inverter and also at the panel I'm bonding it twice. Is that right?

Yes and yes. I don't know about the inverter, I'll have to leave that to someone else, but if you are bonding neutral to ground in the breaker panel, then that is the one you want to keep and you don't need it at the inverter.

Solar Guppy · September 2010

Re: neutral bonding issues SS 300 inverter

The SureSine doesn't sense anything, its a transformer based inverter so one would connect the neutral to ground at the inverter as its not a whole house inverter.

If you choose to run it to a breaker panel, make the neutral to ground bond there, not at the inverter and with only 300 watts, that seems silly IMHO to have a breaker panel

bobdog · September 2010

Re: neutral bonding issues SS 300 inverter

Solar Guppy wrote: »

and with only 300 watts, that seems silly IMHO to have a breaker panel

Silly as it may be, it allows for future expansion, which is a topic brought up now and again on this forum. Besides it makes me feel like I'm playing with the BIG boys....;)

icarus · September 2010

Re: neutral bonding issues SS 300 inverter

It may seem silly to have a AC breaker box, but it allows you to expand later as suggested by bobdog, but it also allows you to wire your house with branch circuits in a logical layout. I have 6 AC branch circuits in a 600 sq ft house, and that is silly, but it allows me to separate out loads any way I like using the breakers. Additionally I can add a second SS 300 to the 240 breaker box to feed 1/2 the circuits if my loads grow that much.

It mostly just saves a spaghetti of wiring. Even in a larger house, 300 watt is really quite a bit of power assuming you have no motor loads like fridges etc. My biggest single draw is the paddle fan ~50 watts on Medium. I can run a hell of a lot of 15 watt cfls on the 300 watt inverter,, 30 to be exact. We have ~4 on at any time, double the house, and that might be 20??.

Tony

PS To answer the OP, when you ground one side of the inverter output, it becomes the neutral so it goes to the neutral bus in the breaker box, and is in turn bonded and grounded assuming you chose to bond and ground your neutral bus. I don't believe that the SS 300 is truly a floating neutral like many small gennies however. That said, my understanding of floating neutrals is not very good, inspite of Bill's best effort.

Solar Guppy · September 2010

Re: neutral bonding issues SS 300 inverter

The Suresine is 100% floating on the outputs, that's what a transformer does. The only potential is between the output connections

bobdog · September 2010

Re: neutral bonding issues SS 300 inverter

icarus wrote: »

PS To answer the OP, when you ground one side of the inverter output, it becomes the neutral so it goes to the neutral bus in the breaker box, and is in turn bonded and grounded assuming you chose to bond and ground your neutral bus.

I'm not currently at the cabin so this is from memory. I wired the cabin with 12 gauge Romex with the white wires and the bare wires going to a single bus in the main panel. Then I plan to run a ground off of that bus to a grounding rod. The black wires went to circuit breakers.

Further, I wired the output of the SS 300 with a 12 gauge Romex with the white wire going to the neutral/grounding bus in the main panel and the black wire going to the hot bus to "energize" the circuit breakers. The ground or bare wire I cut off and have not used.

So, I guess I'm wired correctly? No? Should I utilize the bare wire in some way?

Thanks for all the help.

Tim

BB. · September 2010

Re: neutral bonding issues SS 300 inverter

On the AC side--Wire just like a house (if isolated inverter output like the SureShine). White to neutral, black is "hot" (so is red). Bare wire goes to metal boxes, ground wires/ground green connection of AC outlet.

12 volt DC grounding--gets a little bit questionable... For a 12 volt car radio, the case is both the negative ground and the safety ground... Double connections with ground returns and DC can get very troublesome.

-Bill

icarus · September 2010

Re: neutral bonding issues SS 300 inverter

Floating is something my boats do,,,How electricity "floats" is,,,,

dwh · September 2010

Re: neutral bonding issues SS 300 inverter

bobdog wrote: »

I'm not currently at the cabin so this is from memory. I wired the cabin with 12 gauge Romex with the white wires and the bare wires going to a single bus in the main panel. Then I plan to run a ground off of that bus to a grounding rod. The black wires went to circuit breakers.

Further, I wired the output of the SS 300 with a 12 gauge Romex with the white wire going to the neutral/grounding bus in the main panel and the black wire going to the hot bus to "energize" the circuit breakers. The ground or bare wire I cut off and have not used.

So, I guess I'm wired correctly? No? Should I utilize the bare wire in some way?

Thanks for all the help.

Tim

Well...

Really the grounds should be into one bus and the neutrals into another. In the main breaker panel you would then bond the neutral bus to the ground, either by bonding it to the metal box itself, or using a jumper over to the ground bus.

You can get away with what you did on a main breaker box, but if you were wiring a sub-panel it would be wrong to run the neutrals and grounds both into the same bus. (Wrong to bond neutral to ground in a sub-panel.)

As for the bare ground wire in the romex from the SS300 - that should connect to the "earth ground" terminal on the SS300 and the ground bus in the breaker panel (ground/neutral bus in your panel) to safety ground the chassis of the inverter.

bobdog · September 2010

Re: neutral bonding issues SS 300 inverter

dwh wrote: »

Well...

Really the grounds should be into one bus and the neutrals into another. In the main breaker panel you would then bond the neutral bus to the ground, either by bonding it to the metal box itself, or using a jumper over to the ground bus.

You can get away with what you did on a main breaker box, but if you were wiring a sub-panel it would be wrong to run the neutrals and grounds both into the same bus. (Wrong to bond neutral to ground in a sub-panel.)

As for the bare ground wire in the romex from the SS300 - that should connect to the "earth ground" terminal on the SS300 and the ground bus in the breaker panel (ground/neutral bus in your panel) to safety ground the chassis of the inverter.

I had intended to seperate the neutrals from the bare/ground wires at the main panel, but the panel only has one bus bar, so I combined them. I realize this would not be the case for a sub panel but I only have this one main.

Thanks for the advice on the bare/ground wire coming out of the ss300. After looking back at Tony's picture, it appears as though that is what he did.

Thanks to all the responders. It was all helpful.

Tim

bryanl · September 2010

Re: neutral bonding issues SS 300 inverter

The AC panel becomes your service entrance. That should be the only point where your neutral, your chassis ground, and your earth ground are bonded together. Everywhere else in your system these three parts of the electrical system should be kept separate.

The chassis ground, the bare wire or the green terminal, should always be used to make sure all electrical chassis points are connected together to a common reference.

A small inverter or generator that is single phase, under 5kw, and generally uses plugs does not have a neutral as the code defines it. It may have a 'grounded terminal' but the term neutral is defined for the neutral point in the middle of a split phase AC system.

Whether your inverter allows for a grounded terminal, where one side of its power leads is connected or bonded to the chassis ground, depends upon its circuitry. Check the manual. Generally, for low power single phase sources, the power leads can be left isolated and there is no need to bond one side or the other to either chassis or earth grounds.

If your system gets a bit more complicated with more than just one AC power source, then your panel becomes a sub that is fed by a transfer switch and its bonding between chassis, earth and 'neutral' removed. The main service entrance for each power source feeds the transfer switch which will then manage connections between power leads and grounding as appropriate for the source.

bobdog · September 2010

Re: neutral bonding issues SS 300 inverter

bryanl wrote: »

...Whether your inverter allows for a grounded terminal, where one side of its power leads is connected or bonded to the chassis ground, depends upon its circuitry. Check the manual. Generally, for low power single phase sources, the power leads can be left isolated and there is no need to bond one side or the other to either chassis or earth grounds.

The Suresine manual states on page 7, that the neutral is define by the grounded leg, and thus either wire can be the neutral as long as it is grounded. So I think grounding the white wire in the service panel defined that as the neutral inside the Suresine. But running a wire from the same leg to the earth ground on the battery side causes this as well. The one issue I wonder about is this. If I run a wire from the AC side around to the DC ground, am I at risk of crossing up AC with DC power?

bryanl wrote: »

If your system gets a bit more complicated with more than just one AC power source, then your panel becomes a sub that is fed by a transfer switch and its bonding between chassis, earth and 'neutral' removed. The main service entrance for each power source feeds the transfer switch which will then manage connections between power leads and grounding as appropriate for the source.

That leads to a quandary about my generator and when I get to the point of installing a transfer switch so I can use either battery/inverter AC or generator AC. The generator has a bonded neutral and I've been instructed by the technicians that I will need to disconnect that bond before plugging it into the system. I assume that is because they believe my system neutral is already bonded to ground at the service panel.

However, if I were to leave the generator neutral bonded, AND disconnect the neutral bonding in the service panel then I would be using the bonded neutral from the generator. At that point my service panel becomes a sub panel. Right?

But, the kicker is what about the neutral on the inverter? How would it get bonded? Maybe by running a wire set-up like Tony's?

Hmmm....

Tim

dwh · September 2010

Re: neutral bonding issues SS 300 inverter

Sort of depends on if you have a ground rod and the whole system is actually grounded to the planet Earth.

If you do, and the ground rod is connected to the breaker box, then you should leave the bonding in the panel, and unbond at the inverter and generator.

bryanl · September 2010

Re: neutral bonding issues SS 300 inverter

An earth ground is usually a good idea in a fixed installation.

As for the neutral to chassis ground bonding, keep in mind that this isn't really an issue for low power portable systems like plug in gensets.

If a neutral to chassis ground bond exists, that is the point where the earth ground should also attach and would be your 'service entrance' - after that, it's sub panels all the way down ... !

See Watch out for supposed experts for some links about this topic.

The thing is that, if you are talking about systems of 5 kW or less, the key issues are proper isolation between power leads and chassis and proper earth grounding for lightning protection, static dissipation, and noise reduction. The induced currents problem and grid related phenomena really aren't much of a concern.

BB. · September 2010

Re: neutral bonding issues SS 300 inverter

I am of mixed feelings regarding floating the generator Hot/Neutral vs the safety ground (ignoring the ground rod which is not practical or really needed for a portable installation (unless you have lightning in the area--then even getting in and out of a car can be an issue at the moment of a strike)...

A truly isolated generator (or inverter) output is pretty safe. You can touch any one wire and not get a shock.

However, the problem/issue (for me) is if you have a short somewhere in the system and you have metal electrical boxes/appliances. Now one of the generator/inverters wires is ground referenced. That one wire now becomes the "neutral" and the other connection (or connections if this is a 120/240 VAC split phase power source) is hot with respect to ground. So, your system is no longer "touch safe" and may or may not have the neutral wire "shorted" to ground... So the polarity of of the hot/neutral/hot may not be what is wanted/expected.

For some large ship systems I have seen (again, not an expert)--They use a set of lights that show the two 120 VAC power output leads are actually floating and if one lead gets shorted to ground, one light goes out and the other goes to full intensity (and probably sets an alarm).

The idea of having Ground and Neutral tied together even off-grid can be a very good thing for a distributed installation with metal boxes/breaker boxes. You have a solid ground/neutral bond, and if there is ever a hot to metal box short, it will kick off a breaker and turn off the affected circuit. This also prevents you have 240 VAC with respect to ground (if one hot wire of a split phase system gets shorted to ground).

So, in the end, with the grounded neutral you have an "automated safety" system (or in the ship, a true monitoring system) to find unintentional connections that can energize metal or leads to hazardous voltages.

And, if this trailer ever get connected to shore power, you do not have a unintentional short between hot and ground that will be "discovered" when shore power is made (and the Neutral / Ground bonding is done by the shore power connection to the RV).

So, I don't know if it is standard for an RV wired for generator/shore power has, as part of the transfer switch, a Neutral/Ground bond connection as part of the transfer switch (N/G bond when off ground, N/G connection open when on shore power)--But for the couple wiring diagrams where that was done (that I saw)--it sure made sense to me from an "ultimate safety" point of view.

And the above issues are why double insulated appliances/designs (modern appliances with only a two blade plug instead of the two blade with ground connection) always made sense to me... It removed a whole bunch of ground / neutral and possible ground current issues for system designs.

-Bill

bryanl · September 2010

Re: neutral bonding issues SS 300 inverter

re: "I am of mixed feelings regarding floating the generator Hot/Neutral vs the safety ground" -- you're not alone.

On rv.net there was a lengthy discussion on this topic. The 'stanford professor' and Grizzy had a very good discussion on the issues you raised with the professor pushing faults and Grizzy describing why the code came to be as it is.

One of the big conceptual problems is one I see here: you don't have a neutral in a single phase system. If you have a split phase 240v system then you do have a neutral and it should be connected to chassis ground. But with a single phase 110v system, floating power leads do not present the scenario hypothesized.

If there is a wiring fault in an isolated leads system, it will only define the 'neutral' side. Another fault will then be needed to create a safety hazard.

Another big issue, besides the definition of a neutral lead, is that of separately derived system. When a portable system has connections to the grid, the rules are different. That gets into your bit about discovering faults by plugging in an RV.

The key, I think, is that the electrical code is not a willey nilley whim of some turkey in a bureaucrat's office. It has come about through lessons learned the hard way. If you don't understand why it specifies things the way it does, then it might be best to take that as describing something you need to know more about. Of course, there are the problems of perceptions (maybe you don't understand what it is saying) or errors (reading the wrong chapter) - been there, done that! - but otherwise, it is a caution to make sure you really really know what you are doing when you think you know better.

BB. · September 2010

Re: neutral bonding issues SS 300 inverter

There is one practical reason to define a "neutral" circuit with a ground reference... That is for the few appliances that actually need the ground reference to work properly.

The only two types I have run across that need this are Florescent Tube Fixtures and some automatic ignition systems for stoves/water heaters with spark type ignitors.

Many florescent tube fixtures need the grounded sheet metal to help them start (the initial "arc"). And for the stove "spark type" ignitors, they use the grounded reference to detect when there is a fire (initial lighting and if the fire blows out) and then start the sparking cycle (that we found out when it turned out the contractor wired the Hot/Neutral backwards on our stove during a remodel). Without the ground reference, you may have inconsistent operation.

-Bill

PS: There was one other appliance I ran across where it made a difference--This was a very old tube type dual power radio (AC power and battery). It turned out the external wire antenna was referenced to the AC power--Depending on how you plugged the unpolarized plug into the outlet, you got an energized antenna... The details are fuzzy (I discovered this as a young kid decades ago)--But older equipment/house wiring can "surprise" you.

Also, found out a couple decades later that a friend's dad had wired his entire backyard shed with fuses all in the neutral side of the line... Don't know how many times we took our lives into our hands when we were playing with extension cords/appliances/motors...

Also, same friend discovered that his father had wired his (then new) home with recalled breaker panels that were ripped out of housing track because they were free. Caused my friend hours of fun and $$$ to pull and replace the 50+ year old panels from his 20 year old home he inherited.

Don't take anything for granted when working with old devices and systems.

bryanl · September 2010

Re: neutral bonding issues SS 300 inverter

There is one practical reason to define a "neutral" circuit with a ground reference... That is for the few appliances that actually need the ground reference to work properly.
...
Don't take anything for granted when working with old devices and systems.

I think this is getting rather far afield and just illustrates that it is possible to find a rationalization for anything if one digs deep enough.

The caveat or caution about backwards compatibility is a good one as it is always a concern in a changing technological environment. But the issue should not be to abrogate modern standards to accommodate non-compliant stuff but rather to upgrade that stuff so it is in compliance with modern thoughts about safety.

It is also a good idea, I think, to work towards understanding and implementing current ideas about safety rather than spend the effort on reasons to bypass them.

neutral bonding issues SS 300 inverter

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