neutral bonding quick check
bobdog Solar Expert Posts: 192 ✭✭
OK, since my generator has the neutral bonded to ground and the inverter has the same, I plan on not bonding the neutral in my service panel. Essentially it will be a sub-panel. The AC from each will run through a Iota 30r transfer switch.
Does this sound like a good idea?
Does this sound like a good idea?
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Interesting question. I've never worked with a transfer switch that wasn't built into the inverter; just never had the opportunity. Neutral is supposed to be connected to ground in only one place in your system. But since you have a transfer switch, you'd think that at any one time either the generator hot and neutral would be connected to your system or the inverter hot and neutral would be connected to your system but not both pairs at the same time. Looking at the online docs for the Iota 30r transfer switch, the neutral connections from both the generator and the inverter are normally open so it sounds like you're okay i.e. the neutral is switched too.
Do you have separate gounds (ground rod or whatever) for the inverter and the generator, or do you have just one main ground that goes to a common point and then from there to the generator and the inverter?
As you describe it, and as I understand things, you have two separate power sources that each provide the services of a 'service entrance' - the use of a transfer switch that switches all of the power leads to choose between them (neutral and all hots) sounds right.
The issue is likely to be the chassis to earth grounding bond. I'd think that a good earth ground at the transfer switch would be the thing to do.
The key is what code refers to as 'separately derived system' and the differences that implies. If the genset and inverter chassis grounds were kept isolated, they'd be separate and the code requirements a bit relaxed. If the chassis grounds were connected, they would not be separate and a few extra precautions might be required.
Im having the same issue, I contacted Xantrex and had minimal success in resolving my question, (Xantrex now farms out it tech questions to Snider eElectric, ) and my rep seemed a little unsure as to how to resolve the potential problem. It seems I can either disconnect the ground to neutral bond in the genset, leaving me no neutral to ground bond for any extention cords that I might plug in, or run a seprate ground rod and devert my 240 ground to it? Does any of this make sense? My rep was unsure if the Xantrex 6048's built in transfer switch would effectively seperate the two neutral to ground bonds.
Yes, that's fine. That configuration is the same as an RV setup.
The only difference is the ground rod at the panel, but that's okay since there would be one if the RV were plugged into shore power; neutral to ground bond at the shore power panel - gen and inverter hot/neutral not connected to sub-panel.
Double-check that neutral is not bonded to ground in the transfer switch. Shouldn't be, but verify anyway.
Lemme see if I can get this straight...
According to the XW6048 Installation guide:
"Grounding the AC System
Important: Place the Neutral-to-ground bond in a permanently installed AC distribution panel that is part of the system. This may be a main panel or a sub-panel."
(page 2-18 )
So, the neutral is not bonded to ground in the inverter - it depends on the neutral being bonded to ground somewhere else.
If the neutral is bonded to ground at the AC panel, then when the generator is connected to the AC panel by the 6048's transfer switch, any extension cords plugged into the generator would have neutral bonded to ground. In that case, the neutral/ground bond should be disconnected in the generator.
If the generator is running, but NOT connected to the AC panel by the 6048 transfer switch (AC panel being fed from grid), then neutral should be bonded to ground at the generator.
If the generator is rigged for auto-start by the 6048 in case of grid failure, then whenever the generator is running, it will be connected to the AC panel by the transfer switch, and the neutral will be bonded to ground. In which case, again, neutral should not be bonded to ground in the generator.
If the system is off-grid, and the 6048 is simply switching between inverter and generator, then again - the neutral to ground bond is at the AC panel and not in the inverter, and again, when the generator is running it will be connected to the AC panel and again, there should be no neutral/ground bond in the generator.
So, the question is; Is there any situation where the generator is running, but NOT connected to the AC panel by the 6048 transfer switch? That's the only situation where not having the neutral bonded to ground at the generator could be a problem.
Mine is an off grid setup, so I;m guessing the real question for me will be is there a situation where not haveing a neutral to ground bond at the generator could be damaging to me or my equiptment? considering that I will be hard wired to the AC2(generator in) bus bars in my XW E-Panel distribution box. Oh , and I do plan on installing the Xantrex remote gen start.
For off-grid hard-wired then whenever there is power to AC2 (generator is running), the 6048 should flip the transfer switch and connect AC2 to the AC out (and switch on the battery charger) - so there should be no bonding in the gen if there is a bond in the panel.
Note: This is just my opinion from reading the docs - I defer to the Mighty Guppy for an expert opinion.
So if I were to ground the inverter, transfer switch and the main panel (sub in this case) on one rod, and then ground the chassis of the generator 30' away on another rod, would that be considered isolated?
I planned on having separate rods about 30-50 feet from each other. Now I'm not sure.
you can use 2 separate rods if you tie them together with solid #6 or better bare copper wire buried at least a foot below the soil. that makes the ground one large ground and a bit of expense for the wire and connections for going to the ground rods.
I think what they mean by "isolated" is that you need to "break" the internal chassis to neutral grounds in the inverter and the gensets, and use the one neutral/ground bond in one panel (main or wherever). Now the "neutrals" are floating at the inverter and genset. And you have your neutral/ground bond in the breaker panel.
But--Your other alternative of inverter/genset switched neutrals with the transfer switch is fine too.
You don't want to have two grounds 30' apart that attach to related equipment (like your gen/house/inverter wiring).
As Niel said, run all the grounds to one place--and if you need more ground rods--run more cable from the "central ground rod" to the rest (in a "star shape" back to the central ground rod).
If you get a lightning strike (or even a problem with the neutral bonding on the utility pole)--the two separate ground rods will pick up the voltage difference (hundreds of volts or more) and bring it into the home--could cause all sorts of problems.
With all of the house grounds going to one central ground rod--you cannot get differential ground voltages into your home's grounding system.
re: "disconnect the ground to neutral bond in the genset, leaving me no neutral to ground bond for any extention cords that I might plug in, or run a seprate ground rod and devert my 240 ground to it?"
A red flag here is "240" - If your genset is 110v it has no 'neutral'. A 240 system split into 110v phases does have a neutral.
110v gensets of 5kw or less using plugs for power taps do not need to have one side of the power attached to the chassis ground. If they do, it is not a 'neutral ground bond' but rather a chassis connected power lead.
Portable equipment generally does not need to worry about earth grounding and can depend upon the chassis ground for safety concerns. Note that this is a completely separate issue from the neutral to chassis ground bonding issue.
The earth grounding issue in distributed power systems is its own can of interesting issues. A primary difficulty is the fact that the earth is usually a rather poor conductor so you need (as described above) to create your own 'ground plane' between those points attached to the earth. This gets into problems of circulating currents and alternate current paths creating hazardous voltages that become more important when currents increase (lightning is the extreme case). High currents not only emphasize resistance differences between paths but can also create interesting induced voltages. The idea is to minimize these.
To get good advice on these issues, you'll likely need someone with good experience wiring farms to code. Places like Mike Holt's forum and pages can be a good resource.
Just to throw a bit of "European" into the discussion
If I was in England on grid, I would predominantly be using PME, This is normally bonded at it`s incoming pole/ underground/ meter, It should only be bonded in one place, "bonded at principal source of supply" as it is known, The point being, if for any reason the N > E bond is broken , the supply will most likely be removed also.
Our problem is we have 2 "principal source of supply"s the Gen and the Inverters, So if you bond in one, It may be removed (eg,gen blows up) and you should not bond in both (earth loop problems) My solution being to bond at the neutral bus and check/ remove the internal gen bond ( most gens over "hobby" size will be internally bonded)
In Spain, they use mainly "TT" no N > Earth bonding at all, But lots of RCD`s or as we know them differentials, I am not a fan of it and have seen life threatening voltages in several places where the RCD does not go out due to poor earthing, On the bright side, If you do put your fingers in the wrong place, most of the time it is only about 117v conductor to earth/you
Have a good one
Edited to add, RV was mentioned, I do not know on other manufactures, But with outback, All but the "M" (mobile) series inverters the neutral is not switched and common, If you have neutral switching, The above go`s out the window :-) Please check you manual