System grounding Magnum

HumMichael

I  slowly reading documents prior to converting my small array garage off grid to grid assisted system using magnum 48 inverter amd their panel.
The incoming AC is grounded at the main panel prior to the subpanel I am getting the 60amp from. 

Magnum manual states that if neutral and ground are bonded at the main panel, I must remove the neutral/ ground,  system bonding jumper, in magnum panel.

Can someone explain what this means?

Does it mean that neutral in the magnum panel must not be bonded to ground and I only run ground wires from both AC and DC to outside grounding rod separate from my house main panel's ground rod?

Please share some insight.

Sincerely,
Michael

Estragon

Ground should generally be bonded to neutral in one (and only one) place. This is commonly done in the main panel.

BB.

Many (some, most, all?) larger AC inverters (more than few kWatts in capacity) and larger gensets operate on the assumption (in North America) that they are the only source of AC power and it needs to be wired per North American Standards (i.e., grounded neutral at the main panel).

It gets confusing when you have multiple sources of AC power--Grid, inverter, genset, etc. And the definition of where the main panel is.

So, the larger units tend to have a wire/jumper from the "neutral" (white wire) to the frame/chassis of the device (inverter, genset, house main panel, etc.). The grounding is done for safety (the neutral is always at "zero volts" and does not have any fuses/breakers on it, anywhere in the system). If there is a short with an grounded neutral, it is possible for the neutral to become "hot" and electrocute somebody and/or over current and cause a fire.

Other reasons for grounded neutral--Usually nice for reducing damage from a lightning strike. And for a small class of devices (some florescent tube fixtures, automatic spark ignition for stoves and water heaters), the grounded devices work better (florescent fixtures start quicker/better, flame sensing of ignitors work correctly).

So--You have to go inside the inverters, gensets, and such, find the "jumper" or "bonding screw" and disconnect all but one of the ground to neutral connections. Otherwise, it is possible to get "circulating" currents back through parallel ground and neutral connections and have some electrical problems or possible overheated white/green wires somewhere.

In some cases, like an RV that can run both from AC plug to house/campsite and run off of inverter+genset when dry camping, the wiring connections for bonding are even more complex--People have to sometimes put a relay in place to choose the "correct" location for AC neutral bonding. Some AC inverters with AC input connections will manage the AC ground bond for you with their own internal AC relay.

-Bill

HumMichael

Thank you Estragon and BB.
As I was studying about what neutral/ground bonding I learned a few things as you guys described.

I have to open my main? to make sure that neutral/ground are in fact bonded together, if not then I will call an electrician.

If properly bonded, I will make sure to keep my subpanels, inverters, etc not to have any bonding at all including removing the green screws prevent chasis bonding.

I found an interesting video that states that small generators in fact have a floating neutral and if you are connecting that as AC source, you do not have a lightning protection. There was a gizmo that by plugging it into one of the generator's outlet, it temporarily created neutral ground bonding not resulting in a fault.

Sincerely,
Michael

BB.

If you put an AC Voltmeter between ground (center pin in outlet, cold water pipe, etc.) and the two 120 VAC leads. One will read ~120 VAC and the other will (should) read less than 10 VAC (usually very close to zero).

If not, then either you are making the measurements wrong, or there is a wiring problem with the house.

All homes in the US have a Neutral+Ground bond somewhere (99%+ in the main panel). There are a few folks that have discovered that their homes were miss-wired (such as snow melting around their ground rod near the main panel outside the home).

Does not hurt to check with meter--But the chances that it is wrong is very very low.

Sub panels will frequently have a multi-function Neutral bus. If you look, the bus bar is mounted on plastic (floating), but there may be a screw location that can optionally tie the neutral bus to the metal case of the sub-panel (more modern devices--Older homes, who knows).

-Bill

HumMichael

BB. said:

Sub panels will frequently have a multi-function Neutral bus. If you look, the bus bar is mounted on plastic (floating), but there may be a screw location that can optionally tie the neutral bus to the metal case of the sub-panel (more modern devices--Older homes, who knows).

-Bill

That screw should be removed right?
Thanks for your explanation.

Sincerely
Michael

BB.

If you are installing a new sub panel, then the neutral to ground bonding screw should be removed or stored in the not grounding position.

-Bill

HumMichael

BB. said:

If you put an AC Voltmeter between ground (center pin in outlet, cold water pipe, etc.) and the two 120 VAC leads. One will read ~120 VAC and the other will (should) read less than 10 VAC (usually very close to zero)
Bill
When you say this test, I am checking at the main not a sub panel?

Thanks
Sincerely
Michael

Estragon

I'm a bit confused. What exactly do you mean by converting your small array garage off-grid to grid assisted? What do you have for power sources and loads now, and what are you adding?

HumMichael

Estragon said:

I'm a bit confused. What exactly do you mean by converting your small array garage off-grid to grid assisted? What do you have for power sources and loads now, and what are you adding?

Right now I am feeding electrical needs in my garage/mancave using 12v solar setup. I am planning to convert to Magnum 48v system which I will feed the original 60 amp coming in as the AC input to the magnum panel/ inverter. Once this is successful, I plan to have 10k system using two Mangum 4448 grid assisted to yhe main house using a critical panel distribution.
Thanks
Sincerely
Michael

Estragon

So if I understand this, the "original 60a" is an AC sub-panel fed from a main AC service entrance panel in the house. I assume there is a ground tied to neutral in the main panel, and not in the sub-panel. Can you check for voltage between neutral and ground in the sub-panel?

You don't say what loads are being powered by the 12v system. Are there/will there be battery storage?

Are you looking at a grid tied inverter?