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Old 11-16-2012, 11:12 AM   #1
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Installing earth ground


Hello

I have some questions regarding the installation of a grounding rod to provide an earth ground to my cabins electrical system.

The cabin is wired with 4 AC circuits all joined in a breaker panel. The breaker panel is located in the loft of the cabin which is approx. 25 ft from the earth below.

I want to attach the breaker panel to an earth grounded grounding rod. My idea to do so is as follows:

Install a grounding rod in close proximity to the cabin and below the breaker panel location into the earth below.

Attach the copper grounding wire properly to the ground rod and encase the wire within pvc or similar conduit pipe that will run upward along the outside wall of the cabin into the loft utility room where the panel is located.

In addition to the breaker panel itself, there are other components that I need to earth ground as well.

1. Is it okay to connect the main ground wire that is connected to the ground rod to some type of bus bar that all necessary grounds can then connect to? If so, any suggestions on how to approach this, where and how to install a bus bar for the grounds to connect to?

2. Also, is my idea to run the ground wire in pvc conduit along the outside wall of cabin a good idea or what do you suggest since it is up so high?


I will note, the additional components that need grounded involve an off grid solar system which include the solar panel frames, the inverter, and the battery bank.

Any ideas suggestions thoughts etc. would be great

Thanks for your time

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Old 11-16-2012, 11:58 AM   #2
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Installing earth ground


Run the wire (#6 copper) as a grounding electrode conductor from the ground rod up to the panel where the first whole-house utility power disconnect switch is located, and connect it to the bus bar or terminal strip where all the neutral wires are connected.

You will need two 8' ground rods at least 6 feet apart.

Use PVC conduit or Wiremold (tm) or other protection for the GEC where it might be subject to physical damage, like within 5 feet of ground level.

If there are not enough spaces on the bus bar in the panel with the main disconnect switch or breaker for all the neutral conductors (only one per space) and all the branch circuit ground wires (equipment grounding conductors) then you will need another bus bar for EGCs that don't fit.

For subpanels (panels downstream of the main disconnect switch's panel) all the EGCs must be on a separate bus bar from the neutrals. Here the bus bar for the neutrals must be on plastic standoffs from the metal panel with no connection to the ground bus bar.

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Last edited by AllanJ; 11-16-2012 at 12:05 PM.
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Old 11-16-2012, 12:12 PM   #3
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Installing earth ground


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Run the wire (#6 copper) as a grounding electrode conductor from the ground rod up to the panel where the first whole-house utility power disconnect switch is located, and connect it to the bus bar or terminal strip where all the neutral wires are connected.

You will need two 8' ground rods at least 6 feet apart.

Use PVC conduit or Wiremold (tm) or other protection for the GEC where it might be subject to physical damage, like within 5 feet of ground level.

If there are not enough spaces on the bus bar in the panel with the main disconnect switch or breaker for all the neutral conductors (only one per space) and all the branch circuit ground wires (equipment grounding conductors) then you will need another bus bar for EGCs that don't fit.

For subpanels (panels downstream of the main disconnect switch's panel) all the EGCs must be on a separate bus bar from the neutrals. Here the bus bar for the neutrals must be on plastic standoffs from the metal panel with no connection to the ground bus bar.
Thanks!

I will note that this is an off-grid system where the only power supply to the main panel comes from an inverter that converts my dc bank to ac.

Because of the type of inverter I have, the breaker panel contains no neutral ground bond. Does this change your suggestion at all?

My main goal is to ground the only breaker panel that is in the system, which consists of the 4 circuits. Therefore I would connect the #6 wire to the bus bar in my panel that has all the neutral wires connected as well (if there is room)?

If I wanted to earth ground my solar panel frame, my inverter, etc.. would the ground wire from those connect to that same bus bar?
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Old 11-16-2012, 01:00 PM   #4
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Installing earth ground


What type (make & model) of inverter do you have ?
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Old 11-16-2012, 02:18 PM   #5
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What type (make & model) of inverter do you have ?
Cobra CP1575 1500 Watt modified sine wave type
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Old 11-16-2012, 03:08 PM   #6
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Installing earth ground


That is a vehicle inverter, not a home system inverter.

I would not wire it into any house or cabin system. Just use extension cords from the GFCI outlets provided. Or, get another inverter that is made to be connected to a home system.

Why don't you connect it to a battery and measure the voltage. You will most likely find 60 volts on both the hot and "neutral" as measured to ground.
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Old 11-16-2012, 05:20 PM   #7
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Installing earth ground


An electrical system originally built to be off grid and fed by a solar power system or a generator or a car inverter usually has as its master on-off switch that in the power source system or module. In other words this switch is the first main disconnect. In this case neutral and ground are bonded together only in that power source and the grounding electrode conductor should be fastened to the neutral bus there.

For the panel without the neutral ground bond (technically it's a subpanel) it is permissible to run a GEC from it to the same or different ground rods as those the first disconnect's panel is run to. Connect this GEC to the ground bus bar. The first panel (feed wise) in a given building, say a subpanel in a barn, must have its own GEC and ground rods connected to its ground bus.

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Why don't you connect it to a battery and measure the voltage. You will most likely find 60 volts on both the hot and "neutral" as measured to ground.
A power source for 120 volt or 120/240 volt household power should not do this. It should be 120 volts hot to ground and 0 volts neutral to ground. Bonding neutral to ground in the source module should assure the 0 volts neutral to ground (and not burn out anything).
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Last edited by AllanJ; 11-16-2012 at 05:29 PM.
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Old 11-16-2012, 06:30 PM   #8
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Installing earth ground


A PV inverter to be wired into a home should be UL 1741, whether it is on or off grid.
The inverter in question is almost certainly a UL 458.
UL 458 does not require a neutral ground bond.

Here is what Xantrex has to say on the subject from their FAQ's

"Your inverter is designed to have loads plugged directly into it and not be permanently connected to an AC distribution system. The fact that the inverter is not a permanent installation means the US NEC (United States National Electrical Code) doesn't apply, and the NEC is the main place where the requirement resides for single-phase 120Vac or 240Vac systems to have neutral bonded to earth. The US standard for inverters of this sort, UL458, does not have a requirement for a bonded neutral on the output of inverters.
Regarding the voltage that the you are measuring, the ground does not float halfway, rather the neutral is not at 0 volts. The grounding is correct, in that loads plugged in will have their chassis held at the same ground potential as the chassis of the inverter, but the neutral has approximately 60V on it instead of the usual 0V. The impact of that is minimal, since wiring and equipment connected to the neutral side of the circuit are required by safety standards to be treated as if they were at 120Vac. This is because there are many receptacles that are wired backwards or 2-prong plugs that are not polarized. As a result the 60V neutral is not accessible to the user, and any shock hazard presented is mitigated by lack of access.
The main safety agencies, CSA, UL, and ETL, have all approved inverters with this half-voltage on the neutral scheme, and the manuals contain warnings not to AC hardwire any of these inverters."
(bold added)

Unfortunately, the Cobra manual is not clear on this subject. (One of the worst manuals I've seen) But from the construction of it, I am fairly certain it is a half voltage scheme inverter. A test will tell.

Last edited by Oso954; 11-16-2012 at 06:37 PM.
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Old 11-16-2012, 09:57 PM   #9
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Installing earth ground


It is entirely possible to have 120 volt AC produced in a fashion where neither of the two current carrying conductors used to provide the 120 volts output is "grounded." And where there is a "center tap" or other part of the inverter circuit, call it the internal neutral, that measures 60 volts to each of the aforementioned current carrying conductors.

The question remains, is the internal neutral bonded to the chassis? If so then it is accessible, or rather if the internal neutral is not accessible then it is not bonded to the chassis.

If the internal neutral is not bonded to the chassis then we can ignore its presence.

To prove whether the internal neutral (or something else) is bonded to the inverter chassis we measure voltage from the chassis to each of the current carrying conductors while a small 120 volt incandescent lamp (25 watts or so) is connected between the meter probes. Should in both cases we measure zero volts then nothing is bonded to the chassis.
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Old 11-18-2012, 05:29 PM   #10
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Installing earth ground


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Originally Posted by AllanJ View Post
It is entirely possible to have 120 volt AC produced in a fashion where neither of the two current carrying conductors used to provide the 120 volts output is "grounded." And where there is a "center tap" or other part of the inverter circuit, call it the internal neutral, that measures 60 volts to each of the aforementioned current carrying conductors.

The question remains, is the internal neutral bonded to the chassis? If so then it is accessible, or rather if the internal neutral is not accessible then it is not bonded to the chassis.

If the internal neutral is not bonded to the chassis then we can ignore its presence.

To prove whether the internal neutral (or something else) is bonded to the inverter chassis we measure voltage from the chassis to each of the current carrying conductors while a small 120 volt incandescent lamp (25 watts or so) is connected between the meter probes. Should in both cases we measure zero volts then nothing is bonded to the chassis.

Thanks again guys for all the info.

In regards to the inverter, I intend to upgrade to the following inverter from what I currently have.

http://www.morningstarcorp.com/en/sure-sine

With that said, the data sheet shows that it has an "earth ground" terminal to attach to.

The inverter would connect to my battery bank and then would wire into my current breaker panel, which as you said, is technically a "sub panel" that has breakers for the 4 circuits that run throughout the cabin. Additionally, this sub panel has no neutral ground bond.

I also have a charge controller in the system which is the one below:

http://www.morningstarcorp.com/en/sunsavermppt

The operators manual of the charge controller states:

"NOTE: The SS-MPPT is a negative ground controller. Any
combination of negative connections can be earth
grounded as required. Grounding is recommended, but
not required for correct operation"


So my question remains about the grounding. Assume I did the following and let me know what you think

1. Run a #6 ground wire from at least (2) 8ft ground rods, up the side of my building and into the utility room in the loft.

2. Inside the utility room connect the #6 ground wire to a bus bar contained within some type of panel, box, or similar that will allow several ground wires to connect to. *suggestions welcome*

3. Connect the ground wire from the inverter to the bus bar
4. connect a ground wire from a negative terminal on the charge controller to the bus bar
5. Leave the sub panel un-grounded
6. Connect ground wire(s) to the 3 solar panel frames or negative terminals? and into the bus bar
7. Connect a ground wire from a negative terminal in my battery bank to the bus bar.

Does this sound right or am I totally off

Thanks again

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