Quick Grounding Question

porch13

Just ordered my batteries and will be commissioning my new system soon.  My question is....can I bond the various ground wires (negative side of the bank, A/C side of the Outback FlexPower, etc.) together and run one wire out to the main ground rod for the cabin, or is it better to run each individual ground wire out there?

SilverB

You would bond all wires then run one OVERSIZED ground wire out to your grounding rod/plate, as long as your talking about the AC ground, and not the ac neutral.

porch13

Thank you, @SilverB.  Correct, just the various grounds.  Although....the neutral is bonded to ground within the A/C breaker box, but I believe that is correct, as long as there is only the one neutral/ground bond in the total system (if I'm reading the Outback FlexPower literature correctly.)

BB.

What people try to avoid is to have mutli point connections between your return cables (negative, neutral) and ground (green) wire.

We don't want current to flow through green wire ground wire/sheet metal/etc. and through the neutral (negative) cables.

With single point grounding, the current from your loads will never flow through the green wire ground unless there is a short.

A 6 AWG ground wire will take over 200 amps in a short circuit (cable lasts long enough to trip the breaker/fuse). For continuous power, only a fraction of that current (~55 to 75 amps NEC rated current).

And remember, AC power systems running at 120-240VAC vs your DC side which is running at ~12-48 volts... The DC side current is ~10x that vs the AC side... You don't want to mix your DC current onto your AC wiring/power system cabling. Plus DC sustains arcs much better than AC (you don't want a DC short to go through an AC breaker that is not rated for DC).

-Bill

mike95490

And some controller with GFI sensors, want to be the only common ground tie point, or they FAULT.

porch13

Hey @mike95490....I am installing the Outback FlexPower (FP1VFXR3648A) which has a built in GFDI.  Can you help me understand what you mean by it wanting to be the common ground tie point?  Not sure I'm following you.  Thanks!

mike95490

Ground Fault Sensor in a Charge Controller.
 Your manual will cover it, it may state that the only system ground must be in the controller box, or the wiring diagram sample they print, will show where the ground should be. Here's how one of my controllers states it:

DC GFP (Ground Fault Protection)
The Classic has internal ground fault protection (GFP) built in. Since 2008 the NEC requires a DC-GFP on all PV
systems in the USA. The built in DC-GFP eliminates the need to purchase and install an external DC-GFP. If the
internal grounding jumper is installed in a Classic, the battery negative and DC source negative must not be
connected to the system grounding conductor anywhere in the system. Grounding of these circuits will defeat the
GFP function. In a network with multiple Classics, all Classics must have the internal grounding jumper installed
and GFP enabled. The factory setting will make a DC negative to System Ground connection in the Classic charge
controller. The GFP function will need to be disabled for Positive ground or an ungrounded DC system.

And different one:

Do not connect the system negative conductor to this terminal. NEC requires the use of an external ground fault protection device (GFPD). The TriStar MPPT 150V does not have internal ground fault protection. The system electrical negative should be bonded through a GFPD to earth ground at one (and only one) location. The grounding point may be located in the solar circuit or the battery circuit.

Saggys

A grounding electrode (ground rod) only requires a #6awg solid copper wire to be connected to it. Connect the other end to your ground bus where you have your ground an neutral bonded. Only bond your neutral and ground at one single point.

mike95490

Ground Fault Sensor in a Charge Controller.
 Your manual will cover it, it may state that the only system ground must be in the controller box, or the wiring diagram sample they print, will show where the ground should be. Here's how 2 of my controllers states it:

DC GFP (Ground Fault Protection)
The xyz has internal ground fault protection (GFP) built in. Since 2008 the NEC requires a DC-GFP on all PV
systems in the USA. The built in DC-GFP eliminates the need to purchase and install an external DC-GFP. If the
internal grounding jumper is installed in a xyz , the battery negative and DC source negative must not be
connected to the system grounding conductor anywhere in the system. Grounding of these circuits will defeat the
GFP function. In a network with multiple xyzs , all xyzs must have the internal grounding jumper installed
and GFP enabled. The factory setting will make a DC negative to System Ground connection in the xyz charge
controller.
The GFP function will need to be disabled for Positive ground or an ungrounded DC system.

And different one:

Do not connect the system negative conductor to this terminal. NEC requires the use of an external ground fault protection device (GFPD). The TriStar MPPT 150V does not have internal ground fault protection. The system electrical negative should be bonded through a GFPD to earth ground at one (and only one) location. The grounding point may be located in the solar circuit or the battery circuit.

And there is the problematic issue, if the system senses a problem, it ends up disconnecting the safety ground.   ZAP !  I think they are fixing the NEC pretty soon.