Grounding

Grounding

Does a solar installation need to be grounded, short answer: YES.
Longer answer: It depends on the layout of the solar system.
Grounding solar makes sense, sometimes.

The howto, however is one with many different interpretations. First of all, grounding is no solution for lightning safety. The reason we ground is about safety. keeping one potential connectected to the ground makes sure that we can’t have floating voltages. Also it’s the best way of guiding static away from sensitive equipment.

The NEC has a few special chapters about grounding solar set-ups:
  • 690.41 – System Grounding
  • 690.42 – Point of System Grounding Connection
  • 690.43 – Equipment Grounding
  • 690.45 – Size of Equipment Grounding Conductors
  • 690.46 – Array Equipment Grounding Conductors
  • 690.47 – Grounding Electrode System
  • 690.48 – Continuity of Equipment Grounding Systems
  • 690.49 – Continuity of Photovoltaic Source and Output Circuit Grounded Conductors

These articles contain a lot of information and even if you are more experienced with electrical installations some things are hard to understand or to interpret. To stay at our tiny off grid topic and try to simplify it a bit, a brief summary will be listed. Please note that this is incomplete and if needed, find the whole article with the NEC or ask your local building inspector.

These articles mainly states that every PV power system above 50 Volts should be grounded. A good solution for tiny off grid solar will be a regular ground rod.
Exception: Systems complying with 690.35 (Ungrounded Photovoltaic Power Systems).

The DC circuit grounding connection shall be made at any single point on the PV (photovoltaic) output circuit.
Exception: Systems with a 690.5 ground-fault protection device.

Metal parts that don’t carry any current shall be grounded. For example PV-panels, metallic frames and enclosures. Bonding is allowed. The grounding conductors for the PV-array shall run with the circuit conductors of that array.

The size of grounding conductors shall be sized in accordance with table 250.122  The maximum amount of current from the PV-panel Isc (short circuit current) shall be used. The equipment grounding conductors shall be no smaller than 14 AWG. Equipment grounding conductors smaller than 6 AWG shall be protected from physical damage according to 250.120 (C).

The Grounding Electrode System is required for both AC (alternating Current) as well as DC (Direct Current) systems. The most obvious, a 8′ copper ground rod is always a good solution but the NEC 250.50 through 250.60 describes many alternatives, for example a metal underground water pipe.

A lot of solar systems have both DC- as well as AC-circuits and it’s allowed to use a bonding conductor to bond the DC grounding to the AC grounding system. The DC current in a solar setup is usually higher than the AC current. Multiple inverters can use one single electrode.

There are different requirements between AC- (NEC 250.66) and DC- (NEC 250.166) circuits regarding the size of the Grounding Electrode Conductor but a good quick guide is to never have it smaller than the largest conductor or smaller than 8 AWG copper (6 AWG aluminum) connected to the 8′ ground rod.

It is always best to have just one ground rod in the ground. Multiple ground-rods can co-exist but should always be connected to each other, if not there might be a large different in potential if lighting strikes close by, this can easily be 3000 Volts / feet apart. To prevent this from destroying parts of your installation the easiest way is to have 1 ground rod in your solar setup.

In a PDF we placed al the ground conductors to one ground rod, a good solution for (small) off grid solar set-ups. Before grounding the solar charger be very sure if the is a common negative or common positive controller. An simple Ohm-meter can give you the right answer.

In this example we grounded the following:

  • The metal frame of the PV-panel(s), if applicable since flex-panels have no frame.
  • The charge-controller, if it’s in a metal enclosure.
  • The DC/AC Inverter enclosure.
  • The minus of the battery.
  • The outlets.

 

Grounding does not protect from lightning contrary to general believe so please take some precautions to minimize the rist of mayor damage.

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