Simple Earthing Question

solarnewzealand

Why do we need to ground Solar Panels? They have special mounting holes in the frame for a grounding so it would appear you can string them all together if you have more than one. Is it because of lighting or other weather effects such as rain causing a short circuit in the connectors or combiner boxers getting wet, or even Inverter/Charge control, or other equipment failure taking the least resistive path down an electrode into the earth? Or another scenario might be wire degradation or short circuit causing insulation to melt will ensure it goes through to the ground instead of your body for example? How do you size Grounding wires?

BB.

Re: Simple Earthing Question

You ground the metal frames of the solar panels, and metal mounts for two reasons.

One, if there is a short circuit between the wiring and the metal, the ground will go back to the battery (also grounded to the common earth/safety ground) and prevent the metal from becoming energized and shocking somebody.

The second is for static build up (insulated metal/antenna/etc.) can develop hundreds to thousands of volts from the earth's natural electric field (~100-300 volts per meter, much higher under a thunderstorm). And, of course, because of lightning strikes--Direct the energy down to the ground (ground rod/ground plate) and away from the interior of the home.

The US code is usually 6 awg minimum for a bare copper cable. It is both for electrical ground (short circuit) of "normal" home sized electrical circuits (around 600 amps is fusing current for 6 awg cable) and for physical strength (minimum unprotected buried cable is 6 awg--as I recall).

I read about a church (in Germany?) that had both ~6 AWG and ~8 AWG wiring for lightning grounds. As I recall, some of the 8 awg cables failed (fused) and none of the 6 AWG failed... So, that seems to be another good starting point. (I am not a lightning expert, and I have forgotten most of the little code I knew).

Then, there is the whole DC Array Grounding issue. Nominally, in the US/North America, we used ground referenced "return" / "neutral" wiring. When one side of a circuit is ground referenced, it makes things a bit cheaper (only need fuses/breakers on "hot" leads) and is good for safety grounding (you know that under normal circumstances, the neutral is always near zero volts, and the "hot" is only offset by 12/24/48/120/240/etc. VAC. Grounding a return also acts like a safety ground for "line crosses" (when a 12kV distribution line crosses a 120/240 VAC home drop--such as high wind, pole knocked down, etc.).

There is an issue with "arc faults" and DC current/solar panels... There have been fires caused by shorted wiring/failed connections in DC solar panel wiring. With solar panels, fusing the panel wiring does not pop fuses (panels naturally limit current and fuses/breakers will not catch a short)--And a failing in-line connector can arc--And DC current sustains arcs very nicely.

There are some interim and (probably) new code requirements that are aimed at reducing the chances of DC "Arc Faults" (such as arc detection circuit breakers).

This is actually a very complex discussion and there are some local requirements (grounding/bonding) and support equipment (such as backup gensets, DC battery grounding, Grid Tied Inverter grounding, etc.). Also, I have kind of changed my opinion on some of these grounding issues too.

Do you have a particular setup that you want to discuss? It is usually easier to talk specifics for your needs, vs the "whole" universe of electric codes across nations.

-Bill