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Grounding and your solar system


Wetkit
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Right, so you doing a solar system, but what is the correct and legal way to do your earthing???

 

So far I have looked, I came across 2 words, Equipment and System grounding.

 

Equipment Grounding:

This is standard practice where each metal part of your installation is grounded with a suitable conductor.

The common eathing point of your solar system is then connected to your main home earth.

According to law, each metal part on your PV installation must be earthed. This means each and every solar PV panel must have its own earth point.

It is not acceptable to just ground the mounting rails.

 

System Grounding:

Now here is where it becomes interesting. According to EU, USA, AUS and NZ laws, at least one of the DC conductors needs to be grounded as well.

What this means is that your negative coming from the PV array needs to be grounded and your negative DC on the batteries needs to be grounded.

 

I have done the Equipment grounding, but still too scared I blow something up to do the System grounding.

 

Anybody done this before?

What does our local regulations say?

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I agree, equipment earthing (or grounding, same thing different words) makes sense & is straightforward.

 

System grounding is about whether to earth one pole of a battery to an earth conductor or not.

As far as standby battery installations are concerned I prefer not to earth a pole neither on PV side or on battery side.

 

If you were to earth one pole, you are effectively creating a "first earth fault" which is fine. (nothing happens as there is no short-circuit return path created to the other pole.)

Problem arises if you accidentaly create the "second earth fault" i.e. when you accidentally earth the other pole.

If you install earthing protection then you may sometimes require one pole to be earthed.

 

There is nothing to be gained by earthing one pole of a DC system other than if you wish to use the earth/ground as a current return path.

 

Cars work that way: you attach the negative pole to the body of the car. (some older cars use the positive pole)

But in that case it is about saving conductors as you use the metal shell of a car as the negative conductor.

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The only precaution you have to take, is not to take your PV array's grounding to the same as your house grounding, Had this problem a few years ago.

 

PV array must have it's own grounding, DC negative (batteries) must have it's own grounding and the AC side must also have it's own grounding the rods must be a minimum of 3 meters apart.

 

If you don't to this a short-circuit can become very expensive.

 

Electricity always takes the easy path and before it goes to ground it blows up a few things  if it is on one earth rod.

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The image you've posted is for DC systems - where you distribute DC throughout the premises e.g. your home and all equipment / appliances run off DC. That is why the DC negative is grounded as well.  On AC installations the Negative is also grounded before going into the E/L unit - when there is a ground fault (current leaking from Negative OR Positive to ground), the E/L unit disconnects the power if the leaking current is more than the leakage rating of the E/L unit.

 

You should however not connect the DC Negative of the PV panels or the batteries to the system ground unless your inverter / charge controller installation manual clearly states that you may do so, otherwise you risk damaging the inverter / charge controller.

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  • 4 months later...

Hi, I was reading your inputs with interest and I would like to add this.

At present in ZA they are still formulating regulations. so in the interim I run my inverters thru a ready board with it own earth leakage.

they same as in the house.

I earth the inverter chassis to this as well.

Effectively the system now has its own earth leakage protection.

On the DC side, PV's and batteries, I only earth the PV frames to the earth in the house. This is purely for lightning protection.

also, depending on the inverter, the negative is being switched and is often the same point as neutral on the 220 side.

so to earth the DC negative you will effectively be causing the earth leakage to trip.

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