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Another earthing question: A slightly more complicated set-up


Jakes
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Guys

 

Our system is completely off-grid. We are in the Karoo, it's (extremely) rocky.

 

The 15 (250W) panels are a couple of meters away from the small dedicated building that houses the charge controller (100A M/C), inverter (5kW M/C), batteries (12 Narada REXC200's) and generator.

The inverter supplies AC to our house, about 80m away.

It also supplies another building (a shop/restaurant) that is also about 80m away, in a different direction.

 

I'll appreciate your thoughts on the earthing of the whole system.

 

  • I was planning to earth the frame of each panel with an earth clip, running to an earth spike in the ground next to the array.
  • There's a 2-core plus earth cable running from the inverter to each of the 2 buildings. I was thinking of putting an earth spike where the power enters each building and connecting the building earth there.
  • MicroCare wants the earth and neutral bridged at the inverter. I'll do that.
  • I've also planned to put an earth spike at the servitude building and connecting the inverter earth there.

 

I'll appreciate your comments on the following:

  • Do you agree with the 4 earth spikes?
  • Will you connect all the earths together? If I should do so, should I also connect the earth of the solar panel frames to the rest of the earth "network".
  • The spike at the panels and the one at the servitude room will be about 8m apart. Would you rather see me use a single earth spike in stead of the 2?
  • Earthing anything else on the DC side seems controversial, but I'd like to follow the correct (legal?) route.
  • Anything else that I should do?

 

Thanks a mill.

 

J.

 

 

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  • 3 weeks later...

Hi Eugene.

 

I spoke to the electrician who did the installation of the 2 buildings at our place. (He can also sign off my solar installation, although he didn't do any work on it).

 

He preferred a spike at the solar panels, a spike at the battery/inverter building, and one each at the house and the shop. I used 1.2m spikes.

 

Somehow I was reluctant to link the earth from the panel frames to the rest of the system, but I linked all the other earth wires

 

He spoke about a tester of sorts to test the quality of the earths, but didn't look like he thought it was necessary.

 

What would you have done?

 

Thanks.

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@Jakes

 

The earth continuity must be 0.2 Ohm, test is done with a 500V meggar.

As many earth spikes as possible to achieve 10 Ohms, test is done with a earth spike tester.

These tests have to be done to complete the COC.

PV panel frames must be connected to the common earth (equipotential bonding).

Yingli installation pdf recommends that the negative also be connected to ground.

 

 

post-982-0-29914100-1442303807_thumb.png

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I would be very careful with grouding the negative on the panel. The current sensor of the mppt controller is often in the negative line, and if your inverter also grounds battery negative to the case (and you have the case tied to ground), or if negative is floating (which appears to be the case on my Victron), you could 1) end up with a parallel resistor across the current sensor of the mppt controller or 2) create interesting paths for currents to go...

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