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kcmiller asked

Earthing of MPPT

I am a little confused by the MPPT 250/100 manual regarding earthing. I intend to run an earth cable from the frame of my solar array to an earth busbar in a combiner box which will be situated about 3 metres from my domestic distribution panel. The earth cable from the surge protection device will also be connected to the combiner box earth busbar. This busbar will then be connected to the main earth busbar in my domestic DB. This cable will pass within 30 cms of the earthing screw on the casing of the MPPT. Can I run the cable to this screw and continue on to the DB board? Is it really necessary to earth the casing of the MPPT? I would appreciate some advice/comments.

Grounding
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wkirby answered ·

You should definitely earth the heatsink of the MPPT.
The heatsink is an exposed metal part which could become live in the event of a fault within the MPPT or even an external fault causing this to become live.

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kcmiller answered ·

Thank you. That's clear. My confusion is with the "Grounding" section in the MPPT manual which states:

Ground the frame of the PV panels to reduce the impact of lightning.

Do not connect the solar charger to a grounded PV array. Only one ground connection is allowed, and this should be near the battery.

I am running an earthing cable from the PV frame to the earth busbar in my domestic DB (via a combiner box). As I said, this cable passes right past the MPPT so I wondered if I could run it to the MPPT and then continue on to the DB, putting them in series. Am I not then connecting the solar charger (MPPT) to a grounded PV array?

If I run a separate earth from the MPPT to the DB, don't they all finally become connected?

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ahtrimble avatar image ahtrimble commented ·
My understanding is this; 1) there is earth grounding for surge/lightening that takes the energy strike directly to the earth/ground, 2) equipment grounding that moves stray voltage or a fault in a piece of equipment such as the MPPT to grounding. And the two are not connected to pass through any energy.

Running #1 through or to a piece of equipment before it goes to earth/ground would send all that energy through the piece of equipment.

Just for safety sake...I keep surge protection at the arrays separate from any other grounding. Equipment grounding all goes to my AC busbar then to an earth ground.

And it is best that each PV has a ground lug and I use a 6AWG bare copper wire connecting them...then it goes to a dedicated earth ground...that also has a surge protection device on it.

Any earth ground connection on my system consists of 3 x 8' copper plated ground rods put into the earth and a 6AWg bonding them together. The 6AWG is also buried 12" deep in the earth as well.


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