Ground Block – Forest of Tabs

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The electrical part of building an aeroplane is challenging, not least because you are cast adrift with very little “official” advice from the kit manufacturer.

You are the “Design Authority” … gulp!

Where to ground all the electrical devices is another example … some say through the airframe, or avionics via a separate ground point, or everything back to a single point.

Eventually you have to make a decision, so mine was to provide a single point for all grounds.

I decided to mount it on the aft face of the front right upper firewall, which provides an ideal short link to the battery negative terminal on the forward side of the firewall. Having been planning the whole electrical system it quickly became evident that you need a lot of grounding points, as other people have found.

Over here in the UK there is very little choice of commercially available ground blocks, so I made my own. The advantage of this was that I could size it to fit the planned location.

I purchased some copper plate, nylon sheet and …


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… some neat 1/4″ tabs with an integral Copper Pop Rivet to attach them to the copper.

These should enable a trouble free attachment, combined with minimal electrical resistance.


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Of course this means that I had to work out a way to provide space for the pop rivet shop heads against the firewall … hence the nylon sheet.

I chose Nylon 6.6 which has a melting point of 260ºC, so should be OK against the firewall.

Also it means that the copper will not actually touch the firewall stainless steel, avoiding corrosion issues.


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Once all the holes were drilled, it was a quick job to rivet the tabs in place.


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It resulted in very firmly attached tabs!


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The block is attached with 2 bolts. The main one is a large brass bolt, where the braid link will connect to the battery on the front of the firewall.


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If you are planning a Garmin avionics fit, then the lower nutplate shown by the left arrow is not needed. So I drilled through this one (rather than removing completely), and made enough clearance in the nylon block the other side to clear the nutplate itself.

So the other bolt is just an AN3.

The right arrow shows where the brass bolt emerges, well placed for the battery terminal.


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View of attachment points on the aft firewall face.


I made some little brackets to support plastic bushes to route the ground wires onto the “Forest of Tabs” from the avionics bay.

I emulated the Vans design … this means I can cut a slot in the bushes, and then for future access I can easily remove wires and work on them through the Avionics Access Panels in the forward top skin.

Hopefully because I’ve done this, I’ll never have to remove them! We’ll see.

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