Earthing the mounting

*

To vent my frustration with my first try at FireCapture I banged a 1.5m [60"] length of 20mm [3/4"OD] galvanized steel, water pipe into the ground. I positioned it at the foot of one of my 14' tall, 4"x4" pier legs. I reasoned that if the ground is still damp under the gravel, inside the building. Then it will still provide a good earth but will be protected from lightning. Rain falling outside the observatory building helps to keep the whole area under the building damp. The 2" of "pea gravel" keeps things clean, dry and tidy on the surface.

I had screwed on a steel end cap before going to work on the pipe with the lump hammer. This was to protect the threaded end of the pipe from the hefty hammer blows. It took only ten minutes to sink the pipe until only a couple of inches remained visible. The cap unscrewed easily enough afterwards. So I put it in the lathe to bore a 12mm hole centrally in the top. 

The hex from a 12mm bolt head was turned to a slight taper to clear the inner diameter of the pipe. Passing the bolt through the hole in the cap will act as a cable clamp with a big brass washer under the nut to increase the contact area. The tapered bolt head will jam in the pipe as the cap is screwed on hard.  Further increasing the conducting surface area over and above the tightened threads between the cap and the pipe.

The pipe and fittings are galvanized inside and out so corrosion will be very slow. I suppose I could grease or oil the threads to slow the build up of rust. An outer, screw clamp will ensure the earth cable enjoys even better conduction to the earth pipe.

The pipe went down so easily I am tempted to buy a longer length of 20mm OD [14mm bore] standard water pipe. This will help to increase the earth "rod's" surface area. Reaching even deeper into the wet, clay soil below the two feet of still damp, self compacting sand and gravel. Which I had used to raise the ground surface for the building to match the level of the parking area in front of it. 

It seems I am much better at such simple mechanical tasks than working with new imaging software! Or perhaps I was just very lucky with my exact siting of the earthing rod? Interestingly, my cheapo multi-meter measured the same 60V potential on the mounting when I connected between the temporary earth rod [pipe] and the mounting. 

In the interests of safety I have decided to order a "proper" earth rod 2m [6'6"] long x 14mm [~0.55" or 35/64" Ø.] Plus a protective metal top cap with a serious, internal, cable clamp. This was the kit I fitted years ago to my Hifi specific 3-pin sockets indoors. To kill the hum experienced on the normally 2-pin sockets in Danish homes.

6 meters of 6mm^2 green/yellow earthing specific cable will connect the mounting metalwork to the spike inside the building. I will clip the cable to the timber, pier leg to keep things tidy and to avoid shorting out the pier's physical isolation from the supporting building. None of this earthing stuff seems to be available at ordinary Danish, builder's merchants. So I had to buy it all online.

*