New Building Ground Completed

[Tywais]

When one of our research buildings was built we installed a very good grounding system. It consisted of a 4 meter x 4 meter mesh and 3 meters underground. However, a new building was built next to it and the ground systems was ripped out. They put one small ground rod next to the building and it started having a problem as high levels of noise was showing up on some of our equipment. These are large research machines and need a solid earth ground to minimize loop and rf noise. One such system operates at 1 million volts and uses 10kW switching tubes to produce it through a HV step up transformer. At the end of the accelerator are very sensitive instrumentation at levels of nano amps, that's one amp preceded by 9 decimal places.

I decided to design a new ground for it and it consists of 4 3 meter rods spaced between 4-5 meters apart and interconnected with 90-100 square mm copper wire. The ground rods were high quality copper clad steel. Due to space, two went at the side of the building and two in front. To maximize life time and minimize the theft of the copper wire I had the wire and top of the rods put underground. Obviously in this case you can not use conventional grounding clamps as they will corrode underground. The technique I used, common in making UFER grounds by bonding copper to the internal building rebar, was Cadweld One-Shot appliances. This uses ceramic casing with holes in the side for the ground wire and a hole in the bottom which the ground rod sticks into. Then thermite, in this case powered iron with perhaps powered aluminum is poured into the cup and then covered with another piece of ceramic with a torch hole at the top.

A blow torch is put at the hole to ignite the thermite. This then melts down into the junction of the ground rod and wire and bonds them into one unit. The temperature is around 2500 degrees C. The rods and wire are then pushed into the ground for complete coverage. Photos below. BTW - 3 meter multiple rods were chosen as this is an industrial grade building with a 400 amp service.

One-Shot ceramic appliance

Thermite (powered iron)

Two rods in front of building before thermal welding

End cable termination

Final front (buried) and side runs. Could not bury the side cable due to concrete and time constraints.

[Tywais]

Here is a YouTube video showing the Cadweld one-shot method.

http://www.youtube.com/watch?v=Ah3c2ntULHI&feature=fvsr

[Tywais]

Cadweld appliances

This is the box of the Thai version.

[jbrain]

Why would copper clamps corrode underground? If so the rod itself would corrode also in my opinion.

[Tywais]

Why would copper clamps corrode underground? If so the rod itself would corrode also in my opinion.

The connection points from the clamp to the rod can become resistive over time. Copper oxides with contact with water. 3 meters of rod with a fairly thick copper cladding will take a very long time to corrode. Take a look at a standard, above ground, ground rod clamp. You can easily see the weakness if underground. Normally you would cap the top with PVC pipe or similar with this type.

[Tywais]

The traditional method of doing ground rods is pretty flaky, often isn't done right, and requires frequent inspections and touch-ups. The ground rods normally stick out above the ground, and use compression connectors to squeeze the ground wire for a "good" joint. Can you say "corrosion?" That exposed connection WILL deteriorate, no matter how much Penetrox you slop on it. And, since it needs to be inspected, you have to keep the connections above ground. Yuck!

With a couple little kids running around the yard, and with poor soil that needs lots of ground rods, I needed something better. Besides, I want to make QSOs, not spend time checking/cleaning ground connections. Enter exothermic welding.

CADweld basically melts a metal around the joint where the ground rod and wire meet. It's a molecular bond, which means no corrosion between the wire and rod. It's a solid joint, a blob of metal. All of my ground rods are buried, so there is nothing to see except from the base of the tower to where the wires go under ground. The copper will rot before the CADweld connection fails.

CadWell Experiences

[Tywais]

They have now sealed the two ground points next to the building with concrete.

[electau]

It should be pointed out that for most electrical installations ( not special purpose installations) all that is required irrespective of whether it is a MEN ( TN-C-S) or TT is one copper clad steel electrode with equipotential bonding with a compliant main earth conductor and PE conductors. It must be exposed to the weather and be accesible for the purposes of testing and inspection.

The main purpose of an earthing system is to provide a path for fault currents and auto disconnection in the event of an earth fault and to minimise the touch voltage to less than 50VAC.

The temperature of the cable insulation must not exceed (for most general purpose PVC cables) 70C ( TIS) under fault conditions.

The protective device if an MCB must trip within 0.4secs and if this can not be achieved RCD/RCBOs must be used.

[doglover]

Very nice. What is the cost for 1 Cadweld kit (Thai version)?

[Tywais]

Very nice. What is the cost for 1 Cadweld kit (Thai version)?

Surprisingly cheap actually at 200 Baht.