�� . �� : http://www.naic.edu/~phil/td/grounding/tdgrounding.html
�� : Fri Apr 20 19:03:16 2012
�� : Mon Feb 4 03:05:55 2013
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�� : astro-ph

td grounding

Tiedown grounding

The tiedown cables are the path to ground when lightning hits the towers/platform. To isolate the tiedown equipment we have:

attached grounding cables to the tiedown cables about 10 feet above the jacks. The other end of these cables are buried in the ground.
The Huffman box with the tiedown electronics is mounted on wooden standoffs so that it is not grounded to the aluminum support structure.

A cable from the top of the Huffman box up to the ground cable attachment on the td cables should be the path to ground

The transformer providing 208 3 phase power is a delta configuration with the common not tied to earth ground at the transformer.
The 3 phase power from the 208 transformer passes through a breaker panel. We need to check the ground connections here
The motor and encoder cables are not supposed to have their shields connected to ground on the encoder,motor side.

Measuring resistance to ground.

I measured the resistance to ground from the Huffman box to the vertical aluminum support structure to the right of the phone.

date	td	all connected	(1): motor heater Unplugged	(2):motorCable1 and (1) (black power cable)	(3):motor cable2 and (2) (grey resolver cable)	(4) encoder cable out and (3)	Notes:
19apr12	12	2 ohms	108 ohms	(inf,70Kohm) (*1) 1.7VDc,6VAc	(inf,200Kohm) 3.4Dc,10VAc	(inf,2Mohm) (*1) 3.6VDc,10VAc	motor power off (emgStop) Huffman box powered. ground strap not connected.

(*1): reversing the dvm probes changes the measured resistance. This is probably because of the voltages.
19apr12:

ground strap was not connected.
With the motor cables out, but the heater ac connected, the resistance was 1.5Mohm.
Inside the breaker box, the 120Volts that goes to the motor must have it's common tied to ground.

120 ac volts receptacles from breaker box (outside the huffman box) probably have their common (from the transformer) tied to the 3rd pin ( earth ground) of plug. If something is plugged in that then grounds the 3rd pin, the common from the transformer will also have this as a ground. Currently the microphone and motor heater are plugged in.