last updated. 08sep16
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
- 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
- This cable has been disconnected for many months.
- The transformer providing 208 3 phase power is a delta
configuration with the common not tied to earth ground at the
- 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.
- A fluke meter was used
- the Huffman box door was open , but not touching the aluminum
(black power cable)
cable2 and (2)
(grey resolver cable)
encoder cable out and (3)
|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.
- 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
- Note:the 3rd pin (earth ground) has been cut on the power
power cable to the motor heater,.
160907: Before the hf arcing test:
- see pictures
of grounding clamp on td cable pictures on grounding
clamp on td cable
- the tiedown cables are painted. using an ohm meter, infinite
resistance 2 inches apart on the cable ...
- hope hagen removed the paint before he had the clamps put
- the corner adjusters used to shape the dish have 0 ohms
resistance between the plate and the 3 by 6 panels. so they
could be the connection point for grounding the td cable to the
- from dish to ground clamp on td cable (5 feet)
- from ground clamp to plastic box holding the limit switches ..
10 feet. So the rogowski coil cable from coild to
processing box will probably reach from the td ground clamp to a
place by the td jack where we can set the box.
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