I bought an inexpensive one on ebay and used it to measure my ground rod
field. It came with a calibration loop and I also made a cal loop with a
resistor and it checked ok. A pretty cool meter.
An important thing when measuring (and prior when designing/installing)
is to not make loops of grounding leads. Then the meter will measure
the wire resistances. A star layout to a single bonding point at the
entry panel and one at the tower is the best design for this and other
more important reasons. Then each lead can be measured against the
parallel resistance of the rest of the rods. Likewise each new rod can
be measured against the group.
I found the "average" 8' x 5/8" rod was about 60 ohms, that #2 (new
code) leads 15 to 20' long have enough surface area to contribute
significantly to lower resistance when buried about 6 inches. For my 9
rods I measured with dry soil - 7.9 ohms, wet soil - 5.3 ohms and after
a hard freeze (rare here) - 6.4 ohms. Computed by paralleling the
resistance of each the rods and its lead and measuring against a 630
square foot earth contact Ufer foundation. So, I think the intrinsic
error in this measuring strategy was low. Harger or Erico thermite
welds to rods.
The Motorola book specifies 5 ohms as the "commercial standard" and
elsewhere I've read that 10 ohms is the target for ham grounds.
Of course, ground field resistance is a proxy for inductance which is
the most important variable to minimize. "Lightning is an RF event."
Have fun!
Grant KZ1W
On 9/29/2019 11:51 AM, Julio Peralta via TowerTalk wrote:
Does anyone have any experience using a clamp on ground resistance meter?
I bought one to use to help with my grounding project but don't have any
experience using this type of meter. Any advice would be appreciated.
Julio, W4HY
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