[TowerTalk] Clamp on ground resistance meter

[Grant Saviers]

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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