Molded carrying case 9v alkaline battery and calibration verification loop.
Ground rod resistance tester.
Unfortunately it seems many electrical professionals.
The clamp ground tester is clamped around one of the electrodes and then measures the resistance of the entire loop.
Using an earth electrode tester instead of a clamp on tester will take a lot more time and effort.
In areas where driving ground rods may be impractical the two point method can be used.
Measure grounding circuit performance without disrupting service.
This type of tester is usually available at hardware and home improvement stores as well as from online retailers.
You are correct that the nec states that if you use one ground rod that the resistance to ground must be 25 ohms.
The easiest way for you to measure the resistance of a ground rod is to use a clamp on ground tester.
This is an older type of resistance meter that uses multiple ground probes and wires to assess a ground rod s resistance.
The clamp on ground tester induces the ground rod with an ac signal that is then picked up by a receiving coil within the same clamp and uses the difference to calculate the resistance.
This is a different tool from the clamp on multimeter which only reads ac current.
Resistance should be less than 25 ohms if the system is connected properly.
If it is higher then you must place a second ground rod.
Nearly all electricians and electrical inspectors are familiar with the national electrical code requirement in sec.
250 54 which requires the resistance to ground of a single made electrode e g ground rod to be 25 ohms or less.
With this method the resistance of two electrodes in a series is measured by connecting the p1 and c1 terminals to the ground electrode under test.
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Reads ground resistance down to 0 10 ω.
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Touch one lead to your test wire and the other lead to your test location for example an outlet s third ground plug which is the small round hole at the bottom of the outlet.
There is no requirement to retest the resistance.
P2 and c2 connect to a separate all metallic grounding point like a water pipe or building steel.
The remaining ground electrodes are all in parallel and as a group are in series with the ground electrode being measured.
