In practice for a residential structure most electricians place two ground rods and call it done.
Ground rod resistance tester.
The remaining ground electrodes are all in parallel and as a group are in series with the ground electrode being measured.
You are correct that the nec states that if you use one ground rod that the resistance to ground must be 25 ohms.
If it is higher then you must place a second ground rod.
Molded carrying case 9v alkaline battery and calibration verification loop.
Measure grounding circuit performance without disrupting service.
This is a different tool from the clamp on multimeter which only reads ac current.
Unfortunately it seems many electrical professionals.
Fully auto ranging with data hold to capture readings.
Nearly all electricians and electrical inspectors are familiar with the national electrical code requirement in sec.
The easiest way for you to measure the resistance of a ground rod is to use a clamp on ground tester.
Reads ground resistance down to 0 10 ω.
250 54 which requires the resistance to ground of a single made electrode e g ground rod to be 25 ohms or less.
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.
Using an earth electrode tester instead of a clamp on tester will take a lot more time and effort.
This type of tester is usually available at hardware and home improvement stores as well as from online retailers.
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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.
Resistance should be less than 25 ohms if the system is connected properly.
This is an older type of resistance meter that uses multiple ground probes and wires to assess a ground rod s resistance.
There is no requirement to retest the resistance.
Aemc 6471 multi function ground resistance tester kit 500 ohms resistance 32v voltage 250 ma current by aemc 2 802 50 2 802.
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.
In areas where driving ground rods may be impractical the two point method can be used.
