Would my circuit tester read neutral as being open if house neutral were disconnected, but grounding electrode to water pipe was connected?
My understanding is that grounding electrode conductors have around 25 ohms impedance, whereas house neutrals to transformers are about 2-5 ohms.
My electrical inspection teacher (for home inspection course) gave this as a bonus question on our final, but wasn't sure himself what the tester would read.
Thanks.
Peter Shepherd
If the utility used all metal piping you might not even know the neutral was open. Generally what you will see is an unbalance between phase to neutral readings, depending on the load imbalance. Your 3 light tester would look fine until that unbalance got so bad it wouldn't excite the neon. (
If your electrical system is properly bonded to the incoming water piping, and the piping has a continuous metallic path to your neighbor's house (and to powerline neutral through their breaker panel), then the water piping will act as a neutral return path.
A bit more voltage drop than usual, but it will work for a while.
Assuming the typical three-light plug-in circuit detector, it will indicate a normal circuit. It uses neon lamps that will light with several thousand ohms in the circuit, so the earth resistance will not affect it.
That is a common misunderstanding. The resistance of the earth path back to the transformer could be a lot more than 25 ohms. The 25 ohm figure is the code requirement for a single made electrode, and is only the electrode to earth resistance. The actual electrode to transformer resistance could in fact be several hundred ohms.
Ben Miller
Probably not. Don't depend on it for that purpose.
25 ohms is plenty to light up the neon lamps in those testers. In addition, with 120V loads connected to both sides of a 240V service, there will be a low enough impedance path to hold the neutral close to 0 volts. Close enough to fool your tester and give the appearance of a good neutral.I would have expected a little better understanding of the subject matter by an instructor.
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