So if he has a 3V differential between ac neutral and ac safety ground at the particular outlet he measured, let's make the following rough assumptions:
-- 100 feet of wiring from the outlet to where those two lines are bonded together at the service panel.
-- Negligible current flowing through the safety ground wiring.
-- Wire resistance of 1.6 ohms per thousand feet (corresponding approximately to 12 gauge wire). Which would mean 0.16 ohms for 100 feet.
That would mean, if the resistance through the path is what it should be, that he has 3/0.16 = 18.75 amps flowing through the neutral wiring on that line.
Sounds kind of high, suggesting that perhaps the resistance is higher than it should be somewhere in the neutral run.
Al,
Voltage drop, (VD), would come into play I would think for the 3 volt difference of potential between the neutral and the equipment grounding conductor. And for VD to exist we need a connected load across the hot and neutral conductors of the branch circuit. The greater the load the more VD. ( NEC
recommends that the VD drop for a combination feeder / branch circuit should not exceed 5%)
The 3 volts Nick measured from the neut to the grd could of been the result of connected loads on the branch circuit and VD.
We do not have the whole picture though just what wiring method was used for Rick's Condo. I can only assume each condo has its own electric meter. Are the meters all located together in a common meter bank? Is the main disconnect, (breaker), for each condo electrical service outside by its respective meter? If the main disconnect is outside by the meter then I assume the service neutral was connected to earth there. I assume the electrical panel is inside the condo unit. If that is the case then 4 conductors were ran from the disconnect to the electrical panel. 2 hots, 1 neut, and 1 equipment grounding conductor.
At the electrical panel a separated isolated neutral bar is needed and a separate equipment ground bar. What is the distance the main disconnect is from the electrical panel?
So without knowing how rick's condo is wired it hard to give a good answer regarding the 3 volts.
I believe though, from memory, NEC says at the end of a branch circuit there shall not be more than 1 ohm of resistance between the neutral and equipment grounding conductor. To check naturally the branch circuit would need to be de energized and any loads disconnected from the branch circuit.
3 volts....... It could just be his meter registering phantom voltage. High resistance digital volt meters are notorious for giving erroneous readings at times when not connected across a load. Jmho you can't beat a good old analog meter.
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If I take a reading on that plug the voltage drop is from 123.8 to 110. (measured across both vertical slots). However, if I measure from the short vertical to the ground then it reads 116v. If I turn off the kettle the reading goes back to the 123.8.
09-12-09: Nick_sr
VD is definitely more than 5%....
I would check around for a good electrical contractor. Preferably a commercial/industrial electrical contractor. The contractor will send out a service driver electrician with trouble shooting experience and find and fix the problem. One hour of labor probably around $100 - $150 bucks.... If the problem is by chance on the Line side of the electric meter the electrician will call the utility company's service department.
Jim
