Line fault at the outlet -- do I need an electrician?

I touched the red probe to the center and the black probe to the sides of the can and got 117 volts. That seems like the polarity is correct.

Assuming that the "can" you refer to is the socket into which a light bulb is inserted you were measuring between hot and neutral, rather than between safety ground and each of the other two wires (hot and neutral) as you were doing on the outlets. And if so, the measurement says nothing about polarity. Since this is AC you would have obtained the same reading if you reversed the connections of the red and black probes.

I’m surprised, though, that the reading was only 117 volts, and I'm not sure what to make of that. At the miswired outlets you variously measured 3.4 to 4 volts between ground and the miswired neutral, and 120 volts between ground and the miswired hot. And you measured 124 volts between ground and hot on other outlets in the same basement that are properly wired. As Jim pointed out earlier 120 + 4 = 124 volts, which seems unlikely to be a coincidence.

On the miswired outlets what do you measure between hot and neutral? As far as I can recall that has not yet been measured.

Best,
-- Al

I'm somewhat perplexed by the latest measurements, and I can't readily envision a miswire (or even multiple miswires, perhaps at the panel as well as at one or more of the outlets) that could account for these findings.  But what I would say at this point, given the possibility of multiple unknown miswires, is DO NOT ASSUME THAT TURNING OFF THE BREAKER WILL KILL THE ELECTRICITY TO THE OUTLET.  

Best,
-- Al

I gave your theory some thought and I can see where there would be an increase of current on the equipment grounding conductor as more leakage was present but I cannot see where the voltage would increase. If anything the voltage would decrease. Wouldn’t more leakage translate into a lower neutral to equipment ground resistance? The lower the resistance, the higher the current, the lower the voltage. Extreme example. 0 ohm resistance between the neutral and equipment grounding conductor.

Hi Jim,

With hot and neutral reversed and a component turned off 120 volts will be applied to the end of the primary winding of the power transformer in the component which normally receives AC neutral. AC neutral presumably goes nowhere in the component in that situation (other than perhaps to a line filter capacitor), assuming the component doesn’t have a standby mode or is not in standby mode, because its power switch is turned off. The 120 volts will leak to some degree to the chassis/AC safety ground of the component via stray capacitance in the transformer. That degree being different and I would imagine probably greater (perhaps much greater) than under normal circumstances when 120 volts is applied to the other end of the transformer via the power switch. So what I’m envisioning is that the reversal of hot and neutral will result in a significant voltage being applied to the safety ground, resulting in significant current through the safety ground wiring while no current exists in the neutral wiring, resulting in a significant voltage developing between safety ground and neutral as a result of that leakage.

I could be wrong about that, and admittedly creation of a 4 volt difference would seem to require a great deal of current. But nevertheless it seems to me to be a possible explanation. And as I said, if that is the main contributor to the 4 volts the issue will go away when hot and neutral are connected properly, without the need for further corrective action involving the wiring and connections.

Best regards,
-- Al

Hilde45, when you measured the 4 volts while the system was plugged in, were the components in the system turned on, or were they turned off or at least in standby? And as far as you know was anything else that is on the same branch turned on at the time?

If a lot of stuff was turned on at the time it increases the likelihood that the explanations cited by Erik and Jim apply. If not, it increases the likelihood that my hypothesis applies, namely that applying 120 volts to the AC neutral input of the component(s) resulted in excessive AC leakage to ground, mainly via their power transformers. Or, as heaudio123 alluded to, if significant current was being drawn by the components or other things the cause could have been a combination of both factors.

If my hypothesis was the main contributor, though, that issue should go away once the hot and neutral connections are reversed to what they should be.

Best regards,
-- Al

@Hilde45, when you measured the 4 volt difference between safety ground and the miswired "hot" terminal on the outlets was some or all of the equipment plugged in at the time? If so, I think it would be worthwhile to repeat that measurement with the equipment unplugged. In addition to the possible causes Erik has cited for the 4 volt measurement I’m thinking that applying 120 volts to the neutral of whatever equipment was plugged in could have resulted in AC leakage to ground within the component(s) that might have been responsible.

Jim ( @jea48 ), does that sound plausible to you?

Good luck. Best regards,
-- Al