Reversed polarity testers

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Greg1707

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Alexandria, VA
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Business owner Electrical contractor
Are those small inexpensive receptacle testers (the type that every home inspector owns) accurate in determining reversed polarity where there is no equipment ground present?
 
Are those small inexpensive receptacle testers (the type that every home inspector owns) accurate in determining reversed polarity where there is no equipment ground present?

No, not in my experience. Most of the time a reversed polarity light is really a no equipment ground light. Always had to open it up to see it though.
 
091212-1409 EST

The answer should be no.

However, if you make a patch cord that has no connection to the EGC pin in the plug and bring out an EGC on the socket end of the cord so that the EGC pin to the tester can be connected to a ground point somewhere, then you can make it work for testing the reversal of neutral and hot.

However, I can use my Fluke 27 to test if hot is connected to the correct terminal where there is no EGC as follows:

Fluke in AC volts. One meter lead goes into the wall socket. The other lead is in free space or I touch the probe tip.

In my basement hot to lead in free space reads about 18 V. When I touch the free space probe about 60 V. Difference is because of the difference in capacitance to earth. The neutral side is about 0.8 to free space, and to me about 1.5 V. The EGC to free space is about 0.3 V, and to me about 0.8 V.

In my living room, wood floor,
hot 18 and 37 V,
neutral 0.2 and 1.5,
EGC 0.8 and 3.5.

If the measurement is made to a good EGC that goes directly to the main panel, then:
neutral to a good separate EGC is 0.25 V,
and EGC at living room outlet to good separate EGC is 0.1 V.

It should be noted that I have an oscillation on these small signals resulting from the carrier signal from my TED energy monitoring system. i also have numerous other noise sources producing signals on the EGC lines.

The living room voltage being higher on the EGC is a little surprising, but my EGCs are about #15 wire vs #12 for neutral. That was standard in the early 60s. I do not have a real good explanation, and I do not plan to look for one currently.

However, this technique should be adequate to test for the hot lead, but it is better to use a reference wire to a known good ground reference.

Functionally this does about the same thing as a pencil type voltage tester that works on capacitive coupling.

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Are those small inexpensive receptacle testers (the type that every home inspector owns) accurate in determining reversed polarity where there is no equipment ground present?

I can't think of how it could with no reference to ground, but one of those non-contact AC testers that light up and beep will tell you which one is hot.

Exactly how do those things work anyhow? Capacitance? :confused:.

Considering that the non contact ones work, it seems it would be entirely possible to make a recepticle tester that showed polarity with no ground present. That would probably make the inexpensive part less inexpensive, though
 
Last edited:
091212-2054 EST

I received a very important PM about my previous post.

Do NOT touch the other meter probe when using any meter that does not have a very high impedance or by chance is in a current mode or low impedance mode. The Fluke 27 has a 10 megohm input impedance shunted by a small capacitor.

Also do not touch the free space probe tip if the source voltage is greater than nominal 120 V.

Thus, it would be best to just use the free air state of the probe or touch it to some metallic item that you are not touching.

Absolutely do not touch the test lead probe of any low impedance meter. This means a Simpson 260, solenoid meter, or a high impedance meter in a low impedance position.

Also note that the lower the input impedance of the meter the smaller would be any reading, and higher current thru you.

The approximate current at 120 V and 10 megohms is about 12 microamps.

.
 
091212-2054 EST


Do NOT touch the other meter probe when using any meter that does not have a very high impedance or by chance is in a current mode or low impedance mode.

Absolutely do not touch the test lead probe of any low impedance meter. This means a Simpson 260, solenoid meter, or a high impedance meter in a low impedance position.

Good advice! Don't be part of the circuit you are testing: you may become the fusible link!

I would add to the list of meter probes not to touch: megohm meters!
 
091212-2153 EST

jeremy:

That is also a very good point.

What all these comments mean is that anyone using an instrument should understand the operation of the instrument, its limitation, why, and the technical details of how it works.

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091212-2153 EST

jeremy:

That is also a very good point.

What all these comments mean is that anyone using an instrument should understand the operation of the instrument, its limitation, why, and the technical details of how it works.

.

Too bad we can't get the peddlers of all those residential power-saver devices to understand that. :cool:
 
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