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If you have a suspicion regarding your homes electrical supply or aim to start troubleshooting a problem checking voltage at the nearest receptacle to the problem load should be your first step. These three main initial readings you should take at a receptacle using a multi-meter will put you on the right path to a pain free troubleshooting experience. The readings will be the hot-neutral voltage, neutral-ground voltage and hot-ground yovoltage.
Mis-wired receptacles are not uncommon, a three slot receptacle has a hot slot, neutral slot and ground slot. The short slot is hot, the long slot is neutral and the u-shaped slot is ground. Now, are the hot and neutral swapped? Is the ground and neutral swapped or shorted? these conditions can actually go undetected for a long time because loads are generally indifferent to polarity because they are just converting AC to DC in their internal power supplies like our phone chargers. However, there are sensitive electronics like computers and instrumentation where polarity does matter.
Hot-Neutral Voltage - This is the load voltage, essentially what the device is drawing to work. lets assume we have a reading of 118V.
Neutral-Ground Voltage - Under load you would have a small reading, lets assume 2V that indicates current flowing through the impedence of the white wire.
Hot-Ground Voltage - this is your source voltage from the panel and you should read 120V.
How to Spot irregular Conditions:
Measuring between hot-neutral will not tell you if your hot and neutral are swapped but if your neutral ground voltage is 120V and hot-ground is a few volts less then hot and neutral then the two have been reversed and needs to be fixed.
Under load conditions there should be some neutral-ground voltage generally 2V or less.
Checking to see if neutral and ground have been switched measure hot-neutral and hot-ground under load. Hot ground should be higher then neutral ground if not then this is actually a safety concern and only once power is removed is it acceptable to fix or call a certified electrician.
Handy Receptacle Checker:
Every one should own one of these either at home or in their tool bags. The Klein Receptacle Tester.