Hopefully you have all been practicing with your new multimeters and nobody has gotten hurt doing it. In our last post about using your meter I suggested checking the voltage at a normal residential outlet. With your meter on AC volts you should measure somewhere around 115 to 120 volts AC. This is what you would EXPECT to read. If you get it, that is normal and if you get something very different from that, you are getting an incorrect reading. The important point here is that when you set out to make some kind of electrical measurement, you should have some idea of what to expect. This way you will know if something is wrong. Having an idea what to expect is a very important concept when troubleshooting electrical systems.
Now, let’s think back to when you checked that 120 volt AC outlet. You set your meter to read AC volts and you inserted your meter leads into the to slots on the outlet and read somewhere around 120 volts AC. Notice that one of the slots is slightly larger than the other. Typically this is the slot on the left. That slot should be the NEUTRAL connection and the other slot would be the HOT connection. Keep in mind that both of these terms are relative, meaning that the hot connection is only hot with respect to ground, while neutral is not hot with respect to ground, it is neutral.
If you want to prove this, get out your meter, insert one lead into the neutral slot and the other meter lead into the ground “hole” on the outlet. If you outlet is wired properly, you should expect to read 0 volts. Next, insert one lead into the hot slot and the other lead into the ground hole. You should now read 120 volts AC. This is normal, and expected and what we have seen is that there is 120 volts “pressure” between hot and neutral, between hot and ground, and there is 0 volts pressure between neutral and ground. This means neutral and ground are the same voltage.
Noodle on these concepts for a while and we will talk more about them later, keeping in mind that voltage is pressure and that pressure is relative to some other point. In some ways it is similar to asking the question, “how far are you from home?” Of course the answer depends on where you are and the distance from home is related to where you are. Like I said, think it over. It really makes sense. Really!!