Basic Electrical Troubleshooting or “How To Use Meters” (part 3)


We now understand that an electrical circuit is made up of power sources, switches, and light bulbs but in order to use meters to diagnose an electrical circuit, we need to understand what the electricity is doing. We need to understand what to look for in the circuit.  We need to know how to diagnose light bulbs. The following is a primer on electricity.

I think we need to first understand what is voltage, amps and ohms.  This is what we will be measuring with our meters.  It is easiest explained if you think of electricity in terms of water (see picture below). Then look at the generator picture and you can see the relationship.  The “pressure gauge on the tank would be the same as your reading on a volt meter. The water in the tank is the electrons or amperage. The wires are the pipe size and the faucet is the switch. And the bottom picture explains resistance.

What is voltage? in the picture is a huge water tank filled with thousands of gallons of water — maybe a water tower. The difference between the pressure of water in the tank and the water that comes out of a pipe connected at the bottom leading to a faucet is determined by the size of the pipe and the size of the outlet of the faucet. This difference of pressure between the two can be thought of as potential voltage.  Voltage is the difference in electric potential between 2 points. Voltage is measured in VOLTS, the size of the water tank. Voltage drop is the amount of voltage lost through any type of switching device or conductor (the pipe of the faucet).

What is current? it is the amount of flow (gallons per minute) determined by the pressure (voltage) of the water thru the pipes leading to a faucet. The term current refers to the quantity, volume or intensity of electrical flow, as opposed to voltage, which refers to the force or “pressure” causing the current flow. Current is measured in amperes (related to the pressure (Voltage) of water thru the pipes and faucet). Or think of it in terms of a river flowing.  The water is the voltage and the current is the intensity of the flow.  When the current in the river increases, more water flows at that point. 

What is resistance? Resistance would be the size of the water pipes and the size of the faucet. The larger the pipe and the faucet (less resistance), the more water that comes out! The smaller the pipe and faucet, (more resistance), the less water that comes out! Resistance is measured in ohms.

Now, with this understanding of electricity, we can better understand what we are trying to read with our meters?

In Part 4 of this post, we will finally see how to use the meters we have.  Hopefully, up to now, these 3 posts have helped you better understand electricity and with this knowledge, will have you reading electrical circuits and diagnosing problems accurately when they occur.

Don’t miss part 4 — coming to you soon!!!!

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About yorkcentraltechtalk

I have been in the HVAC industry most of my life. I worked 25 years for contractors on anything from residential to large commercial boilers and power burners. For the past 23+ years I had been employed by York International UPG Division ( a division of Johnson Controls) as a Technical support/Service Manager but I am now retired. One of my goals has always been to "educate" dealers and contractors. The reason for starting this blog was to share some knowledge, thoughts, ideas, etc with anyone who takes the time to read it. The contents of this blog are my own opinions, thoughts, experiences and should not be construed as those of Johnson Controls York UPG in any way. I hope you find this a help. I always welcome comments and suggestions for postings and will do my best to address any thoughts, questions, or topics you may want to hear about. Thanks for taking the time to read my postings! Mike Bishop
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One Response to Basic Electrical Troubleshooting or “How To Use Meters” (part 3)

  1. trachsel says:

    I always use the water behind the dam analogy. Good stuff!

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