The term “digital multimeter” gives you the impression that all you have to deal with are numbers.
It is easier to use than the analog counterpart and comes with little trouble.
However, you come across “OL” for the first time and get confused. “OL” is definitely not a number, and now you’re wondering what it actually means when you run tests on an electrical component.
This is exactly why we are here, as we tell you all you need to know about OL when it is displayed on your multimeter screen.
Let’s get right to it.
What Does OL Mean On A Multimeter
OL is an abbreviation for “Open Loop” on the multimeter screen and represents different things for different tests and multimeter modes. It means there’s no continuity between the positive and negative multimeter probe or the voltage in a circuit exceeds the test limit.
There’s a whole lot more to know about what OL readings mean and we will get into these.
From the basics, current runs through a path within a circuit. This is a conductive metal through which current runs from one end to another.
Assume a circuit to be a plumbing system where the current is water and the pipe is the conductive path or metal that carries water from one end to another.
This is the best analogy that’ll make you understand what OL or Open Loop means on the multimeter screen when you run different tests.
What OL Means When Testing Continuity
A continuity test is a test on the uninterrupted flow of electricity on a conductive path. If there is an interruption between two points in a circuit, then there is no continuity.
Now, when there is no continuity, the meter screen displays OL, showing that there’s an opening within the loop (hence, open loop).
For instance, when you use a multimeter to test a wire for faults, OL means there’s a problem with the conductive copper between the points where you place the negative and positive multimeter probes.
Using our analogy, when a water pipe is broken and water does not flow from one end of the pipe to the other end of the pipe, there’s an interruption of the path between these two points.
This means there’s no continuity and, when testing a circuit, the meter screen presents an Open Loop reading.
Although this is usually caused by a short circuit, OL will be displayed any time the multimeter probes don’t connect within the circuit.
This means bad multimeter lead placements or dirt on the tip of your leads will cause the meter screen to display OL.
What OL Means When Testing Voltage
Voltage is the electrical potential or pressure of current between two points within a circuit.
When measuring volt with the use of a multimeter, there are different ranges you may set the dial to, depending on the amount of volt you wish to test.
You also set the dial to the closest but higher volt range.
For instance, when measuring a low volt like 1V within a circuit, you set the multimeter dial to the 2-volt range. When measuring high volt, like 400V, you set the dial to the 600V range for accuracy.
If the meter screen displays “OL”, then there is more volt than the range the multimeter is set to test (overload). This is the same when testing high and low currents, and the meter may also display “1” in some cases.
For the 2V range, for example, if the volt you measure within the circuit is more than 2 volts, the meter will display OL or 1, signifying an overload.
The solution to this is to adjust the multimeter dial to a higher range.
What OL Means When Testing Resistance
Resistance is the opposition to the free flow of current within a circuit. The higher the resistance, the harder it is for current to flow from one point to another. Zero (0) is the lowest resistance you may get within a circuit.
Now, when you measure resistance, you turn the multimeter dial to the “Ohms” setting represented by “Ω”.
If the multimeter displays an OL reading, then there is infinite resistance between the two points you are testing. An infinite resistance reading is an important topic to be discussed on its own.
What Is Infinite Resistance
To explain this term, we will pick certain parts from our definition of resistance.
“The lower the resistance, the easier it is for current to flow, and the higher the resistance, the harder it is for current to flow”.
An infinite resistance is extremely high, which means what you are testing cannot allow electricity to go through.
In this case, there is no connection between the two multimeter probes and the multimeter then thinks the conductive pathway has been interrupted. You then get “OL” on the multimeter’s screen.
We may use our plumbing system analogy. Water going from one end of a pipe to the other has low resistance.
When the pipe is half-blocked, it has high resistance, but water still goes through to the other end. This is why the meter still presents a reading.
Now, when the pipe is almost completely blocked or totally blocked, it has infinite resistance and water does not go through to the other end at all. In a circuit, the meter reads this as OL.
As you may have guessed, the resistance test is another accurate method of testing for continuity within a circuit. It is usually used when your multimeter does not have a continuity mode.
Clarifying On Zero (0) Ohms And OL Resistance Readings
Some confusion may arise on the difference between OL and “0” Ohms when measuring Ohm or resistance.
This is mainly because “0” usually represents the absence of something important. With resistance, this isn’t the case.
As we have said, in the Ohms setting, zero is the lowest and best resistance you may measure within a conductor.
OL is the extreme opposite of it, as it means there’s complete resistance to the flow of electricity, preventing it from moving from one point to another.
When measuring resistance and you come across any of these, this is the only difference you need to know between the two.
The OL reading on the multimeter represents a plethora of things depending on what you are testing or the mode your multimeter is set to.
It means there’s no continuity in the continuity mode, excess volt or overload in the voltage measurement setting, and infinite resistance in the Ohms setting.
Learn more about the multimeter and the different diagnoses you may run with this useful tool. You will need it for a lot of tests.
Frequently Asked Questions
Is OL A Good Reading On Multimeter?
OL (open loop) is never a good reading on the multimeter, as it represents different kinds of faults within an electrical circuit. It either represents zero continuity, infinite resistance, or excess voltage.
What Does It Mean When A Capacitor Reads OL?
When testing a capacitor, OL (open loop) either indicates that there’s no continuity within its circuit, or the capacitance or voltage is more than the range the multimeter is set to.
Alex Klein is an electrical engineer with more than 15 years of expertise. He is the host of the Electro University YouTube channel, which has thousands of subscribers.