How To Test Amperage / Amp Draw and properly measure and fuse a circuit



How to Measure Amperage

Amperage is the amount of electrical current running through an electrical component, such as a wire. Specifically, amperage measures the number of electrons passing a given point in a given period of time, with 1 ampere (or "amp") equal to 1 coulomb per second. Measuring amperage is an important task when working with electrical systems, primarily to make sure that wires are not handling more current than they are rated for. You can measure amperage with a special tool called a multimeter.

Steps

  1. Always test your meter first!Set the function to ohms. It should read approximately zero when the test leads are touched together. It should read 1 when separated. If not, check your batteries.
  2. Determine the amperage rating for your digital multimeter.A multimeter is a small hand held device that is most commonly used to measure voltage, resistance, and amperage, but more advanced units can also measure capacitance, frequency, and temperature. Each model will only be rated to handle a certain amount of current, and this rating needs to be adequate for the electrical system you want to test. For example, running 200 amps through a multimeter rated for 10 amps will ruin the multimeter's fuse. The amperage rating will be printed on the unit or in the owner's manual.
  3. Select the appropriate function on your multimeter.Most multimeters have functions for measuring several different quantities. To measure amperage, you need to set the function to either measure AC amperage or DC amperage, depending on the electrical system you are testing. The power source for your system will determine the type of current. For example, household power is AC, while power from a battery is DC.
  4. Set the range on your multimeter.To ensure that you don't blow your device's fuse, set the maximum amperage sensitivity to well above your expected reading. You can adjust this downward if the multimeter does not read anything when hooked into your system.
  5. Plug the leads into the appropriate terminals.Your multimeter should come with 2 cords, each with a probe on 1 end and a lead on the other. Plug both cords into the correct terminals for measuring amperage; the owner's manual will specify the correct terminals if they are not labeled clearly.
  6. Run the circuit through the multimeter to measure the current.Warning: Working with electrical wires is extremely dangerous and can cause electrical shock, even low voltage sources. Turn off all breakers before working with household wiring and use an AC current sense probe to see if AC is absolutely off before touching any wires, especially bare ones. Do not work in a wet environment on even a high humidity one. This can conduct electricity and hurt you. Wear heavy rubber gloves. Additional precautions may be necessary. Consult a real electrical workbook (not an online source) before attempting this. Assume wires can have missing insulation from accidental damage during installation or old age. Missing insulation can cause electrical shock. Always have someone with a cell phone, who is not touching you or the wiring, ready to call an Emergency number in case of emergency. This person should also be trained in first aid and CPR. If electrical shock occurs, this person may have to remove you using some type of insulated material (a dry and thick cloth for example but something else may need to be used) or else that person will also undergo shock due to the conductivity of skin and maybe some clothing (and other materials). Always consult a real electrical safety book before attempting this and know what type of signal you are dealing with.Clip the wire in a single spot and strip back the insulation on both exposed ends. Secure these ends separately to the leads of the amp meter. Only do the measurement after the wires are securely attached to the amperage meter probes. Make sure these wires especially the exposed ends cannot touch you. Turn back on the breaker and adjust the meter sensitivity if no reading is produced.
  7. Turn off the breaker and use an AC current sense probe to make sure AC is off; Then and only then, rewire the circuit.Follow the precautions outlined in step 5 and consult a real electrical book (not an online source) for safety precautions. After taking your reading, you will need to complete the broken circuit again. It is much safer to do this by buying and installing new wire rather than trying to patch the area where you cut it.

Community Q&A

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  • Question
    How many amps is 9 volts?
    wikiHow Contributor
    Community Answer
    Amperage = Volts/Resistance, so you need to input the resistance of the material.
    Thanks!
  • Question
    Can I measure DC amps by removing the fuse in a 12-volt light circuit and using my multi-meter in place of the fuse?
    wikiHow Contributor
    Community Answer
    You can if your multi-meter has amps DC. Look for a solid line over a dashed line over an A, like Ǟ. Turn your dial to that, put your black probe into your meter's COM port and the red probe into your meter's fused port that is rated higher than the fuse you are pulling or the rated amperage of the circuit. Then all you have to do is complete the circuit with your meter. The most important part is the fused port. If the fuse in your circuit is 12A, for example, and your meter has 2 fused ports for 10A and 300mA, you are out of luck, you might ruin your meter.
    Thanks!
  • Question
    What is a good reading for a 220 breaker on an amp tester?
    wikiHow Contributor
    Community Answer
    See what the amp rating is on the breaker. Once you have determined the rating you want to make sure you do not exceed 80% of that rating. For example, if it is a 20 amp breaker you do not want the amp draw to exceed 16 amps, 30 amp breaker should not exceed 24 amps. This applies to any circuit breaker.
    Thanks!
  • Question
    How can I work out a parallel DC circuit's amperage without using a machine to measure it?
    wikiHow Contributor
    Community Answer
    The same way, but you might need to switch from AC to DC. Read the manual to get the exact answer.
    Thanks!
  • Question
    How can I check the amp for a cooker circuit?
    wikiHow Contributor
    Community Answer
    Use a multi-meter and set it for amps. Test the red LED coming in.
    Thanks!
  • Question
    How do you read 220 volts?
    wikiHow Contributor
    Community Answer
    Put one lead to one hot wire, and the other lead to the second hot wire. It should read 240 volts. If you put one lead to ground and other to a hot wire, it should read 120 volts. One hot wire = 120 volts + one hit hire = 240 volts.
    Thanks!
  • Question
    How do I measure 10 amps dc in multimeter?
    wikiHow Contributor
    Community Answer
    Set the multimeter to A with the weird line next to it and select the 10 setting.
    Thanks!
  • Question
    How do I get a 30 amp system off a 100 amp breaker box?
    wikiHow Contributor
    Community Answer
    Assuming it's a 220v system/circuit, you'll need #10 (10/2) wire tied to a two pole 30 amp breaker, and hopefully you have two free spaces in the panel for the breaker.
    Thanks!
  • Question
    Should I use the positive or the negative wire to check the amps?
    wikiHow Contributor
    Community Answer
    On a standard digital multimeter (DMM), there are usually 3 or 4 terminals, depending on the type and the brand. On a simple multimeter, you'll see Com, Positive, and 10A. Com is common (and connects to the black probe), and it's always connected to either Positive (red) or 10A. However, you need to be careful; what you call "checking amps" requires more knowledge than that!
    Thanks!
  • Question
    How can I check the amps in my appliance?
    wikiHow Contributor
    Community Answer
    Use an amp checker, which you can get big retail stores. Put the negative to the negative, and the positive to the positive.
    Thanks!
Unanswered Questions
  • When buying an electrical appliance (a tiller), which comes in 9 amp and 12 amp, is bigger better?
  • Please help , I am relocating may manufacturing business to a new location need 300 amps , how to check?
  • What scales are used for finding current on an analog meter?
  • How can I measure the amps in a 12volt and 150ah battery?
  • How do I test the amperage on a welding machine using a clamp style meter?
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Video

Quick Summary

Before you attempt to measure amperage, turn off all of the breakers and use an AC current sense probe to make sure the power is absolutely off. When you’re ready to take the reading, select AC or DC amperage on the meter, depending on the electrical system you are testing, and make sure the multimeter is set to the range of the amperage you’re testing. Plug the leads into the appropriate terminals, then clip the wire and strip back the insulation on both ends. Secure these ends separately to the leads of the meter, then turn on the meter to take the reading.

Did this summary help you?
  • Wear heavy rubber gloves when working with live circuits.
  • Always read the owner's manual entirely to address safety concerns before working with the multimeter.

Warnings

  • Always read a real electrical book (not an online source) before working with any voltage or current source (especially high ones)
  • Do not work in a wet environment on even a high humidity one. This can conduct electricity and hurt you.
  • Electricity can cause electrical shock and even death
  • Have an extra person with a cell phone for emergency. Check the cell phone for charge and bars before working. The person should also be trained in First AID and CPR. Do not let this person touch you while you are working on the circuit.
  • Be cautious of bare skin and even clothing and other materials can conduct
  • Wear heavy rubber gloves when working with live circuits.
  • Always read the owner's manual entirely to address safety concerns before working with the multimeter.

Things You'll Need

  • Digital multimeter
  • Wire cutters
  • Rubber gloves

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Date: 19.12.2018, 12:44 / Views: 91494