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Posted: 9/19/2023 8:25:32 AM EST
[Last Edit: flcracker]
Is my new multimeter broken, or am I doing this wrong?
I just bought this Ideal 61-737 multimeter at Lowes. The reason I bought it was to measure the current being delivered at the end of a 100-ft 12/3 extension cord that is plugged in to a "supposedly" 30-amp outlet in a storage container workshop. The extension cord is run to another storage container workshop where I have plugged in a refrigerator. I'd like to know if the current is sufficient to not burn up the motor in the fridge. The instructions seem pretty straightforward:  Attached FileHowever, when I put the clamp around the extension cord the meter reads 00.00 A. Same with any other power cord plugged in to any working device. Is it my brain or the meter that isn't working properly? What is the proper way to do this? |
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Posted: 9/19/2023 8:31:39 AM EST
[#1]
Only measure one wire at a time, that means might have to split the jacket to get at just one wire, not the ground. Use some cheaper cord you don't care too much about
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Posted: 9/19/2023 8:36:08 AM EST
[Last Edit: Hawken50]
[#2]
the thing in the 3rd illustration is a splitter. you can only measure amps on one wire at a time. the splitter separates the hot and neutral so you can get a reading.
Plug your cord into the splitter, plug the splitter into the wall. your alternative is to find unsheathed wire in the outlet box itself or in your breaker box. ETA: to be clear, when I say "unsheathed" wire, I'm referring to the outer jacketing that holds the hot and neutral together, NOT the wire insulation itself. You can read amps on an insulated wire, but not on 2 wires. |
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Posted: 9/19/2023 8:46:36 AM EST
[#3]
You need a line splitter to measure a single line of the extension cord. The AC power in the cord cancels itself out when measuring the entire cord at once.
 Also, you'll probably be better served measuring the voltage drop at the end of the cord. The cord will supply 30 amps for a limited duration, but the distance will create a resistance. As the voltage drops due to the resistance, the amps increase to sustain the actual power requirement of the equipment. At some point this will damage the equipment, the cord, or trip the breaker but can be measured or calculated before hand. |
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Posted: 9/19/2023 8:55:35 AM EST
[#4]
IMHO...
You need to find one of those charts that predict the drop over the total distance of the run by the Gauge of wire ran. The Amp meter is not going to do it. I mean if your fridge says it has a 120v, 6 amp Max draw, but you check it when its running idle, it might only be drawing 3 amps. The fact that it tells you its only pulling 3 amps means it only pulling 3 amps, its doesn't mean it can pull 6+ though your total run... Hopefully, I'm making sense. I often get crap in my head and can't elaborate on my train of thought clearly to folks. |
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Posted: 9/19/2023 9:07:39 AM EST
[#5]
You're doing what's in the middle of the picture. The circle with the slash on it means "don't do this, it isn't going to work." Just measure the current on one wire.
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Posted: 9/19/2023 9:15:28 AM EST
[#6]
Thank you - all of this is very helpful.
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PA, USA
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Posted: 9/19/2023 11:03:01 AM EST
[#7]
What everyone else said.
Here is the reasoning: as the name suggests, "Alternating Current" constantly alternates the direction of the current flow (60 times a second for household wiring, hence 60hz). So in a given moment of time, the current is running one direction on your hot wire, and the opposite direction on your neutral wire. 1/60th of a second later, it reverses. So, when you are trying to measure current at these two points at the same time, they cancel each other out. |
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MO, USA
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Posted: 9/19/2023 1:29:07 PM EST
[#8]
I have an app on my phone from south wire called voltage drop
Download it. It’s very useful. What’s the rates amperage draw for the fridge? Is it 120v? Assuming 120v that 100ft 12 gauge wire is only good for 9 amps at a 3 percent voltage drop max. |
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Posted: 9/19/2023 2:04:58 PM EST
[#9]
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USA
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Posted: 9/19/2023 10:28:56 PM EST
[Last Edit: Meet_Poll]
[#10]
Quote HistoryOriginally Posted By Quicky06: I have an app on my phone from south wire called voltage drop Download it. It’s very useful. What’s the rates amperage draw for the fridge? Is it 120v? Assuming 120v that 100ft 12 gauge wire is only good for 9 amps at a 3 percent voltage drop max. This is a good answer, although the entire operation is unnecessary. OP could check voltage drop at the end of your cord but you’re already given 5 volts by the mgr. Amps tells you very little |
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Posted: 9/20/2023 8:42:58 PM EST
[Last Edit: pedaler]
[#11]
Quote HistoryOriginally Posted By blwngazkit: You need a line splitter to measure a single line of the extension cord. The AC power in the cord cancels itself out when measuring the entire cord at once. https://m.media-amazon.com/images/I/71JawOBQp6L._AC_SL1335_.jpg Also, you'll probably be better served measuring the voltage drop at the end of the cord. The cord will supply 30 amps for a limited duration, but the distance will create a resistance. As the voltage drops due to the resistance, the amps increase to sustain the actual power requirement of the equipment. At some point this will damage the equipment, the cord, or trip the breaker but can be measured or calculated before hand. Of all the stuff didn't know I need.....I swear this place separates me fron my money. |
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Posted: 9/21/2023 6:15:21 AM EST
[#12]
Originally Posted By flcracker: Is my new multimeter broken, or am I doing this wrong? I just bought this Ideal 61-737 multimeter at Lowes. The reason I bought it was to measure the current being delivered at the end of a 100-ft 12/3 extension cord that is plugged in to a "supposedly" 30-amp outlet in a storage container workshop. The extension cord is run to another storage container workshop where I have plugged in a refrigerator. I'd like to know if the current is sufficient to not burn up the motor in the fridge. The instructions seem pretty straightforward: https://www.ar15.com/media/mediaFiles/74872/1000006067_jpg-2959155.JPG However, when I put the clamp around the extension cord the meter reads 00.00 A. Same with any other power cord plugged in to any working device. Is it my brain or the meter that isn't working properly? What is the proper way to do this? I was gonna snap a picture of how to do it but the battery in my meter is dead. 
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Posted: 9/21/2023 8:58:27 AM EST
[#13]
Thank you - yes, it came with leads. I'll be back there tomorrow to do some rearranging in the container and will test the voltage as you described.
FYI - this fridge will soon become a temperature- & humidity-controlled meat curing chamber for salami & salumi. Looking forward to some sopressata, cacciatore, saucisson sec, and lonza. |
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OH, USA
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Posted: 9/21/2023 12:03:25 PM EST
[#14]
I would suggest a plug-in power meter to give you better feed back. It can measure power over time and record max draw and other things of interest, where the DMM will only tell you real time data.
Also, a note of concern, I don't know that this setup is wise on a 30A supply as it can be a potential fire hazard. A 12 gauge extension cord can melt before the breaker trips if something goes awry. Example meter - https://www.amazon.com/P3-P4400-Electricity-Usage-Monitor/dp/B00009MDBU |
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Posted: 9/21/2023 4:50:02 PM EST
[Last Edit: dangerdan]
[#15]
Depending on what all is on that circuit, but if nothing else, you'll have enough amps and just enough voltage.
Current is your limiting factor on load in a parallel circuit (such as majority of your wiring. Or common house wiring). Voltage stays pretty constant, but drops over distance due to resistance in the wire. |
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OR, USA
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Posted: 10/5/2023 10:39:58 PM EST
[#16]
Quote HistoryOriginally Posted By smullen: IMHO... You need to find one of those charts that predict the drop over the total distance of the run by the Gauge of wire ran. The Amp meter is not going to do it. I mean if your fridge says it has a 120v, 6 amp Max draw, but you check it when its running idle, it might only be drawing 3 amps. The fact that it tells you its only pulling 3 amps means it only pulling 3 amps, its doesn't mean it can pull 6+ though your total run... Hopefully, I'm making sense. I often get crap in my head and can't elaborate on my train of thought clearly to folks. Learned to measure the length of a wire using a Hioki milliohm meter last week, cool stuff. I'm in the automotive world, length of wire is generally insignificant in our systems. |
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Posted: 11/3/2023 7:08:09 PM EST
[#17]
Quote HistoryOriginally Posted By blwngazkit: You need a line splitter to measure a single line of the extension cord. The AC power in the cord cancels itself out when measuring the entire cord at once. https://m.media-amazon.com/images/I/71JawOBQp6L._AC_SL1335_.jpg Also, you'll probably be better served measuring the voltage drop at the end of the cord. The cord will supply 30 amps for a limited duration, but the distance will create a resistance. As the voltage drops due to the resistance, the amps increase to sustain the actual power requirement of the equipment. At some point this will damage the equipment, the cord, or trip the breaker but can be measured or calculated before hand. |
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