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Author Topic: Measuring Current in Multi-conductor Wire  (Read 3355 times)

Jeff Lelko

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Measuring Current in Multi-conductor Wire
« on: January 28, 2016, 07:37:20 PM »

Hi All,

So I've been trying to figure out how to measure the current passing through a multi-conductor wire such as the basic 12/3 cable.  I have a plug-in meter that I've been using for years when bench testing gear to get baseline current consumptions, but is there a way to use a clamp-on meter or similar to get these readings when out on a job and I can't be unplugging things?  I've seen the wire splitters that allow for this, but I really don't want to patch one into every circuit I'm running just in case I'd like to see how much current I'm drawing.  Any thoughts?

Thanks!
-Jeff 
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Mike Sokol

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Re: Measuring Current in Multi-conductor Wire
« Reply #1 on: January 28, 2016, 08:09:23 PM »

So I've been trying to figure out how to measure the current passing through a multi-conductor wire such as the basic 1o use 2/3 cable. 

Without separating out the current return path, I don't know of any way to use a clamp ammeter to find current flow in a multi-conductor table. Of course, that's because same current flow in the two different directions cancel each other out. See a video I did on this at https://www.youtube.com/watch?v=z-KfZvbjyBY

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Jeff Lelko

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Re: Measuring Current in Multi-conductor Wire
« Reply #2 on: January 28, 2016, 09:38:01 PM »

Without separating out the current return path, I don't know of any way to use a clamp ammeter to find current flow in a multi-conductor table. Of course, that's because same current flow in the two different directions cancel each other out. See a video I did on this at https://www.youtube.com/watch?v=z-KfZvbjyBY

Mike Sokol

I actually watched your video earlier this evening!  Very informative and the reasoning makes perfect sense, so thanks for sharing.  I just know that peeling off some insulation to measure current would be frowned upon when on a job.  It's too bad that someone doesn't make a more elegant wire splitter versus the plastic blocks! 

-Jeff
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Frank DeWitt

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Re: Measuring Current in Multi-conductor Wire
« Reply #3 on: January 28, 2016, 10:35:20 PM »

  It's too bad that someone doesn't make a more elegant wire splitter versus the plastic blocks! 

-Jeff

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Stephen Swaffer

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Re: Measuring Current in Multi-conductor Wire
« Reply #4 on: January 28, 2016, 10:44:18 PM »

The plastic blocks may not be "elegant", but they do give you the option of a X10 multiplier for better accuracy.  I have considered rolling my own with SO/cord ends and shrink tubing to make it durable-but I am sure in a public place they would not be viewed favorably.  Besides, the blocks are pretty durable when thrown in a tool box-unlike a "wire" style solution.
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John Lackner

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Re: Measuring Current in Multi-conductor Wire
« Reply #5 on: February 05, 2016, 05:15:10 PM »

Hi All,

So I've been trying to figure out how to measure the current passing through a multi-conductor wire such as the basic 12/3 cable.  I have a plug-in meter that I've been using for years when bench testing gear to get baseline current consumptions, but is there a way to use a clamp-on meter or similar to get these readings when out on a job and I can't be unplugging things?  I've seen the wire splitters that allow for this, but I really don't want to patch one into every circuit I'm running just in case I'd like to see how much current I'm drawing.  Any thoughts?

Thanks!
-Jeff

Maybe you can try using a Kila-watt plugin and do the math.
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Jonathan Johnson

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Re: Measuring Current in Multi-conductor Wire
« Reply #6 on: February 05, 2016, 05:25:21 PM »

...is there a way to use a clamp-on meter or similar to get these readings when out on a job and I can't be unplugging things?

In a word, no.

In order to measure current with a clamp-on meter, you need to isolate the conductors. The line and neutral will cancel each other if both are passing through the clamp, because while the current is flowing left-to-right in the line, it's flowing with equal intensity from right to left in the neutral. The net result is zero.

The only way to measure without unplugging is to carefully strip away the jacket of the cord and separate the wires. The AHJ will not appreciate you doing this, and your client may not appreciate it if it's not your own gear. It's not real smart to use a knife on a live circuit, either.

If this is for a distro that YOU own and are setting up, you may be able to modify it with metering points (maintaining code compliance may be difficult), or just plug in Extech Line Splitters on each receptacle of the distro.
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Stephen Kirby

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Re: Measuring Current in Multi-conductor Wire
« Reply #7 on: February 05, 2016, 06:20:01 PM »

I have both the Extech splitter and a Killawatt.  I look at this as a kind of system characterization, not something to do all the time.  Either set up some place where you can open things up or go early to a large gig where you can do a bit of experimenting and characterize your max draw on each line.

I've also done a couple of tie ins where I had access to each conductor feeding my distro so I kind of know what my rig draws.
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Jeff Lelko

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Re: Measuring Current in Multi-conductor Wire
« Reply #8 on: February 11, 2016, 07:45:27 PM »

Thanks for the replies - I didn't see that I had so many!

Maybe you can try using a Kila-watt plugin and do the math.

Yeah, I already have one that I use for getting baseline consumption for various pieces of equipment that I own.  The reason that I'm trying to get 'live' measurements is that far too often I'm forced to share stages (and circuits) with other groups or bands that have no idea how much power their equipment draws.  They usually can't be bothered to measure their equipment either, so I'm just looking for a way I can do it for them and try to catch a problem before the power goes out! 

In a word, no.

In order to measure current with a clamp-on meter, you need to isolate the conductors. The line and neutral will cancel each other if both are passing through the clamp, because while the current is flowing left-to-right in the line, it's flowing with equal intensity from right to left in the neutral. The net result is zero.

The only way to measure without unplugging is to carefully strip away the jacket of the cord and separate the wires. The AHJ will not appreciate you doing this, and your client may not appreciate it if it's not your own gear. It's not real smart to use a knife on a live circuit, either.

If this is for a distro that YOU own and are setting up, you may be able to modify it with metering points (maintaining code compliance may be difficult), or just plug in Extech Line Splitters on each receptacle of the distro.

I definitely agree with all that, including not wanting to strip the insulation off my cables!  It sounds like using line splitters is the best way to go forward, at least for now.  Thanks for the input!

-Jeff
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Re: Measuring Current in Multi-conductor Wire
« Reply #8 on: February 11, 2016, 07:45:27 PM »


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