Reading current

[HDSpokes]

800 amp 3 phase breaker, it has (2) 500 mcm wires connected to each lug, do i clamp around both wires or each individual wire for correct amperage reading. It makes sense to me even though there are two wires to each lug that both wires act as one wire is this correct.thanks

 

[waross]

Yes, clamp around both wires.
yours

 

[dpc]

If you can. Or clamp around each one and add currents together.

If you start feeling the urge to yank and pull on the energized cables to accomodate your clamp-on, don't do it. At least not without appropriate PPE.

 

[ScottyUK]

And make sure the jaws of the clampmeter fully close. An airgap in the magnetic circuit is the road to weird results and confusion.


----------------------------------

Sometimes I only open my mouth to swap feet...

 

[jraef]

That (air gap on a clamp on) can make a very scary buzzing noise that will clear the room of any non-electrical types. I know from experience!

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[dpc]

Good point, Scotty. I actually try to clean off the gap with alchohol or some kind of cleaner to get as good a connection as possible.

 

[itsmoked]

Nice tip jraef.. I will remember that for when I need it.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

Hi Kieth;
It may give a whole new meaning to the term "Clearing time".
Please post the results.
LOL
respectfully

 

[ausphil]

Dont't forget the flexible current probes that available and reasonable cheap nowadays. They work on the Rogowski principle and can be very useful for being placed around irregular shaped or multiple conductors.

They are quite accurate, and can be used with any decent voltmeter, as they give a voltage output proportional to the current they measure. Also the measureable currents can be quite high (in the high thousands of amps), which makes them very attractive for switchboard work.

Most power meters now give the option of flexible current probes.

 

[jraef]

Yes, plus Rogowski coils come with the added benefit of looking extra cool and high tech, which makes non-electrical types think you are more cooler than the last guy they saw checking current. I'm buying a new scope-meter and I am getting that option.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[stevenal]

While the burden of a clamp on ammeter may be small, I wonder about the effect the added burden would have on the parallel conductors if clamped around just one of them. Especially at light load, the effect of the meter may be to divert more current into the other unmetered conductor. The current splits in a manner that is inversely proportional to the impedance, and conductor impedance is also likely to be low. I believe the better method is to either clamp around both conductors, or to use two clamp meters simultaneously.

 

[ausphil]

JRaef,

I applaud your open and honest reasoning for choosing the Rogowski coil option - "they're cooler". I don't think engineers acknowledge that enough nowadays. There always has to be a technical and commercial justification.

As an aside, we needed to measure the current in transmission tower legs during an earth test, and during a playing around stage, noticed that you can actually series the Rogowski coils up to give you extra diameter, and still measure current. With 2 in series, the measured current dropped to about 95% of the actual current, and with 3 in series, it dropped to around 85% of the actual current. So if you need a larger diameter than a single coil, you can series them up, and if you don't need overly accurate measurements, then just read the output, or you can actually calibrate the readings and apply an offset to your readings for more accurate measurement.

 

[HDSpokes]

Thank you for the advice. I am using the flexible current probes. Really nice when you are measuring large diameter wires. Someone told me to measure both wires independently and add them up, but the distribution box that these are located in I couldnt get a mechanical clamp around but one wire as they are to close to each other with other loads being fed from the distribution panel. 1600 amp panel I`m not going to disturb them no more than I have too...thanks for the information