Clamp Meters

My concern was that this query is from a school student in a country with 240/440 volt system.
basically if you don't know how to work a clamp meter it is probably irresponsible for this site to try and explain, already we have seen talk about stripping off insulation and I know what is meant but if someone gets the wrong idea.........
Sorry to be a kill joy, I usually as irresponsible as the next man but I have a bad vibe about making these suggestions to someone with a clamp meter at school.

I agree, and shame on me for suggesting the "strip off insulation" technique without considering the audience.

Get the adapter suggested by Icewolf08!

ST
 
I may have missed it, there's so much good info in this thread, But did someone post the solution to the main question yet ? The trick with a clamp on amp-probe is to build a little jummper. Edison male on one end female on the other. connect everything together with 10-12 gauge single wires. thnn, or just the inside conductors from a standard cable. Plug the device you are checking into the female end and the male end into the wall, dimmer etc. This adapter allows you to clamp onto just one conuctor at a time. I have several of these in my tool kit with varying gauges of wire, and connectors. Obviously you don't need an adapter if you are chaecking the legs of feeder cable, but it's good to have a four wire setup and a couple of three wire set-ups. Remember when making the adapters, and using them, to use a properly rated connector and wire gauge e.g. don't use a 16ga wire on something you think might have 20 amps running through it, that would be bad.

Best way to test amperage is with a clamp meter. Given a clamp meter needs to surround one conductor (neutral / hot doesn’t always matter on single phase) one’s best way of doing this is with a commercially available figure eight clamp meter tool. Not only does it allow a reading but for a more accurate reading it allows for a x10 reading which once one changes the decimal point will more accurately read the current. This in a safe way.

This granted I have my own 208v jumpers for metering it and even three phase jumpers with wire between two plugs. Most often in doing this I would use type MTW wire rated for the amperage of the circuit and outer jacket further insulate the conductors to exposure by way of rubber or vinyl tubing over the conductor. While type MTW over stranded THHN wire has a thicker jacket and is more flexible, it still is not designed to be handled or exposed - further jacketing of the individual conductors than makes it a bit more safe.
 
My concern was that this query is from a school student in a country with 240/440 volt system.
basically if you don't know how to work a clamp meter it is probably irresponsible for this site to try and explain, already we have seen talk about stripping off insulation and I know what is meant but if someone gets the wrong idea.........
Sorry to be a kill joy, I usually as irresponsible as the next man but I have a bad vibe about making these suggestions to someone with a clamp meter at school.

I agree with this and it is a constant balance to be done on the website - this safety verses what is tech. Stripping away of or even percing the insulation and testing when not properly trained and supervised is a good note to make in not doing so.
 
Below is the PDF version of my study into various clamp meters if of help. Also the six meters that within pricing/quote for a bulk order and spec I thought were best.
 

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I rec'd my Fluke 336 today and it's great. Many significant improvements over the Fluke 30, besides being trueRMS. Only disadvantage is the jaws are only 1.25", as opposed the to Fluke 30's 1.5". Still should fit around any 4/0 feeder cable I encounter, (I hope). Advantage of smaller jaws is easier to get into tight places, which is seldom a problem for my use. I regret somewhat not spending the $40 more and getting the Fluke 337, which adds Hz, goes to 1000A (which I'd better never need!), and a min/max display.

I'll be testing the 336 against my 30 this weekend and will post the results.

Another word about safety, which cannot be stressed enough:
Here's the link to the Fluke meter's Safety Sheet PDF, applicable to all brands and types of Multi-Meters/DMMs, in 20 different languages!
 
So wouldn't you just know it, the first show on which I try my new Fluke 336 meter contains no dimmers, just lots of VL3000Spots, VL3500Wash, VL2500Spots, and LED fixtures.

The attached PDF shows the results of my Fluke Shootout readings. Note that these readings were taken during programming, with all lights on, but not necessarily moving, which would increase the power draw slightly. I could not see the stage from where I was taking the readings in the electrical room, so couldn't tell what was happening "at the other end" of the feeder, which was all brand new 4/0 by the way. Ah, that new feeder smell, almost as good as the new Leko smell.:grin:
 

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So wouldn't you just know it, the first show on which I try my new Fluke 336 meter contains no dimmers, just lots of VL3000Spots, VL3500Wash, VL2500Spots, and LED fixtures.
The attached PDF shows the results of my Fluke Shootout readings. Note that these readings were taken during programming, with all lights on, but not necessarily moving, which would increase the power draw slightly. I could not see the stage from where I was taking the readings in the electrical room, so couldn't tell what was happening "at the other end" of the feeder, which was all brand new 4/0 by the way. Ah, that new feeder smell, almost as good as the new Leko smell.:grin:


OK, no material differences. Now try it on a dimmer system set at 50% and let us know.

ST
 
So wouldn't you just know it, the first show on which I try my new Fluke 336 meter contains no dimmers, just lots of VL3000Spots, VL3500Wash, VL2500Spots, and LED fixtures.
The attached PDF shows the results of my Fluke Shootout readings. Note that these readings were taken during programming, with all lights on, but not necessarily moving, which would increase the power draw slightly. I could not see the stage from where I was taking the readings in the electrical room, so couldn't tell what was happening "at the other end" of the feeder, which was all brand new 4/0 by the way. Ah, that new feeder smell, almost as good as the new Leko smell.:grin:


OK, we're not letting you off the hook, here. Where are some dimmer readings?

:)


ST
 
I've had the same show with no dimmers in my building for a week now. And, in fact, is the first show I can recall that has not a single item made by ETC.:(

IF the show next week has dimmers, I'll post the new readings.
 
Derek, Did you get the cool tutorial/safety video with your meter? I have a VHS that came with mine. One instance shows what happens when a transient spike occurs as this guy is metering line voltage on a transformer. The result is a "Plasma Fire" a giant 10' ball of energy that just fries the entire electrical room. That vid will always do a good job of keeping you on your toes. :!:
 
Alas no video included with my meter. But I think I may have found that to which you are referring. Is it the CD/DVD in this link? VHS? What's that?:think:
 
Alas no video included with my meter. But I think I may have found that to which you are referring. Is it the CD/DVD in this link? VHS? What's that?:think:

Yeah. My Fluke is OLD, from pre-dvd days. When the pictures for the magic box came on a tape.
 
Derek, Did you get the cool tutorial/safety video with your meter? I have a VHS that came with mine. One instance shows what happens when a transient spike occurs as this guy is metering line voltage on a transformer. The result is a "Plasma Fire" a giant 10' ball of energy that just fries the entire electrical room. That vid will always do a good job of keeping you on your toes. :!:


This is the whole thrust of the new NFPA 70E standard for Electrical Safety in the Workplace. The current thinking is that arc flash provides at least as much risk as electrocution. The standard requires wearing various protective gear and non-flammable clothing when working on an open panel. These techniques were just not considered 5 or 10 years ago.

Part of the ESTA ETCP Electrician Certification exam is understanding the rules and requirements of NFPA 70E. I recommend that everyone get a copy.

ST
 
The current thinking is that arc flash provides at least as much risk as electrocution.

About time someone recognized that! Of the 2200 some shows I have done, and equal number I have helped on over the years, all of power related injuries I have seen or heard of involved burns, burned clothing, or eye damage from arc flash. (Excluding linemen stories) Yes, electrocution is a real and present danger at all times, but burns are far more likely due to what can happen with a simple tool drop. Although you have to be pretty unlucky to get nailed by a lightning hit or transient spike as Van described in the video, it is easy to deceive yourself into thinking everything is safe because you are holding a non-intrusive or insulated probe.

Fact is, once a panel is open (or in some cases the act of opening it), you are at risk. The saying in pyrotechnics is "Always treat explosives like they are about to go off." I believe death and injury are just as close when you are working with distribution. In fact, I have heard louder explosions from distribution equipment then most pyrotechnics can produce.
 
FINALLY had a show with dimmers. Three racks of Sensor 48x2.4Kw, driving 28x 1K-PAR64 6Lamp-Bars, 30-some single cans as truss warmers, 8x 8-Lights, and 8x 4552 ACL bars. Plus two 24-way Moving Light Distro's. All four services were 400A, with 100' of 4/0 feeder. One of the Sensor racks had a 1993 serial number! Below are readings taken with all dimmers at FULL, moving lights (34x VL3000s, Spots and Washes) moving all their motors; and all dimmers at HALF, moving lights lamped ON, but not moving.

Based on the data, it appears that: at FULL, the Fluke 30 is nominally close to the 336. However, with dimmers at 50%, the Fluke 30 UNDER-READS by about 15 to 30%: Consistent across phases in each rack, but varies from rack to rack. Notice that the neutral is approximately 1.33 times higher than any hot phase, hence the reason for the double neutral on Touring Racks, that I personally have never seen used, but might consider it if I exceeded 300A on 4/0 feeder.

I suspect the Blue phase of the 336 is a fluke, as it's really hard to take a reading while the numbers are jumping all over the place, basically watching the bally-hoo on the meter.

So as much as it kills me to admit it, STEVETERRY is correct.;) One must use a trueRMS meter to get accurate readings with a less-than-100% level, but the Fluke 30 is accurate enough at measuring total load. So I still have mixed emotions as to whether it was worth it for me to buy a new meter. I still think I should have bought the model 337.

On a different topic, this just arrived a few days ago. And one of my House Electricians didn't know what it was!
 

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FINALLY had a show with dimmers. Three racks of Sensor 48x2.4Kw, driving 28x 1K-PAR64 6Lamp-Bars, 30-some single cans as truss warmers, 8x 8-Lights, and 8x 4552 ACL bars. Plus two 24-way Moving Light Distro's. All four services were 400A, with 100' of 4/0 feeder. One of the Sensor racks had a 1993 serial number! Below are readings taken with all dimmers at FULL, moving lights (34x VL3000s, Spots and Washes) moving all their motors; and all dimmers at HALF, moving lights lamped ON, but not moving.
Based on the data, it appears that: at FULL, the Fluke 30 is nominally close to the 336. However, with dimmers at 50%, the Fluke 30 UNDER-READS by about 15 to 30%: Consistent across phases in each rack, but varies from rack to rack. Notice that the neutral is approximately 1.73 times higher than any hot phase, hence the reason for the double neutral on Touring Racks, that I personally have never seen used, but might consider it if I exceeded 300A on 4/0 feeder.
I suspect the Blue phase of the 336 is a fluke, as it's really hard to take a reading while the numbers are jumping all over the place, basically watching the bally-hoo on the meter.
So as much as it kills me to admit it, STEVETERRY is correct.;) One must use a trueRMS meter to get accurate readings with a less-than-100% level, but the Fluke 30 is accurate enough at measuring total load. So I still have mixed emotions as to whether it was worth it for me to buy a new meter. I still think I should have bought the model 337.
On a different topic, this just arrived a few days ago. And one of my House Electricians didn't know what it was!

Interesting to note that the delta-connected 208V Vari*Lites also show a wide disparity in readings between meters due to their switchmode power supplies that have a harmonic-rich current waveform. Note the near-zero neutral current (probably electrical noise), because VL PD's don't use the neutral. So, this would be a case where the equipment is "at full" all the time, and the only way to get an accurate reading is to use a true-RMS meter.

All in all, with the relatively small difference in cost between average and True-RMS meters, I recommend that anyone in the entertainment industry pony up for the right tool: the true-RMS meter. Just look at the numbers in Derek's study, and you'll see why.

I rest my case.

:)

ST
 
Interesting to note that the delta-connected 208V Vari*Lites also show a wide disparity in readings between meters due to their switchmode power supplies that have a harmonic-rich current waveform.

Switch mode supplies throw an even more interesting curve into the picture. Basically, power entering the supply goes through a full wave rectifier, a storage capacitor, then to a drive transistor (Usually a power MOSFET) which drives a transformer using PWM and FM to achieve a regulated secondary. The system accurately compensates for variations in line voltage by adjusting the current draw over a wide range of voltages. The thing that makes powering them interesting is that front end rectifier. As the diodes in the bridge only turn on after the input waveform exceeds the voltage stored in the capacitor, and turn off once the voltage drops below, the supplies only draw power near the peak of the waveform. Example, if the cap has a charge of 200 volts, no current passes from the supply line except during the portion of the waveform that is above 201.2 volts. (diodes drop about 1/2 volt.) The result is a current draw that is unlike any other. It almost looks like an abbreviated square wave with a rounded top. What this also means is that the supply must grab all of it's operating power out of a small portion of the AC waveform.

How does this affect us? Keep in mind that all of your switch mode supplies on a given phase leg are drawing power at the same time, and it is a multiple of what the wattage would suggest. Although cable heating is not an issue due to the duty cycle, voltage drop may be. In this case, the RMS ratings go out the window. A supply driving a 575w lamp may be drawing the RMS equivalent of 5+ amps, but in actuality, it is drawing 0 during most of the waveform, and 15+ amps at the top of the waveform. Three units may run just fine off of a 20 amp breaker, and clock in on the meter at under 20 amps, but during the critical portion of the waveform where the supplies are grabbing all their power, the actual load may exceed 45 amps. Again, this is not a thermal issue, but a voltage drop issue, and suggests up-gauging would be recommended.

In conclusion, I am not sure the industry has dealt, or even paid much attention to this issue. It is a well know problem on computer server farms due to the fact that computer supplies are switch mode as well. As the supplies generally work over a wide range of voltages, it may ultimately be a non-issue except with extremely long runs. One must always remember the other name for wire- Resistor.

NOTE: PWM - Pulse Width Modulation. FM - Frequency Modulation. Switching supplies use both, dropping the frequency under heavy load. As the old service saying goes, "if you can hear it, pull the plug! (but you're probably too late!)"
 
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... Three units may run just fine off of a 20 amp breaker, and clock in on the meter at under 20 amps, but during the critical portion of the waveform where the supplies are grabbing all their power, the actual load may exceed 45 amps. Again, this is not a thermal issue, but a voltage drop issue, and suggests up-gauging would be recommended. ...
Good point, JD. While I have never "three-fered" 575W Movers, I have, due to budget or laziness, "two-fered" them. But I don't like that practice because, if a unit needs a hard reset during the show, TWO units are lost while they recal and then, depending on the fixture and mode, must be "lamped ON" again. With this show, all of the 1200W VL3000s were single circuited, and the designer/programmer DID ask for a hard reset on one light during the performance.

Interesting to note that the delta-connected 208V Vari*Lites also show a wide disparity in readings between meters due to their switchmode power supplies that have a harmonic-rich current waveform. ...
Please elaborate, as the feeder is, of course, Wye-connected. Or are you saying "delta-connected" because the neutral is unused/unwired?

...All in all, with the relatively small difference in cost between average and True-RMS meters, I recommend that anyone in the entertainment industry pony up for the right tool: the true-RMS meter. Just look at the numbers in Derek's study, and you'll see why.
Well, who can argue with that point? But also look for features such as min/max, peak-hold, and though not as critical, but sometimes handy, frequency.

By the way, before anyone says anything about balancing the legs, I did not plan the patch. I believe the rule of thumb is no one leg should be more than 25% off from the others. I also feel it's somewhat of a moot point, as no one can guarantee that during every cue the legs will remain balanced. In fact, we're positive they WON'T remain balanced.

Another thing I learned during this exercise is how much energy a moving light's motors use, but again, it's a very remote possibility that every motor inside a light will be working simultaneously.

Others, please try this experiment for yourselves and post the results!
 
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I also feel it's somewhat of a moot point, as no one can guarantee that during every cue the legs will remain balanced. In fact, we're positive they WON'T remain balanced.

Interesting that you should mention that.... A bit of a tangent here, but I've been thinking lately, due to the nature of IGBTs one could design a dimmer system that actively remains in complete balance across all three phase legs no matter what the scene. To do so, the unit would use a master 3 phase power supply that produced a + / G / - buss output (much like a power amp.) Each IGBT PWM sign wave dimmer would the operate off the rails. No matter what circuits were loaded, the draw would be balanced on all three phase legs perfectly. I wonder if anyone is working on this?

end tangent.
 
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