Changing a "Smart meter" - 3 phase 

I'll try a technical explanation of why you can't open the secondary of a CT. The ideal operation is that it will force the proper secondary current: if it's 100 to 5 and you have 100 amps in the primary, it's going to do its darndest to force 5 A out of the secondary wires. Even if that requires a high voltage. And that high voltage can produce an arc, or break down insulation that was never designed to handle substantial voltage. The high voltage will also drive extra flux through the magnetic core and saturate it, which leads to spiky non-sinusoidal waveforms that can have even higher peak voltages, and can even mess with the power quality flowing to the load on the primary side. I also want to say that as an engineer and an engineering professor, I have learned a tremendous amount from this channel. Reminds me of when I first started as an engineer and was lucky enough to get paired with a very smart and experienced technician, who taught me lots of valuable skills.

I don't go very in depth on metering in this video... just kinda covering the "Lineman" side of things. Most Importantly - Make sure you have the proper meter. -Never leave an open circuit on an energized "CT" (current transformer). Lastly, I mention that you can't meter high voltage... you kinda can, but it's not practical. Any common high voltage meters (which many exist), use resistors, PT's or Ct's to reduce the values at the metering element. Cheers all! Be safe! 🍻👊

When I was in the industry (retired now) a very early teacher told us “ Electricity is a natural phenomenon of which to this day mankind does not completely understand.” …. I was instantly hooked, knowing I will learn every day and never be bored.

The difference with primary metering is that the customer gets to pay for the power loss in the stepdown transformer. I was the design engineer for a manufacturing plant that had four 2.5 MVA padmounts with a single primary meter. I enjoy your videos.

The other reason you need a PT is because the current isn't necessarily in phase with the voltage, nor is it necessarily a pure sine wave. In order for the meter to record real power, power factor etc. accurately it needs to measure the instantaneous current and voltage on each phase thousands of times per second. It sounds difficult but there are specialized metering DSP chips that do the measurement internally so the main processor just has to tally up the total usage and report it.

For large electric users ( like a steel plant ) I always picture a old glass mechanical meter the size of a 20 ft round swimming pool with the disc furiously spinning around. . .

The danger of opening a CT secondary when the primary is energized comes from the inverse relationship between voltage and current in any transformer. In this case, you only have the 5 amperes of current in each loop when the loop is closed, but break the loop and you now have the CT working as a step-up transformer. When working on the current loop side, you actually want to pull the right-hand lever of each pair first and close it last. I grimaced when you just went left to right like that when getting ready to swap the meter...

A HV primary metering tank is really nice for property security & power company employee safety. There’s only so many safety protocols/procedures you can be ready for and trained on in advance. Staying out of industrial property lets the power company set safety standards to keep their employees safe. Even excessive noise and vibration can be health & safety concerns. I always hate entering RF sites for data/comms handoff. I’m always happy when I can place my handoff outside of the main comms hut.

The peak demand metering is also used as a billing factor of the total power usage for the Billing period. Thanks for all the videos posted.

In Germany every (most)costumer has a 3 phase 400 Volt and 63 ampere. Use a costumer more than 80 amps, they use the same technique to metering like this video. But the transformer are more central and the wirering are underground. The hole neigborhood use the same transformer. The wires get in the last 40 ore 50 years from overhead to undergrund. Only 13kv and more are overhead lines. I appreciate your content. Greets from Berlin/ Germany.

From the very first time my dad explained to me the purpose of a screw-in fuse in our 100A residential fuse box in the basement, until I owned my first house, I have been fascinated with electricity and making sure I and others were safe around all things electrical. Now 63 years later, I marvel at your work and our local linemen who bring the power, especially after storms. You have my gratitude and prayers.

Had a New Smart Electric Meter installed about a year ago. Took Contractor longer to get out of truck and Open Box then to Pull the Old and Push On the New. 👍🙏

I really like all your videos. They're one of a kind and very educational . Thanks for taking time out to do these. I'm sure many people would agree. Thanks

9:32 - very well pointed out, the reason you cant leave a CT secondary open, is because of the magnetic flux that will be induced within the CT! It causes a spike in voltage and can surpase the ratings for any of the CT bushing insulation causing an arc. Keep the awesome videos coming!

Hi Aaron! About 52 years ago I received a BSEE degree from Newark College of Engineering (now New Jersey Institute of Technology). I worked in the communications business my whole career and started as an "Outside Plant Engineer" with NJ Bell so I never looked too far above the bottom 20 ft on the pole. LOL. I got a pretty good education on the theoretical side of power systems but never any hands on practical experience. I am totally hooked on your channel and can't thank you enough for sharing your real world experiences with us. I feel like I've learned more from you than I did in any EE course I took in college. Please stay safe and keep the episodes coming!

After 25 years in So Cal as an FSR, retired, I sure would like to have been watching your vids back then. In those days you really needed to press for info like you show, alot because on safety but, a guy didn't want to invest his knowledge unless you were serious. Thanks for what you do

You nailed it with not wanting to open CTs when they're live. I've seen the aftermath form some medium voltage stuff blowing. It's less that the current jumps up when you open them and more that inductive loads don't like changing how much current passes through them. So if you had 5A going through and you change the path from a copper wire to a few inches of open air the voltage can spike and either draw an arc at the switch or break down the insulation and energize the secondary side.

As a meter technician, I've had to correct some linemen mistakes like shunted CTs and reverse current flow on one phase. Needless to say, they can be some high dollar mistakes if improper metering carries on too long. Good stuff, Aaron.

I very much appreciate what you share. My rural home is supplied from a single transformer on a pole and your videos have helped me understand the technology. Thanks for the video.

I love seeing how other countries / companies do things. That is neat trick of using a shorting switch before removing the meter, so as to prevent a high voltage on the current transformer secondary. Occasionally we would get trainees and the rare apprentice for a week long visit for the experience and to 'assist', in the lab I was in. They were mortified when we kept shorting out the secondaries of current transformers (we could push through up to 2,000A on the primary). I had a small current transformer that was junk, but would always put on a good show, place it in the HiPot cage make the wires on the secondary about 15mm appart pass through a couple of amps on the primary and watch the sparks. I don't know how they were installed out in the field, but we used to get a number of current transformers back from the field with damaged insulation. Great video, Thanks.

Appreciate you linemen. We just went through a hurricane with plenty of power outages. Over 2.3 million customers right after the storm. Almost a week later and still 300,000 still without power. Quite a job.

It's great to see you posting again. I was an electrician with the USMC and we were trained to climb poles and deal with it. If we started falling from a pole we were trained to push away and hope for the best at the bottom . I hope you have all your family issues solved and you can start posting regularly again. Your videos are the best.!!!!!

Power systems engineer here, spent a good chunk of my career teaching. HMU if you want to go through the theory of why you short circuit CTs and why they make high voltage sometime. It could be a really good video on it's own.

I love watching your videos. I’m retired HVACR technician of forty seven years. When I first went to school to learn my trade one of the first things my instructor taught us was to never be afraid of electricity because it will get you injured or killed. Just always respect it and I never forgot that and I’m still alive today.

Awesome stuff Aaron we're just getting over a heat wave here in Las Vegas over 5 days above 115 one day couple days 120 deg, power is very important Hope your day is going well

I remember checking this channel years and years ago first like "Oooh this is all new and interesting" then as I have gone forward in both studies and experience the videos feel like the sort of conversations I have with colleagues on the job when we have 10 minutes to spare and it turns into story time

I appreciate you sharing your story. You have not idea how you have helped me. Thank you!

I came across a pile of PT's while wondering around the local utility's yard and was so curious why conduit with low voltage wireing was going up to a medium voltage head. This explains it perfectly, thank you!

Just wanted to say I'm another recent subscriber who randomly found your channel. I can't stop watching your videos because they're super informative! I don't work in the electrical trade, but I'm always trying to learn how the world around me works

The reason can't you open circuit a current transformer (CT), but you can open circuit a power is transformer is because a power transformer has winding on the primary side and CT does not (just a wire which is a single loop). As a result, the CT has an intern resistance that is very high, the power transformer has an internal resistance that is very low. From Ohms law V=IxR, so if the current is significant enough and the internal resistance is high - high current x high resistance = high voltage. A CT may see 400V or 800V or more. From Bobsdecline video, the CT test switch separates the currents by a very small distance (1/8"-1/16", 2mm or less). High voltages will begin arcing in very short distances, arc causes damage. Shorting the CT provides a low resistance, low resistance X high current = lower voltage.

The CT has the inverse winding ratio of a PT or other voltage transformer. So a single winding on the "primary" and multiple windings on the secondary. If the secondary isn't shorted or otherwise loaded in an energized situation, a very high secondary open circuit voltage will be created resulting in a shock hazard or potential equipment damage. (At least that is the explanation we got in the metering section of electrician apprenticeship.)

I absolutely enjoy your videos. I respect those power line from a distance.

Thanks for your video Aaron on primary metering. Excellent explanation on Ct's , Pt's, and all associated wiring.

This was great I always wondered how the large scale metering worked!

Rebuilt a metering tank (as you call it) for a local mill & another 1 for a golf course. 14,400 through & 110/220 out for the meter. 255 litres of Voltesso oil in it & it dripped for days. The phenolic plate for the meter connection had burnt through & need replacing. Hooked it backwards to test with a surge tester & made some awesome plasma balls with welding rods for arc points.

I am actually enjoying your channel. I happen to run across it and I think it’s very interesting. I had some family members. Of course I’ve passed on now but used to work for our local power company. In fact, one of the members of my family was a head lineman, so it’s quite interesting seeing what you’re doing

Now that was cool, it really is Rocket Science. Metering High Voltage with lower voltage, who knew.

from what i remember from school in January, open circuit on a ct will cause the voltage (or amps) to reach a dangerous level because its no longer grounded or something but all i remember is my instructor saying if there ever was a question that should get you failed instantly is saying "yes, open circuit on a ct is ok"

Thanks Aaron, that was really instructive. Stay safe.

I have always liked the description of Primary rate metering is that metering is simple " Sampling transformers step down the Voltage and the Current down to a level a self contained meter can read on all three phases of power. This metering can be set up for overhead to underground lines like you show in the video. Or Overhead primary to overhead customer owned system. The metering for the customer owned system would be the same. The size of the metering transformers would be based on the customers expected load. Great video.

In a short circuit the voltage is close to zero. The CT is a transformer with a winding ratio with current in mind. The meter's relatively low resistance shunts the voltage close to zero. It is the current in the circuit that is measured. With the CT open ,not connected to the meter's low resistance, you have the potential of the winding ratio of the CT on the high line.

Looks like some meters we use in the US as well. Some buildings I worked at had different 3 phase meter. some of the 480V service ones have dual displays . the second display is demand . I seen 208V 3 phase with that same type meter .just different brand . the old meter had the dials and the 480V one had 2 sets of dials . I was working at time of meter change to see the newer meter go in.

Great explanation on metering and associated replacement, find your videos informative, thanks!

thanks for sharing this was very insightful, I am working towards becoming a lineman.

The way you explained seems that the ratio of the transformers can be tuned on the unit. As they are probably hard to inspect, how do you guarantee that the customer doesn’t mess with the CT ratio directly on the transformer in order to pay less for electricity? Thanks for the videos! As an electrical engineer that doesn’t work with high voltage, I learn a lot from them.

Interesting set up to meter a 3 phase service.

Neat stuff. I always wondered how they meter those multi-megawatt installations without melting the meter.

My understanding is smart meters have a built in cell phone. Driving around you will notice some transmission towers have cell antennas mounted on the sides. Some substations also have cell antennas. Your meter reports to the nearest substation or transmission tower. This is how the power company knows instantly when your neighborhood has a power outage. They also know which circuits are out and can instantly reroute power around the outage. I remember the old days not too long ago when customers had to report power outages themselves. Then wait while the crew drove around looking for the problem.

Nice work Aaron, I like the color code you guys use. I've been pushing my company to use a similar color code. One thing I do is mark phase rotation in all my 3 phase meter boxes. Knowing the rotation comes in handy during transformer changes and storm restoration.

Aaron you know more about electricity than our new generation of electrical engineers......😂😂😂😂😂 Keep up the amazing work!!!!!🙏🙏🙏🙏🙏

Bro, you are a rock star! Your knowledge is impressive.

Awesome explanation! Thank you

Thank you for another great video.

Interesting information

I find this stuff very interesting, so thanks for this content

Good info from Germantown Wisconsin

Thanks Arron 👍👍👍

6:37 you can see the CT is a multi ratio either 100 or 200/5. Those are chosen based upon the taps used on the secondary side of the ct ie x1-x3 or x2-x3.

Always interesting seeing the wire colours other countries use. Here (New Zealand) three phase is also red, yellow and blue, but neutral is always black. Single phase is red and black. Most appliances though have the European colours (brown and blue), so another set of colours to remember. Not sure how we do industrial metering like in the video, the only three phase meter I’ve seen was wired similarly to a residential meter (inline) as it was essentially a retail store, so no heavy loads except for a roller door. I believe the door was the only three-phase circuit, everything else was divided evenly across each phase.

My relative has a house with 3 phase power. 3 600 amp breaker panels and enough Air conditioning to keep the house cool, and in SC it is over 100 degrees 6 months out of the year The electric bill is 4000 a month

I'm not any kind of electrician or lineman. But, can still learn something. 🤝 🍻

greetings brother lineman from flagstaff Arizona 👊 🇺🇸

That is basically how we meter the two 13.8kV feeders into where I work, only difference is the CTs and PTs are mounted in the main switchboard..

10:30 so THAT is why the boss had me to flip all of the switches in the box outside at 12:30 am, he said it shut off the windows 95 computer running the business, joking!!

Hey Aaron, I came across a coax drop today that was melted nearly the WHOLE length from the house to the tap (fairly long with a midspan) Customer said it was smoking yesterday! Since we aren't supplied amp clamps, I was concerned it was a serious problem, so I called MB Hydro to be safe. A guy showed up maybe 20 min later with a bucket truck, but didn't seem too concerned. He pulled the meter, ran some tests and said everything's showing good. I felt really dumb cuz I fully expected for him to find an open neutral! I then asked if I could cut down the melted drop from the house while he was there, just in case. Nothing. No sparks etc. He changed the crimp on the neutral at the weatherhead just to "do something" and trimmed some large branches near the pole after talking to another neighbour. Anyway, he said he'd hang around while I changed the drop. I asked if his tests would indicate an issue with the neutral from the panel to the meter, and he said no, that's not his problem (understandable.) Their internet came back up, so I asked them to try their oven and dryer for a few min. I also said if the drop melts again to call an electrician. I was so worried that cutting the old drop could've started a fire. The troubleman said he's seen some strange things with open neutrals but not a drop melted that bad. Sorry for the long message. Just curious what your thoughts are, and hopefully we get to see a video on this topic soon. Thanks!

Just FYI, for your safety. In this video you did open circuit the secondary of the CT for a short time. You should always open your shunts (polarity - the ones that catch and short to neutral) before your returns. By opening the returns first your polarity has no return path until you opened the next switch in line shorting it to neutral.

An open secondary on a CT will cause it to produce a very high voltage, usually high enough to damage the CT and high enough to be a serious hazard.

CT without a Burden (AKA the meter ) will produce a high voltage across it . And can arc through the windings of the CT and destroy it .

Great video, thanks

Love the videos man

Love the channel!!

It's not muddy, but it's a bit foggy for someone like me. I can now understand the different applications for three phase metering. Larger businesses and farms could have different meter options. Thanks for the info. Stay safe, and God bless

Hi Aaron, I sent your hearing protection to you by UPS ground. Not sure when it will arrive? Keep an eye out for it. Great video! We have a separate metering department. We don't have any training on it. Thanks for the tutorial though. We have those overhead metering units for very large customers only. I thought I noticed a hole in your left "keeper" or gauntlet? Better check that out. I don't want your rubber glove to get a hole too. I know you check your rubber gloves & sleeves daily 😉. Keep up the great content! I hope everything is alright? Thinking of you & your family.

Seeing that meter, all I could think was Marathon Man: "Is it safe?"

Those wing nuts could have fallen down across those HRC fuses to the left, when you undid them. Those HRC fuses need a plastic cover to stop that happening.

Howdy Aaron. Always enjoy your content as I find your particular world very interesting. Keep up the good work and stay safe! Oh... got a question for ya... why the name of "Bobsdecline"?

There isn't really any difference between a current transformer and a voltage transformer, its just the way that they are used. A current transformer is just one that has a very low resistance burden connected across its secondary winding and it usually has a very high turns ratio. The primary might have say one turn and the secondary 1000 turns. In normal use the low burden resistor allows sufficient secondary current to flow to cancel the primary current with only a small voltage across it and an even smaller voltage is reflected to the primary. So the presence of the CT has negligible effect on the load circuit. If the secondary circuit is opened then it ceases to be a CT and becomes a voltage transformer and just like any other voltage transformer it will try to generate a secondary voltage that is the turns ratio times the primary voltage. So in this case if the primary is say 7kV then it will try to produce a secondary voltage of 7,000kV. This is sub optimal.

Just wanted to pass on to you that there cartridge fuse covers in stores that covers those fuses and holder so you don’t drop something across it and cause a short.Made of plastic and clips on. All new installation should have them.

In most places where smart meters are used, there's a charge on the bill for peak power usage.

Bring the spinny wheel back on meters

Regarding the current transformer, if it is essentially an AC current source representative of the customer load by some fraction, then it is designed to be connected to a very low impedance, as in the power meter. With any current source, the output voltage equals current times resistance. An open circuit has very large resistance, so the output voltage will also become very large. The open-circuit voltage will rise until it arcs over, or finds some other path through parasitic capacitance in the transformer windings, for example. Whereas voltage sources don't like short-circuits, current sources don't like open circuits. I'm not familiar with CTs, as such, but the electrical theory should be the same. Please correct me if I missed something!

I wonder if the disconnection causing an arc thing is because the CT is basically an inductor, which is something where if the power is pulled off, the voltage spikes. You use diodes (I think?) across the inductor to clamp the voltage spike.

What model of phone have you got? The zoom is great.

FYI if the red and black tape was supposed to block the # you can clearly see on other angles

But did that meter ever finish booting?😂

Unhooking a CT leads will turn it into a fly back transformer and create very very high voltage, 10000s of volts

you forgot to screw the Plexiglas cover wing nuts back on :)

U stay SAFE ~~~~~~~~~

Excellent info. Thanks for posting! What is the volts rating on those gloves that you are using and how often do you retire them for a new pair?

I'm sure you get this question all the time: Are the new digital/WiFi-connected smart meters more "efficient" at detecting residential usage, say by compensating in real time for different Power Factor values? I know a guy who used to keep his bill artificially (hence, illegally) low by adding capacitors to his home's wiring. And, if the answer is essentially "Yes", do you give any credence to consumers yelling about their bills going "Up", "Way Up", even "2-3x Higher" after the upgrade??

5:02 the audio is crisp

I watch these.. and go "damn I really should switch fields" but I cannot afford to apprenticeship for $18/hr again. Guess i'll stick with automotive...

I wonder if ‘safe’ on the meter is the built-in diagnostics detecting a problem and going into a safe mode.

On 3-phase meters, the self-contained types will usually have five or 7 lugs. Transformer-rated types will have either 8 large lugs or 6 large lugs and a row of smaller lugs (that's the the first time I've seen a transformer-rated type with only 4 of the 7 smaller lugs fitted; the three 'missing' lugs were for an external demand meter in the old days - before the advent of microprocessor-based meters).

DYMO labels ... been a while!

Yea, pull one out, plug one in.

Good deal Aaron.......

Aaron, can you cover Ferroresonance in one of your videos and if you have ever ran into it? I know you can isolate the meter by opening the cutouts, but was curious if ferro could be an issue on a tapline like this.

On a power pole no less,

Considering how inexpensive, accurate, reliable and easy-to-deploy clamp-on ammeters are, why don't electrical utilities come up with a way to meter customer usage with amp meters instead of inline devices like the ones you're showing?