Thread: New To Me

It took me a little while to sort out what I was seeing. This was an all electric house, with about 300 amps of electrical capacity. The round device is some sort of transformer by GE that is used to record how much electricity is being used. The wires feed up into the meter. Once I realized that the incoming power was not routed through the meter, the light bulb clicked. Never saw this set up before.

Need a better way to bring photos in.

Just a CT setup for metering. Instead of measuring the whole amount a portion is measured and multiplied to get the actual usage.

Originally Posted by Jim Port

Just a CT setup for metering. Instead of measuring the whole amount a portion is measured and multiplied to get the actual usage.

Jim,

Is it just me looking at the photo on my phone, or do both line conductors go through the same CT?

I've always seen separate CTs on each conductor ...

Originally Posted by Jerry Peck

Jim,

Is it just me looking at the photo on my phone, or do both line conductors go through the same CT?

I've always seen separate CTs on each conductor ...

They do both go through. However, they go through from different sides, if that makes sense. One has power going left to right, and the other from right to left. It was confusing to me at first, but then it was pretty linear after I figured it out.

I am new to this metering arrangement.
This CT, current sensing transducer measures the RMS?
Is it still in use today or is this a vintage CT that has not been removed?
Any information would be greatly appreciated.
Thanks.

Originally Posted by ROBERT YOUNG

I am new to this metering arrangement.
This CT, current sensing transducer measures the RMS?
Is it still in use today or is this a vintage CT that has not been removed?
Any information would be greatly appreciated.
Thanks.

CT

Current Transformer

When ac current goes through the conductors, that current flow rises and falls at 60 cycles per second (called 60 Hertz ... unless the system if 50 Hz in which case it is 50 cycles per second ... or some other frequency), that current rise and fall creates a magnetic field around the conductor.

Run the conductor through a coil (circular core wrapped with wire) and you get a 'transformer' which creates voltage in the coil based on the make up of the coil (the number or wraps of wire around the core and other variables). The voltage output of that coil, like that of a transformer, is known for a given structure of the coil (number of turns/wraps of the wire, etc).

That allows a coil to have a know calculation, say 10-to-1 if designed that way. That means that 100 amps through the conductor creates 10 amps in the coil, the current in the coil can be measured as current or as voltage, but if we stick with current, then the current coming off the coil is 10 amps for every 100 amps through the conductor. 150 amps through the conductor is 15 amps out of the coil.

The meter now only needs to be able to read that 10 amps instead of the full 100 amps, and be calibrated so the output of the meter shows the same 10-to-1 difference, the meter reading reflects the calibration of the coil.

Current (excuse the pun ) technology which also has been around for a very long time (same forces at work which cause/allow a transformer to work).

That was a simplistic explanation of their operation, Jim Port will likely expand on the above and make corrections for clarity as needed.

I found this which might help: Current Transformer Basics and Current Transformer Theory

Nice easy synopsis Jerry.

Originally Posted by Jim Port

Nice easy synopsis Jerry.

Jim,

Thanks,

What do you say about the two conductors run through one coil, in the same direction or opposite directions as shown?

I've always seen multiple coils before.

I am not sure if they are trying to read two services with one CT or something else. I am not sure if it would work as an additive type metering.

Originally Posted by Jim Port

I am not sure if they are trying to read two services with one CT or something else. I am not sure if it would work as an additive type metering.

Kind of my thinking and wondering too.

If you put a clamp-on ammeter on a two-conductor lamp cord, it reads nothing as the neutral (returning) current flow cancels out the line current flow.

Likewise, if the two phase conductors were run through a CT from the same direction, I would think the reading would be the unbalanced current only?

CTs are supposed to be installed with the designated side facing the supply, so routing one phase conductor through the CT backwards, while it might offset the canceling out affect of the balanced load current, it likely would cause an off-calculation reading on that conductor?

As you said: "I am not sure if it would work as an additive type metering."

Originally Posted by Jerry Peck

CT

Current Transformer

When ac current goes through the conductors, that current flow rises and falls at 60 cycles per second (called 60 Hertz ... unless the system if 50 Hz in which case it is 50 cycles per second ... or some other frequency), that current rise and fall creates a magnetic field around the conductor.

Run the conductor through a coil (circular core wrapped with wire) and you get a 'transformer' which creates voltage in the coil based on the make up of the coil (the number or wraps of wire around the core and other variables). The voltage output of that coil, like that of a transformer, is known for a given structure of the coil (number of turns/wraps of the wire, etc).

That allows a coil to have a know calculation, say 10-to-1 if designed that way. That means that 100 amps through the conductor creates 10 amps in the coil, the current in the coil can be measured as current or as voltage, but if we stick with current, then the current coming off the coil is 10 amps for every 100 amps through the conductor. 150 amps through the conductor is 15 amps out of the coil.

The meter now only needs to be able to read that 10 amps instead of the full 100 amps, and be calibrated so the output of the meter shows the same 10-to-1 difference, the meter reading reflects the calibration of the coil.

Current (excuse the pun ) technology which also has been around for a very long time (same forces at work which cause/allow a transformer to work).

That was a simplistic explanation of their operation, Jim Port will likely expand on the above and make corrections for clarity as needed.

Thanks, Jerry.
I got a little off track.

Originally Posted by Jerry Peck

Kind of my thinking and wondering too.

If you put a clamp-on ammeter on a two-conductor lamp cord, it reads nothing as the neutral (returning) current flow cancels out the line current flow.

Likewise, if the two phase conductors were run through a CT from the same direction, I would think the reading would be the unbalanced current only?

CTs are supposed to be installed with the designated side facing the supply, so routing one phase conductor through the CT backwards, while it might offset the canceling out affect of the balanced load current, it likely would cause an off-calculation reading on that conductor?

As you said: "I am not sure if it would work as an additive type metering."

I think they are looking for leakage, that is, an increased flow thru one of the wires would indicate leakage to ground perhaps. When everything is right, the current flow is balanced and there is no reading.

I found this which explains it, so it's not just my WAG: "When measuring leakage current in a 1-phase/2-wire circuit as shown in the figure, the clamp meter should be applied around both wires. Because the current flowing to and from the load in the two wires forms a pair of magnetic fields that are opposite one another, there will be a difference in the two fields if there is any leakage current. The measured current value when the clamp meter is applied around both wires at the same time is the leakage current. Leakage current can also be measured by applying the clamp meter around a grounding (conductor)"

So why not just measure the neutral? Well this way they can read leakage that is not getting back to the neutral.

As for poking the wires thru in opposite directions, that shouldn't be necessary with alternating current. But maybe it is, so back away slowly and put the cover back on.

Originally Posted by John Kogel

I think they are looking for leakage, that is, an increased flow thru one of the wires would indicate leakage to ground perhaps. When everything is right, the current flow is balanced and there is no reading.

I found this which explains it, so it's not just my WAG: "When measuring leakage current in a 1-phase/2-wire circuit as shown in the figure, the clamp meter should be applied around both wires. Because the current flowing to and from the load in the two wires forms a pair of magnetic fields that are opposite one another, there will be a difference in the two fields if there is any leakage current. The measured current value when the clamp meter is applied around both wires at the same time is the leakage current. Leakage current can also be measured by applying the clamp meter around a grounding (conductor)"

So why not just measure the neutral? Well this way they can read leakage that is not getting back to the neutral.

As for poking the wires thru in opposite directions, that shouldn't be necessary with alternating current. But maybe it is, so back away slowly and put the cover back on.

Thanks John.

I am trying to get caught-up on CT seeing this is new to me.
Jerry, thanks for the transformer description. Much appreciated. Brings back youthful childhood memories.

Sorry to go off thread colleagues.
Father, an electrical engineer, use to explain how electricity worked. I can still envision the models he made for us, his siblings.
One such model was a crystal radio. We lived in rural Newfoundland when I was 10, 1964. Father was transferred as the electrical engineer to reopening a abandoned mine.
We had one TV channel. Walt Disney and Ed Sullivan were staples. Mother's brother, Vincent was on Ed Sullivan so that meant TV was a must. Father was told by Mother to make this happen.
In a rural setting, which we resided many times with father being transferred about every two years, radios communications were a way of being in-touch and getting local news, weather, and seeing whats happening in the world.
Father wrapped cooper wire around a paper cylinder while explaining crystal radios, turn-able coil, a capacitor, and we had crystal earphones from or battery operated radios. We lay in bad at night listening to whatever station we could find. Or Father using a thin flake of mica inserted into the bottom of a light bulb socket to make a light-bulb turn on and off. Magical moments of youth.
Thanks again, Jerry.


Back to the thread.
From what I have briefly read the wires should be in the same direction on a single phase.
The article is from Continental Control Systems LLC.
(Overview)
One current transformer (CT) can be used to measure several different circuits if all the circuits are powered from the same phase of the electrical service. This technique is useful when you want to combine a number of individual circuits into one measurement. It works best with smaller gauge wires that are long enough to thread through the CT. This technique can be used with a combination of single phase and three phase circuits.


(Measuring Multiple Circuits with One CT)
: All the circuits being measured with one CT must be on the same phase.
: All circuits must pass through the CT in the same direction—towards, returning to, the source of power.

Measuring Multiple Circuits with One CT | Continental Control Systems


Any comments would be appreciated.

Originally Posted by ROBERT YOUNG

Measuring Multiple Circuits with One CT | Continental Control Systems

They have good explanations for various wiring methods and needs, but none for running one conductors backwards through the CT.

Crystal radios - I built one when I was young, as I recall, I strung the antenna wire around the attic knee walls which enclosed the second floor rooms. I could listen to many stations from many locations, a bit staticy (spellin'?) at times, but I could still make it out.

Originally Posted by Jerry Peck

They have good explanations for various wiring methods and needs, but none for running one conductors backwards through the CT.

I thought it was covered.
Questions are underlined.
(Measuring Multiple Circuits with One CT)
1: All the circuits being measured with one CT must be on the same phase.
2: All circuits must pass through the CT in the same direction—towards, returning to, the source of power.
It begs the question/s.
a. Was there more than one CT?
b. Is this for their manufactured CT's only?
c. Were the 2 wires, that appeared to be in opposing directions, returning to the source?

Originally Posted by Jerry Peck

Crystal radios - I built one when I was young, as I recall, I strung the antenna wire around the attic knee walls which enclosed the second floor rooms. I could listen to many stations from many locations, a bit staticy (spellin'?) at times, but I could still make it out.

If I recall we used a loop stick antenna.
We would get radio signals from as far away as Fla, S.C., Even CBC radio.
Your needed a steady hand. You moved the rod across the coiled wires on the cylinder slowly. I would count the rises as the rod moved across the coiled wires from left to right to roughly remember were radio stations were. For the most part it allowed me to get close to stations that were clear.
As for staticy, very faint sounds. Maybe your antenna picked up ghost voltage. Just a hypothesis by the way.
Could be various reasons for reception static.

As for spelling staticy, Jerry you must have read what I created at times, ha ha ha!!! You'd think I was creating another language or even a code.