Author Topic: Connecting sets of CTs to 110 volt breaker in Electric Panel  (Read 3528 times)

drpulis

  • Newbie
  • *
  • Posts: 41
  • Karma: +0/-0
Connecting sets of CTs to 110 volt breaker in Electric Panel
« on: August 31, 2011, 11:31:07 PM »
I have 6 CTs connected to various breakers for monitoring, which dawned on me they are all breakers with black, red, and ground.

If I want to monitor another set of 4 circuits, that are all just 110V, with Black and Ground (white, and brass), how do I connect the CTs for measuring?  Do I just "set aside" the second CT connector?  OR, can I use the 2nd CT clamp to combine and monitor a different Circuit Breaker from its other clamp?
Started Installation/upgrade to TED Pro Home:  Nov 2014
 
  MTU1, NET, with 2 Spyders, Entire Main Panel
  MTU2, Generation
  MTU3, with 2 Spyders, Entire Sub Panel in Main House
  MTU4, 1 Spyder, Separate Cottage and Home Office

jrwalte

  • Jr. Member
  • **
  • Posts: 60
  • Karma: +0/-0
Re: Connecting sets of CTs to 110 volt breaker in Electric Panel
« Reply #1 on: August 31, 2011, 11:46:06 PM »
You should be able to connect them both to different breakers, but you won't be able to individually track them in Footprints. They would be summed and given as 1 MTU total. If both CTs are on the same phase, it may be an issue, but I'm not sure.

TEDSupport6

  • Sr. Member
  • ****
  • Posts: 291
  • Karma: +0/-0
Re: Connecting sets of CTs to 110 volt breaker in Electric Panel
« Reply #2 on: September 01, 2011, 12:02:11 AM »
You can either connect 1 CT and leave the other dangling (unattached) -or- use the other CT to measure another breaker. It would need to be a breaker on the opposite phase or else the readings from each CT will cancel each other out. Also jrwalte is right; you will only see these 2 breakers as one combined total in Footprints.

drpulis

  • Newbie
  • *
  • Posts: 41
  • Karma: +0/-0
Re: Connecting sets of CTs to 110 volt breaker in Electric Panel
« Reply #3 on: September 01, 2011, 12:04:57 AM »
You should be able to connect them both to different breakers, but you won't be able to individually track them in Footprints. They would be summed and given as 1 MTU total. If both CTs are on the same phase, it may be an issue, but I'm not sure.

Thanks, that is actually very interesting.  I have 8 circuit breakers that I want to monitor, and not looking deeply until now, I was going to put CT around 2 circuit wires.  Each of the breakers are sequentially one after the other, so they should all be on different Phase.  With what you are saying, I could connect one CT to one of the breakers, then the second CT to the next sequential (Phase), and of course to the associated MTU.  That is what I wanted for a Summed total on these anyway.  For instance, one breaker is "parts" of kitchen, and next one down is the Laundry and Wine Room.....one CT each, to one MTU.  If that will actually work, then that would be perfect for my situation.

I am just trying to add a second Gateway set of 4 MTUS (proposing total of 8 MTUs) in to the panel.  I realized these smaller location breakers are using over 30% of my electricity, and probably the Areas that I can call attention to the Family and gain most results to reduce electric usage.

However, getting 8 MTUs into this same panel may present a challenge.  I am considering putting the actual MTUs external to the panel in another weatherized Box alongside.
« Last Edit: September 01, 2011, 12:07:53 AM by drpulis »
Started Installation/upgrade to TED Pro Home:  Nov 2014
 
  MTU1, NET, with 2 Spyders, Entire Main Panel
  MTU2, Generation
  MTU3, with 2 Spyders, Entire Sub Panel in Main House
  MTU4, 1 Spyder, Separate Cottage and Home Office

rotus8

  • Sr. Member
  • ****
  • Posts: 315
  • Karma: +0/-0
Re: Connecting sets of CTs to 110 volt breaker in Electric Panel
« Reply #4 on: September 01, 2011, 12:56:49 AM »
You cannot have two gateways in the same panel unless you also add some filtering to isolate them from each other. You need one isolated group powering one gateway and up to four MTUs, and another isolated group with the other gateway and MTUs. Without this, the communications will interfere.

GAR

  • Full Member
  • ***
  • Posts: 131
  • Karma: +0/-0
Re: Connecting sets of CTs to 110 volt breaker in Electric Panel
« Reply #5 on: September 01, 2011, 05:17:22 AM »
110831-1947 EDT

drpulis:

There are some basic things you need to understand, and to explain these. I will refer to the entire panel as a 240/120 single phase supply. What this means is a power company transformer is supplied with single phase power and on the secondary is a center tapped winding that provides two 120 V outputs relative to the center tap. The sum of the two halves equals 240 V. You can use this as a 240 V supply to things like an electric dryer, or to 120 V loads like regular light bulbs.

When you make measurements on the secondaries relative to the center tap you find that the voltage on one side is 180 deg out of phase with the other side. Requires an oscilloscope to see this. A 180 degree phase shift means one voltage is upside-down relative to the other at any instant of time. These output voltages instantaneously are in the shape of a sine wave.

From a power wiring perspective there is a convention in the US that the center tap point is called the neutral, this will also be grounded. The two hot wires may also be called phase wires. Hot means substantial voltage relative to the neutral, ground, and the earth. The power carrying wires, the two hots and neutral, (conduct load current) are distinguished from a wire called the EGC (equipment grounding wire). The EGC wire will be a bare copper wire or one that is identified by green in some fashion. The EGC may be called the ground wire or grounding wire. Under normal conditions the EGC carries no current.

The neutral is grounded for safety and is a load current bearing wire, but under normal conditions has little voltage difference between it, the EGC, and physical earth. The neutral wire should not be called ground, even when it is grounded, because that causes confusion with the EGC.

Convention is that white is neutral, while black and red are hot wires. As said above bare copper or green is the EGC or a grounding conductor.   

To measure power to a load one measures the instantaneous product (multiplication) of the voltage across the load and the current to the load. In the simple form the TED system gets its voltage signal for this computation from the black to white inputs to the MTU. Then the MTU also has two current inputs from the two current sensors. Effectively the two current sensors are connected in series to produce an output signal voltage proportional to the instantaneous sum of the two input currents. The wiring is such that the two sensors are in phase opposition.

Here is where you could run an experiment and it might help you understand the effect of the sensor orientation.

Get a simple lamp with a 100 W incandescent bulb and a cord that is easy to separate the two wires in the cord. To avoid confusion do not bother with a 3 wire cord.

Note: Your current sensors do not have to be associated with the circuit where you measure the voltage. But your MTU voltage leads must come from the same circuit as the Gateway or RDU.

With both current sensors dangling in free space you should display a voltage reading and zero power (KW). Turn the lamp on and the power should still be zero. Put one current sensor around both wires to the lamp. Power is still zero.

Next put one sensor around one wire and the reading will be about 100 W for a 100 W bulb. Next put both sensors around the same wire with the dots in the same direction. The result should be near zero. Keeping the same orientation of dots move one sensor to the other wire. The result should be about 200 W. Next move both sensors to the same wire and make the orientation such that the dots oppose each other. The reading should be about 200 W.

Return to using a single sensor. On wire A of your cord, either one can be defined as A, put one sensor around wire A. Reading should be about 100 W. Reverse the orientation of this sensor, still on wire A, and the reading is still about 100 W. There is on special case of the settings where there would be a sign change when the sensor is reversed. My guess is that by default you won't be in this mode because in this mode I do not get any power reading in Footprints. Maybe there is a way but I have not found it.

Hopefully this kind of experiment gives you some feeling of some results of sensor orientation.

Now to your actual setup. The bus structure in breaker panels is such that in single phase panels the adjacent breaker positions are on opposite phases. This makes it easy to put 120 V circuit breakers in any location and any two pole 240 V breaker in any location.

Suppose you have two 120 V circuits from which you want the sum of the power being used. Use one MTU with its two current sensors to do this. If both circuits are on the same phase, then one sensor red dot has to point toward its breaker, and the other sensor has to point away from its breaker. If the two circuits are on opposite phases, then both sensors have to be orientated in the same direction relative to the breakers.

To test that your setup is correct turn one breaker off and read the power, and record the value. Next switch the off breaker to on and the on breaker to off. Record this power level. If either one or both were zero, then put loads on the circuits, and then do the measurements. After you have the individual power measurements for the two circuits, then turn both circuits on. The power read should be the sum of the two individual powers. If not the orientation of one sensor needs to be reversed. Or some other problem exists.

.

GAR

  • Full Member
  • ***
  • Posts: 131
  • Karma: +0/-0
Re: Connecting sets of CTs to 110 volt breaker in Electric Panel
« Reply #6 on: September 01, 2011, 04:43:36 PM »
110901-0822 EDT

drpulis:

Techniques for getting the total power from several circuits. These methods do not provide a way to get the power measurement from an individual circuit.

Suppose you have 4 circuits, all on the same phase, then the 4 wires can be run thru one current sensor, and leave the second current sensor dangling with no circuit thru it. This will sum the 4 currents and therefore the powers.

Move two of the circuits to the opposite phase. Run these opposite phase wires thru the second current sensor. Both current sensors have their dots pointing toward the breakers, or both the opposite way.

Same as previous paragraph. Two circuits on one phase and two on the opposite phase. Now use one current sensor with the other sensor dangling. Put two wires from one phase thru the sensor as above. The two opposite phase wires are run thru the sensor in the opposite direction.

To check any of these arrangements use the previous procedure of turning off all breakers to the sensor(s). Reading should be 0. One by one determine the power for each circuit by only turning on one breaker at a time. Next sequentially turn on all the breakers, and make sure that each breaker turned on adds to the power the amount of power from the load on its circuit.

.