Energy Monitor w/ more than 4 CTs?

[dschoppe]

Hi,

I'd like to monitor energy in my home, but I have a rather unique electrical panel installation. See (large) photos here:

http://www.schoppes.com/BreakerPanel/DSCN1171.JPG
http://www.schoppes.com/BreakerPanel/DSCN1173.JPG

Outside the house, at the service entry, there is a 2-box panel. Power enters the left side (closed/locked in 1st photo) where Progress Energy's meter is located, and then flows into the right side (open in photos) through flat, uninsulated "bus" bars. A few large loads such as AC, future Hot Tub, etc., are fed from double pole breakers in this panel (visible in center of open side). Most loads in the house however are fed from two indoor sub-panels, and the breakers feeding these sub panels (125A and 200A) are connected in the outdoor panel as shown.

In order to monitor "total" energy usage, it seems I would need to put CTs on each of the wires to (or from) the 125A and 200A sub panel breakers (left side of open panel), plus the wires running from each single load break (AC, Hot Tub etc) installed in the outdoor panel.

I don't think it's possible (or legal) to install components in the left/closed cabinet, and there is no room (or safe way) to fit CTs around the flat, uninsulated bars where they enter the open panel at the upper left. There's also no way to de-energize the bars without getting into Progress Energy's side of the panel and probably pulling the meter head.

It "might" be possible, to measure total energy usage with 4CTs if I can fit large ones around the vertical section of the bus bars (to account for the single load breakers) and then put a second set of CTs on the wires to the 125A and 200A breakers (each CT wrapping two wires, same 120v leg).

Anyway, cost aside it seems better (and safer) to stay away from the uninsulated bars and install separate CTs on each breaker wire in this panel.

Are solutions available that can handle more than 4CTs to give total energy use? If not, does anyone have other ideas?

Thanks,
Don

[Pnord]

If you could find large enough CT's you could route the conductors through them after the breakers. You seem to have enough wire at the bottom of the panel and you could shut them off during the process.

What are the smaller wires coming off your 125 & 200 A breakers for?

[dschoppe]

If you could find large enough CT's you could route the conductors through them after the breakers. You seem to have enough wire at the bottom of the panel and you could shut them off during the process.

Thanks for the suggestion. Now does anyone know of "large diameter" CTs that could accommodate a bundle of wires, and that would work with TED, RFXPower, or some other setup?

What are the smaller wires coming off your 125 & 200 A breakers for?

My electrician's idea of a whole house transfer switch. i.e., turn-off the 125A/200A breakers to disconnect grid, and then connect generator at remote hookup box (which itself is at least protected by a another 50A breaker).

[Michael McSharry]

I believe the Wattnode can handle as many CTs as you wish as long as they are all of the same size. I use 4 CT in my setup and that priced-out in the mid $300 range. If your legs do not carry amperage that are in the same order of magnitude then the smaller lines will be in the lower 10% non-linear region and you will loose some accuracy on this branch. BTW, your site is returning page not found error.

[dschoppe]

Michael, thanks. Which model Wattnode do you use, pulse-output or LonWorks, and how do you I/F with HS?

This following text from Wattnode's site seems to suggest that I may even be able to obtain a CT to fit the bus bar (hopefully at least the vertical section to "consolidate" the single load breakers).

Our safe CTs, with integral burden resistors, produce a voltage proportional to the load current. At rated current the voltage is only 0.333 VAC. Split core CTs quickly install on existing wiring and solid core CTs can prevent tampering. Bus bar CTs are available in a variety of standard sizes, plus custom designs up to 10" x 10" (254mm x 254mm) and 4000A.

Also, I just tried my web page again, and it seems fine for me, both in Firefox and Explorer? If you still cannot access them, I'll try to compress the photos and post here, or send you them.

Thanks,
Don

[Michael McSharry]

I use the pulse output and 1-wire interface. Below is what I posted on cocoontech some time back that describes my design parameters.

I have been very happy with the unit. What I have noticed is that I have a 1KW floor from electronics that I have powered at all times. This would be things like the HS computer, routers etc. This means that I do not need to be too concerned about the non-linearity at the low end since I'm using a steady 8 amps which is well above the 10% of 30 Amps where accuracy would decrease. At the peak side I have never seen more than 4KW so this 30 amps (50 Hz into counter) is also well below my design maximum of 60 amps / 100 Hz.

I can see your pictures and the cleanest way looks to be 6 CTs. You may be able to straddle the lower ones and reduce your CT count to 4, but then it may be sized too large to reliably register on the upper wires. If you are not concerned too much about cost then you can have multiple interfaces that compute the power. Both RF (RFXCOM) and 1-wire can do multiple interfaces easily. It does get to be rather expensive this way, however. THe folks as Wattnode were rather helpful and could provide better guidance.

I had been looking for a few years for whole-house real time power measurement and settled on the Watt Meter as an effective solution. One of the hurdles that had made this task more expensive that I wanted to invest is the 400 amp service where I have 6 cables from the utility meter to the two circuit panels. For most of the available solutions this meant my cost was twice the standard 200 amp service because each solution could only handle 2 CTs in a split-phase configuration. With the Watt Node I am able to attach 4 CTs to the single Watt Node so my total system cost is one Watt Node, one Computer Interface and 4 CTs.

I wanted to have the ability to measure small variations in power use and wanted it to be very responsive so a real-time measurement could be observed. The Watt Node delilvers pulses proportional to the power being utilized and the pulse rate can be set to fit the needs of the application. My computer interface is a DS2423 1-wire device. For this device a 100 Hz count looks to be the practical maximum. My standard polling rate for the DS2423 is every 5 seconds, but can be accelerated to at least 2 Hz if I want to make some specific meassurements. This means I will be able to resolve 16 counts, twice a second, at average utilization. 20 amps / 16 counts = 1.2 amp/count/sample or 0.6 amp/second which is the equivalent of observing a light bulb operation.

While I have a 400 Amp service, my average utilization is 20 amps. While I have not measured peak utilization, I felt that allowance for 3x the average would be the appropriate max amperage that I would need measure. Since I run 2 CTs in parallel this means each CT will have a full scale measurement of 30 amps. The stated accuracy is 1% or 0.3 amps over the range of 3 to 30 amps.

This design tries to achieve accuracy and real time response. The 100 Hz Watt Node output frequency may be at the limit of the DS2423's capability, but the 33 Hz average should not be a problem. I suspect most users setting up whole-house power monitoring will use a much lower sample rate such as 2 Hz rather than 100 Hz and forego the resolution and update rate of the feedback. The DS2423 uses a 32 bit counter which means the computer has days to capture the counter value so even if the computer fails the DS2423 will continue to accumulate power utilization so longer term (i.e. daily, monthly) values should remain accurate.

The linear range of the 30 amp CT starts at 3 amps. This is a concern during the hours when power consumption is lowest and accuracy may be lost during this period. At the same time, the 60 amp peak may also be insufficient to handle simultaneous inrush current that may occur in certain situations. The low end problem will be much worse for those that size their CTs to circuit panel capacity such as 150 amps.

[dschoppe]

Hi Michael,

Thanks again for the excellent information. Besides the Wattnode Pulse-Output, I also spent some time looking at the Wattnode Plus for Lonworks, WattLogger software, and the Echelon LonWorks SLTA-10 host adapter. This would provide a very nice solution too, but at a much higher cost than the 1-wire / pulse count approach.

The simplest plug-n-play solution would still probably be a 400A (4 CT) TED and their new software. I need to find out if the inside diam. of their CT is large enough to straddle the 125A and 90A wires combined, leaving the other CT for the 200A wires (and possibly the 50A when we add the hot tub). Based on my caliper measurements this morning (on Christmas, you can tell I don't have kids ), the ID of the CT must be 21mm minimum.

200A wire diam: 15.25mm
125A wire diam: 11.6mm
90A wire diam: 9.4mm

Since the TED installation manual online states, "If your main service circuit conductors (wires) are larger than 1-inch diameter, TED Model 1000/1002 WILL NOT work.", I'm hoping wires up to 25.4mm will work. I emailed TED for details, so we'll see....

Don

[Michael McSharry]

The TED I had used a clothpin type CT that made install (and uninstall) very easy, but it also required more space since you need room for both the magnet and the clip. TED was an economical and easy install. The performance parameter that I did not like at the time was the update interval, but that may have changed with the new models.

[dschoppe]

Just a quick update on this...

I installed a 400A (4 CT) TED today together with the Footprints software and all seems to be working well. Measurement updates occur at about a 1Hz rate which is good enough for "active" monitoring, i.e., if an appliance or lighting load is changed, the display (and footprints) reflects the new figures within a second or two.

The footprints software appears to use both client (viewer) and server components, but I have not figured out if/how it is possible to run Footprints viewers on remote PCs which connect back to the server hosting the TED display unit via its USB interface. If anyone is doing this, or learns more about the upcoming TED API, please post it here or http://board.homeseer.com/showpost.php?p=800631.

Thanks,
Don

[telewizard13]

Looked at your pictures, BTW,The Itron electric meters have an IR LED on them that sends out kWh pulses. It is either on the top of the meter or on the front, depending on the model. I recently bought a Power Cost Monitor from a company called Blueline Innovations. They make a weatherproof, battery powered RF xmitter unit that clamps onto the outside of the meter (with a big stainless hose clamp,) and that unit has an adjustable IR pickup probe that captures the IR kWh pulses and transmits them (on 430 mHz) wirelessly to a companion LCD unit in the house. The unit in the house looks similar to a small LCD weather station. You enter your cost/kW (and time of day trigger points if you are "Time of Use" metered) into the unit and the display then shows the usage in kW real time and , based on the cost data you enter, it calculates and displays the cost/hour at your current useage rate, estimates your total electric bill in $$$ and shows the outside temperature (from the sensor unit) to boot! The outside sensor unit can also read the old style mechanical dial kWh meters. The sensor, when properly positioned, senses the edge of the spinning disk (from outside the glass case) and counts the black stripe every time it goes by. Perhaps someone smarter than me could buy one and figure out how to capture the kWh pulse and temperature data using a RFXcom receiver and use the data in HS. Not as fast as a CT setup, but you don't need an electrician to install it and have to spend hundreds of dollars for CT's or processing gear to get the data. Best of all, it's under $150 When you see what it is costing to run the lights or appliances in real time, it makes you seek and turn off things that are wasting energy. It has educated the wife to do that, as she writes the check to the electric company every month. It also helps to know what your bill is going to be in advance, as well. I have trimmed our usage by about 20% by having HS shut off things like the water heater , air conditioning and lights during the peak energy times.

http://www.bluelineinnovations.com/powercostmonitor.php

Rick Seaby
telewizard13