Monitoring wires in with PV conductors

[don_resqcapt19]

Huh? "Cat5" isn't a wiring method in any chapter, it's an electrical specification for wire that's something else. Most Cat5 is CM, CMR or CMP.

But unless I'm missing something about Article 725, it's not a Class 1 circuit either. I mean, it's not even a Chapter 7 circuit.

So you are saying that these sensor wires are not covered by the NEC?

There has to be some confusion going on. This isn't a "power" circuit. It's also not "control" or "signaling". There is no "load". It's not a "communication" circuit, because there is no "communication". Prolly the closest thing to what y'all deal with on a routine basis is the output wires from split-core CTs. And I think that 725.136 D is what let's me put these cables in the same raceway.

The output wires from a CT are most likely Article 725 Class 1 circuits. All circuits are either power, communication, signaling or remote control circuits.
If there is no "communication" then what is the purpose of these wires?

725.136(D) does not apply to raceways.

 

[tallgirl]

So you are saying that these sensor wires are not covered by the NEC?

The question is where and how. It's counter-intuitive that these wires have anything to do with what's being described as Class 1, 2 or 3. PV wires -- definitely class 1. Wires between charge controllers and batteries -- class 1. Battery voltage sensor wires -- probably class 1, but only because they are sensing battery voltage and batteries, aren't the most "current limited" things in the world at the capacities we're talking about with solar.

I'm having a hard time wrapping my head around a temperature sensor operating on microamps as a "load" and the wires that connect the sensor to the voltage monitoring hardware that converts the output into a numerical value as a "circuit".

To me, "Load" and "Circuit" -- I can "do something" with that power. Turn a light on or off, run a motor, make a pot of coffee, annoy my neighbors with loud music, blanket the neighborhood with WiFi. A solar panel making 200 watts -- that's a source of "power" and the other end is a "load" and that's Class 1 "Circuit". A 1mm x 1mm chip of silicon as a photo detector -- not a source of power even if it outputs 3 volts.

The output wires from a CT are most likely Article 725 Class 1 circuits. All circuits are either power, communication, signaling or remote control circuits.
If there is no "communication" then what is the purpose of these wires?

That's the other thing -- I don't see how "power", "communication", "signaling" or "remote control" describe a wire whose purpose is to carry a voltage that is proportional to a temperature. It's not "power". It's not modulated in a digital or analog fashion. It doesn't turn on or off, or turn anything on or off, and it doesn't "control" anything.

725.136(D) does not apply to raceways.

Then I'm confused about how to read (A). And I'm even more confused about how some products even exist.

 

[don_resqcapt19]

...
I'm having a hard time wrapping my head around a temperature sensor operating on microamps as a "load" and the wires that connect the sensor to the voltage monitoring hardware that converts the output into a numerical value as a "circuit".

If they don't do anything why install them?

To me, "Load" and "Circuit" -- I can "do something" with that power. Turn a light on or off, run a motor, make a pot of coffee, annoy my neighbors with loud music, blanket the neighborhood with WiFi. A solar panel making 200 watts -- that's a source of "power" and the other end is a "load" and that's Class 1 "Circuit". A 1mm x 1mm chip of silicon as a photo detector -- not a source of power even if it outputs 3 volts.

I don't agree that those are Class 1 circuits...those are power circuits. For a motor the control circuit is likely a Class 1 circuit.

That's the other thing -- I don't see how "power", "communication", "signaling" or "remote control" describe a wire whose purpose is to carry a voltage that is proportional to a temperature. It's not "power". It's not modulated in a digital or analog fashion. It doesn't turn on or off, or turn anything on or off, and it doesn't "control" anything.

In the handbook commentary, it is mentioned that the output of a thermocouple would be an Article 725 Class 2 circuit. Yes I know that is just an opinion, just like yours or mine, but just putting it out there for information. It is my opinion that in general those types of sensor circuits are NEC Class 2 circuits.

Then I'm confused about how to read (A). And I'm even more confused about how some products even exist.

725.136(A) is the general prohibition from mixing Class 2 circuits with other circuits. (B) though (I) cover the details. The general rule in (A) prohibits putting the Class 2 circuit in the same enclosure as other circuits. The specific rule in (D) permits you to run the Class 2 circuit into an enclosure (note that this section does not use the word raceways) with other circuits where you have to connect the control circuit to the other equipment. An example would be the Class 2 control circuit to an outdoor air conditioning compressor. The Class 2 wires enter the enclosure and connect to the coil of the contactor that controls the compressor power.

The only way I know that you could be code compliant and install these sensor wires in with the power wires would be to use Exception #2 to 725.130(A), but the use of that exception would not permit the use of Cat 5 cable for the sensors.

 

[tallgirl]

Don,

I think that exception is going to have to be used regardless because of the issue you raised about the wires being damaged being pulled. It'll be cheaper to buy the cabling for the client (fixed price quote so I can have a reference system -- and they won't go up on their cost) than run more pipe on my own roof ...

Now for the next question -- anyone know a supplier for Class 1, 6 conductor cable? Part number? The solar power hardware hasn't been ordered yet, but I'd rather be prepared. It needs to either be UTP or shielded.

 

[gar]

101002-1707 EST

tallgirl:

Why does this CAT-5 cable have to go in anything?


For analog signals of the low data rate and reasonable voltage levels that you mentioned I do not see a noise problem with twisted pair wires. Even if there is some noise at the destination end, then simple RC filtering at the amplifier input will solve the problem. CAT-5 should be fine for your signal level purposes if not too long. You do not need a bandwidth greater than 1/10 Hz. The thermal time constant of the panel will be substantially longer than 10 seconds.

If you are interested in a different temperature measuring means, then some products I am working on that use Dallas 1-wire devices might be of interest. The communication is digital and multiple sensors can be strung on the same bus. Three conductors in one cable can handle many sensors. Maximum sampling rate is about once per 2 seconds. Some reasonable number of sensors on the same bus can be sampled at the 2 second rate. Temperature resolution is 0.0625 deg C in 12 bit mode, or 0.11 deg F, Response time depends upon the thermal contact with the medium being measured. With Teflon wire the upper temperature is above 100 deg C. Lower temperature is below -30 deg C. Maximum accuracy of +/-0.5 deg C is between -10 and +85 deg C. This is more a linearity and calibration specification, than a stability spec (repeatability).

Later I expect to have a current sensing device that will couple into this bus.

http://julie-world.mooo.com/doBar.php?chart=hour&width=640&height=300

Some questions on your Hourly Data Plot.
What does Inverter KWH mean? Is this the output power (energy) from the inverter?
What does Charger KWH mean?
Is this a grid-tied system?
Power usage seems to have a strange profile. Why is there very little usage above the base level?

Note: Since you use KWH at one hour sample points I can also read the graph as average KW without a scaling factor.

This is a quite different from the profile for my home. Overnight I have about 0.75 KW and 1.5 to 3 KW average levels thru the day and evening.

.

 

[hbiss]

I don't agree that those are Class 1 circuits...those are power circuits.

Don, you are correct. Although power and Class 1 require virtually the same Chapter 3 wiring methods, Class 1 is covered by Art 725 (which will refer back to Chapter 3), power is covered by all of chapter 3 itself. I should have said that the 1/0 conductors are power but for the sake of this discussion it makes no difference. Both require the same Chapter 3 wiring methods and are subject to the same restrictions with regard to different classes of conductors being in the same raceway and boxes.

-Hal

 

[tallgirl]

101002-1707 EST

tallgirl:

Why does this CAT-5 cable have to go in anything?

Because the client already rocked in the walls and I'm not in the mood to drill holes in anything to run it any other way. Also, it has to penetrate the roof somehow, and dittos for not being interested in penetrating the roof.

I sold one of their clients an older version of my monitoring gear and tried to up-sell them on more instrumentation. They countered with "we'll pay as much as we paid last time", which is sort of okay because I need a reference system. The goal was to get in and out for as little of my time and energy as possible. If their electrician can pull the sensors wires, and I just supply the cable, I get out cheap.

For analog signals of the low data rate and reasonable voltage levels that you mentioned I do not see a noise problem with twisted pair wires.

There is no "data rate". The device that performs the measurement provides 5VDC (and ground) and the sensor returns a voltage that is proportionate to the temperature. The return voltage is sampled every 5 or 6 seconds and then used to perform temperature correction on the array's expected output. See this page --

http://data.digitalgnomon.com:8080/?port=3&array=y

That's my array, though it is more "lab install" than "finished install". At some point I'll have to put pipe on the roof so I can put all those sensors AT the array. Need to reconfigure the array as well or else cut down a neighbor's tree ...

If you are interested in a different temperature measuring means, then some products I am working on that use Dallas 1-wire devices might be of interest.

I've looked at 1-wire and the issue I have is converting the 1-wire data into something the device that does the monitoring can read. Yes, 1-wire is a technically better solution, but the problem with 1-wire is reading it with the hardware that I have. Some day when my company has more money to invest in hardware development I might go that route. Or as I like to say, "Do you have $50K you're not using?" If any of y'all would like to invest in a company that can monitor the heck out of a commercial solar power plant, let me know. I use off-the-shelf parts, so my prices are lower than all of my competitors, and I'm very clever with software, so I'm able to add products much faster.

Some questions on your Hourly Data Plot.
What does Inverter KWH mean? Is this the output power (energy) from the inverter?
What does Charger KWH mean?
Is this a grid-tied system?
Power usage seems to have a strange profile. Why is there very little usage above the base level?

Inverter KWh is power from the inverters. Inverter output in excess of load is "sold" to the grid.

Charger KWh is DC output from the charge controllers to what is essentially the system's DC buss. The difference is conversion loss as well as battery "float loss". There are 25KWh of batteries at 48 nominal volts being floated and that can add up.

It's a "Hybrid" system -- works like a "Grid-Tie" system while the grid is present and an "Off-Grid" system while the grid is gone. The inverter outputs go directly to the main 60A sub-panel that feeds the interior of the house. The inverter inputs are bidirectional and backfeed the 125A service panel when "selling" and are fed when "buying".

The power profile looks like it does because my average load is a fraction of yours because I'm very good at greatly reducing electric consumption (and I sell this as a service with a money-back guarantee). The other reason is that the inverters only power interior loads, not the A/C compressor outside. So "Inverter KWh" ignores the A/C compressor. Not that it matters -- the loads really are extremely low. My "net" consumption is about 7,000KWh over the past 21 months.

Note: Since you use KWH at one hour sample points I can also read the graph as average KW without a scaling factor.

Yes, I'm very clever that way :grin: Do you like the way it changes each time you refresh the page?

This is a quite different from the profile for my home. Overnight I have about 0.75 KW and 1.5 to 3 KW average levels thru the day and evening.

That's because you likely waste a lot of electricity. And I don't mean that in an insulting way -- most people waste electricity for no good reason because they don't have their homes instrumented at all. I have a distributor (I sell solar power monitoring stuff internationally and consult with firms here in the US, Canada and parts of Europe) in South Africa who is making a killing reselling electric power monitoring devices. The pay-back period on something like an Envi or TED 5000 is usually measured in weeks to months. I sell "Kill-A-Watts" from a web page and people run around figuring out what is wasting power and what isn't.

I think I'd have to turn all kinds of things I don't need on to get to 3KW. My peak demand load, according to the PoCo's meter, is 5.5KW. And I live in Central Texas, have A/C, an electric motorcycle that needs charging, and typically have 4 or 5 computers, including a server running 24/7, along with two WAPs, cable TeeVee, several wide screen televisions, etc.

The key is actually using the electricity you buy, and not just buying electricity. A lot of people buy electricity they never use.

 

[LarryFine]

A lot of people buy electricity they never use.

I want to do the opposite.

 

[gar]

101002-2228 EST

tallgirl:

You do have a data rate on the temperature channel of about 1/5 Hz. Good filtering could be achieved with an integrator that was reset just after each sample was taken. If sample timing is not precise, then the duration of integration needs to be known. Or just use a simple RC low pass filter.

Your usage is about 4000 per year vs mine at about 14,000 per year. I have two large freezers, older ones, one large refrigerator, relatively new. I have 3 to 4 desktop computers and monitors on most of the time. Plus an 11 x 17 HP laser printer. My wife tends to leave lights on that could be turned off.

If I work hard I can reduce daily consumption to about 30 KWH, or about 11,000 per year.

I generally have no use for laptop computers and only use these when necessary. If all your computers are laptops, then your consumption will be much lower than mine in this area.

I have two TED systems, and 3 Kill-A-Watts. These are inexpensive devices, and my experience indicates quality problems with both. The TEDs are useful for looking at short time total usage and integrated usage, but have anomalies that are annoying, loss of communication or a malfunction somewhere.

The Kill-A-Watts have voltage range problems. The EZ version has a poor user interface, but has the advantage of no loss of data on power loss.

I can not see the Kill-A-Watt as much use to the average person relative to any possible great reduction in power consumption. It would be useful to evaluate refrigeration equipment if you had access to new devices to test. But, how do you do that without buying various models?

.

 

[tallgirl]

GAR,

I sell computers that run on about 1/10th what a typical laptop runs on.

As I said, I'm very good at reducing consumption. And I have a 13" x 19" printer, AND a electric motorcycle that takes 3.5KWh to "refill".

The key is knowing what you need to leave on, what you don't, and then going after the devices that waste energy. I went from about 14,500KWh per year 4 year ago to where I am now. The difference is that now I know what I use, what I'm wasting, and so on.

But also, getting rid of wasteful everything. My old 1250KWh per year fridge became a 445KWh per year one. My A/C went out -- both halves -- and instead of replacing it with a 16 SEER, I went with the 20.5 SEER. All the bulbs in the house are CFL, except the one in the oven, over the stove and garage door opener. The entertainment center that draws about 150 watts on standby is completely powered down when not in use, and it's on a circuit monitor so I can tell if it's on when it shouldn't be. The new standby power is 14 watts.

Gadgets like what these guys -- http://www.wattsupmeters.com/ -- sell are where the future is at.

 

[LEO2854]

GAR,

I sell computers that run on about 1/10th what a typical laptop runs on.

As I said, I'm very good at reducing consumption. And I have a 13" x 19" printer, AND a electric motorcycle that takes 3.5KWh to "refill".

The key is knowing what you need to leave on, what you don't, and then going after the devices that waste energy. I went from about 14,500KWh per year 4 year ago to where I am now. The difference is that now I know what I use, what I'm wasting, and so on.

But also, getting rid of wasteful everything. My old 1250KWh per year fridge became a 445KWh per year one. My A/C went out -- both halves -- and instead of replacing it with a 16 SEER, I went with the 20.5 SEER. All the bulbs in the house are CFL, except the one in the oven, over the stove and garage door opener. The entertainment center that draws about 150 watts on standby is completely powered down when not in use, and it's on a circuit monitor so I can tell if it's on when it shouldn't be. The new standby power is 14 watts.

Gadgets like what these guys -- http://www.wattsupmeters.com/ -- sell are where the future is at.

tallgirl thanks for the link that good info::grin:

 

[gar]

10103-1610 EST

tallgirl:

If you use a 1 megohm resistor with a 1 mfd capacitor as an input low pass filter, then the 3 db (half power point) bandwidth is about 0.159 Hz.

I took a quick look at the site you referenced. It is not clear what these people make, how the devices work, and how the systems are layout. The web site is very poorly designed. There is no summary information to provide a clear guide on the broad scope of what they make and an easily deciphered means to determine what a particular device does.

Do all units measure power, energy, voltage, power factor, and whatever else? I would have to go three of four levels down in the site to find this information. How do they communicate? What is the minimum AC supply voltage at which the devices should work? For example on one Kill-A-Watt unit I purchased it failed at about 105 V. Returned it and the next one was not much better. Is there battery backup to function during a major droop in supply voltage? Is collected information lost when power is lost? With the standard Kill-A-Watt data is lost on power loss. The EZ model is required if you want retention of data.

Are there two power measuring devices in each unit and two voltage sources or just one like TED uses? Is negative power displayed?

Just some of my reactions to the site.

That's the other thing -- I don't see how "power", "communication", "signaling" or "remote control" describe a wire whose purpose is to carry a voltage that is proportional to a temperature. It's not "power". It's not modulated in a digital or analog fashion. It doesn't turn on or off, or turn anything on or off, and it doesn't "control" anything.

It is a modulated analog signal. It is a steady DC carrier with AC modulation superimposed. And that AC signal has some maximum bandwidth that is most likely determined by the thermal time constant of the sensor assembly in combination with what it is attached to.

Now for the next question -- anyone know a supplier for Class 1, 6 conductor cable? Part number? The solar power hardware hasn't been ordered yet, but I'd rather be prepared. It needs to either be UTP or shielded.

You need twisted pair even if there is electrostatic shielding. At low frequencies a conductive non-magnetic shield has little effect on magnetic fields.

On your real time data why is your ambient temperature higher than the panel temperature?

Somewhere you asked about your real time data update. It is fine except at each update it shifts to the top and I have to scroll down.

Look at some of these Belden part numbers: 1269A, 82502, 82503, 82504, 83604, 83606, 85164. These are not all Teflon on the outside, nor all twisted. Teflon outer material might make it easy to pull after the main power wires are pulled. You can look for all sorts of possibilities at Beldon.com .

.

 

[ELA]

101002-1707 EST

tallgirl:

Why does this CAT-5 cable have to go in anything?
.

The goal was to get in and out for as little of my time and energy as possible. If their electrician can pull the sensors wires, and I just supply the cable, I get out cheap.
.

Or go one step further (when you decide to outlay for development) and use Power line carrier. Seems like a great application for it.
Then as you said the electrician's run your wire for you

 

[tallgirl]

Or go one step further (when you decide to outlay for development) and use Power line carrier. Seems like a great application for it.
Then as you said the electrician's run your wire for you

Hahahaha!

No, Power Line Carrier and solar don't work together well. There is so much RF noise it isn't funny -- especially around AC inverters. It would be more cost effective to go RS-232 over WiFi than for me to waste hours on getting PLC to work right.

The longer term solution most like is going to be Dallas 1-wire because its, you know, 1 wire (that's a misnomer -- it's actually 2 wires) along with the devices I'm using today. The other solution is to charge full fare and have a run of 3/4" EMT added along side the 2" for the PV conductors.

 

[tallgirl]

tallgirl thanks for the link that good info::grin:

Not at all a problem -- if I can get through some business-business I'll be set up as a reseller for their products, as well as putting together some automated power control software that borrows heavily from my solar power work.

Depending on how much you waded through that website, payback is measured in months to single digit years. There are also ways to create profit centers from power management that speed up the payback.

 

[ELA]

Hahahaha!

It would be more cost effective to go RS-232 over WiFi than for me to waste hours on getting PLC to work right.

Hahahaha!

No I was serious.
The source of the noise is very controlled and a "known" in this application, unlike in many other PLC scenarios.
Not saying it would be easy but wasting your time on RS-232 sounds about right.

 

[tallgirl]

Hahahaha!

No I was serious.
The source of the noise is very controlled and a "known" in this application, unlike in many other PLC scenarios.
Not saying it would be easy but wasting your time on RS-232 sounds about right.

I have 30+ years experience solving RS-232 and similar problems. The time was wasted years ago

But seriously, PV conductors are a very noisy environment and PLC products -- other than ones from companies with millions of dollars to spend -- tend to work poorly. The usual approach for PV monitoring is to use separate communication circuits -- often RS-485 -- for the monitoring data.

If there's something I'm overlooking, I'm willing to learn, but my experience, and that of colleagues, has been fairly negative.

 

[ELA]

I forgot to ask, what is RS-232 over Wifi?
I have heard of various digital communications protocols over Wifi and RS-232 as a hardware specification but never RS-232 over Wifi?

There are Power Companies working on using PLC to monitor smart meters remotely.
There challenge is much greater than a little 25Khz noise on DC feeders I should think. Again not that it is easy, just an attractive alternative if one were investing in development.

 

[tallgirl]

I forgot to ask, what is RS-232 over Wifi?
I have heard of various digital communications protocols over Wifi and RS-232 as a hardware specification but never RS-232 over Wifi?

There are Power Companies working on using PLC to monitor smart meters remotely.
There challenge is much greater than a little 25Khz noise on DC feeders I should think. Again not that it is easy, just an attractive alternative if one were investing in development.

There are PoCo's that deliver Internet access and "broadcast" radio over PLC. They also have bazillions of dollars to spend. I don't. The problems, as I'm sure you're well aware, are getting rid of the noise. And for PV, there are a lot of people who curse harmonics, because if a PV array were a musical instrument, it would be a harmonica

RS-232 over WiFi is RS-232 into Ethernet with a WiFi stuck on the end It's like RS-232 ... only there are no wires between A and B.

 

[gar]

101006-1940 EST

tallgirl:

Have you decided how to solve your problem?

Found a Belden part number, 88777, with 3 twisted pairs, and all Teflon. Might pull easily as a separate pull, especially if your DC wires are Nylon coated.

However, with the high current you mention at 25 KHz it might be better to have the data cable run separate from the power wires. As I mentioned previously a 1 megohm resistor and 1 mfd filter at the differential amplifier end might adequately filter the DC power cable noise.

Somewhat different subject. In Texas over a years time how many KWH of inverted output, in other words usable power, can you expect from a 1 KW array?

.