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Topic: network enabled home power monitor. (Read 6850 times) previous topic - next topic



People make simple typing mistakes every second or so, implying the OP did anything other than that when it came out "50Hz" is probably insulting to him (her, it).  And you're right, 110V is somewhat less dangerous than 220 but notice that the CTs are around the incoming mains at 240V with 200A available; I'd venture to guess that's more than most of the people arguing with me.  However, that's only a guess since I haven't seen their implementation.  And at any rate, any voltage that will overcome skin resistance is dangerous.  A 12V car battery will vaporize a screw driver and we don't worry much about it since 12V won't overcome skin resistance, but lots of people are burned working on them.

While it's true that there are differing local codes and that the codes have changed over the years, but I know for an absolute fact that every building code in the southwestern US requires a mains shutoff after the breaker and before the house wiring rails or the utility won't install the meter and the inspector won't approve the installation.  True, there are some old places that have screw in fuses left over from the 50s that may present a problem, that's why I said to look at it and decide.  And, yes waving a screwdriver around indiscriminately inside an electrical box is probably not a good idea.  Did I suggest that at some point?  Additionally, I don't remember saying, "just go for it". 

And, it's true that all current transformers don't just snap around the wires.  Don't buy those, buy the ones that snap on.....simple.

Lethality is something that can't be measured or predicted.  If I told him to drive to the store and get a part, isn't that potentially lethal?  Advising him to open the breaker box and take a look at what he's got could well be lethal, the door could come off and hit him on the head; especially if he has one of those boxes where the lid lifts up. 

Just telling him not to do it because the wording of his post implies inexperience is, in my opinion, not the way to respond.  I choose to respect the OP's intelligence and willingness to evaluate his own situation enough to offer guidance instead of alarm.


OK,OK, the OP DID ask for some advice, and he's getting it. Let's just discuss the subject and all learn something.

Anyone who looks at his service entrance panel and is not comfortable with how much they understand should find a friendly local Electrician to show them..

Most installations where I am (Vermont USA) have an outside-mounted meter and a main breaker right below the meter. That shuts off power to the entire building, including the input side of the service entrance. No notification to the power company needed... I was able to easily install a generator transfer switch ahead of my main service entrance panel using the wife-with-big-flashlight method.

Many/most service entrance panels have 3 or 4 inches of exposed Line1 and Line 2 conductors exposed at the top of the panel's main breaker and it's easy to add the clamp-around type current transformers on them.  Yes, there ARE exposed 115/230V (USA) terminals just below. No conductive tools needed or wanted in that area while attaching current transformers and their low-voltage output wires.

I think the more interesting issue is putting current transformers on some branch circuits with significant power consumptions; that's where the energy-saving is likely. And you can turn off the regular main breaker to de-energize them...

Regards, Terry King
...In The Woods In Vermont

Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info


From what I've read, Current Transformers fall into that dangerous category of appearing to be lovely and safe as they are non invasive.  They are just a transformer and come with dangers that come with that.  draythomp - please do a google search for "current transformer open secondary"


Yep, current transformers can be somewhat dangerous on their own.  They normally have a reverse ratio, one to many instead of the usual many to even less; that can lead to higher than expected voltages on the output limited by core saturation.  This would be the case if we were using un-burdened current transformers and there is a distinct possibility of blowing out the pins on a little Arduino if the burden resistor opened, or we opened it by mistake.  21st century current transformers made for monitoring power don't have this particular problem, their open circuit voltage is around 10 volts for a lot of them and substantially less when we put our own burden resistor on them.  That's why you test the thing on a mock up and don't go trying to build it directly on the power panel.

I have a couple of little current transformers on branch circuits to tell me when certain appliances are on.  These are not for the faint of heart to install.  You have to kill the power, disconnect the wire from the breaker, slip on the CT and put the wire back.  I usually kill the main and pull the breaker out of the box to hook one of these up.  My advice is different for these little things.  There's not nearly enough room to mess around with power on, it's too easy to have a screw driver slip messing around and it requires you get in there with metal tools that you could forget about and grab an exposed something while standing on a damp lawn.  Different thing entirely.  My method of killing the main is probably safe enough.

Turns out though that once you have watched power for a while you can tell which things are on.  My south air pump pulls around 4.6 KW and the north one pulls around 3.5, the pool pulls 2.8 on high speed and .25 on low.  The dryer pulls 10KW when the heater is on and the oven is around the same but with different characteristics, etc.  I thought the branch CTs would be useful, but I haven't looked at them in weeks.  I may eventually figure out a use for them, but right now, they're just there because it's too much of a hassle to take them out.


Here is a commercial unit that works very well!


As long as you don't touch any bare metal inside the panel you'll be fine, just be careful :-) ( perhaps wear rubber gloves )


About a year and a half ago I was all into the TED.  It truly is a nice device, but the expense for what I wanted to do was at the very edge of what money I could spend.  At that time they offered online graphing through a service that priced around U$25 a month as well as the graphing capabilities of the google stuff.  I tried to contact them about other online possibilities and they weren't interested so I eventually built my own.  Now, the google power stuff is being discontinued.  Seems there wasn't as much interest as google thought and the various utilities are so politically oriented that google couldn't get any meaningful contracts in place to handle them.  Hence my setup that is hooked to Pachube for online storage at about U$2.5 a month for back storage of a year's data. 

Turns out, I had a heck of a lot more fun doing it myself which is no surprise to anyone on this board, and after adding a number of other devices around the house, have spent probably twice what I was originally planning on.

Net, TED is a nice device, but check carefully into the longer term expense of storing the data (you WILL want to do this eventually) and be sure whatever interface they will be using in the future will meet your needs.  Also, since they are pretty closed on what code they are using and the various pieces of hardware, will they be around in a year or two to support you over the long term.


I'm not sure about the electrical laws in the US (or the UK) however there are two parts of your guidance that I would caution ANY reader with.
1.  In NZ and Australia, it is illegal to do any type of connection to a switchboard unless you are a registered electrician.
2.  The picture on your website shows the current transformers, with an exposed connection to the breakers just below. The good news is, that it's after the isolation switch.
3.  While your current transformer may be suitable, the insulation rating on the wiring leaving the transformer is not 110/230v rated and may not comply.

Now if there was a problem, and there was a fire, you could have insurance issues. This worries me more than a prosecution for touching the switchboard.
At the very least replacing the wiring with something with suitable insulation rating is good idea. (it needs to be double insulated and rated at 110 or 230v)

Personally the sensing of the meter is a much safer approach all round.



So far in most of the US, you don't have to be an electrician to hook into the house rails inside a power box.  You ARE restricted to not touching the wires from the main breaker up to the meter though.  That is reserved for the people from the utility; in some areas electricians are not even allowed to pull the meter to work on the system.  Seems people with grow houses (marijuana) hook in before the meter to avoid showing up on the billing system, so that entire area is off limits.  You can't turn off the power before the meter and you have to pull the meter before the main breaker to disconnect power, so the entire region before the main breaker is a bad place to mess around. 

You worried me a bit about the wires from the CTs into the rest of the circuitry.  I just looked at them and they have 600V insulation and they only carry around 3V under use and around 10V open circuit (internal burden resistors).  None of the wiring in the box has double insulation, just the usual 600V stuff you find on the ubiquitous Romex used everywhere here.  The CTs can't slide down the wire, that's why there's a plastic tie on them if that's what the concern is about the power lug below the CT. 

Reading the power meter itself is not a bad solution.  I tried that first.  I had an older meter that did not have the pulse output through an LED so I had to read the moving wheel.  The sun here is so intense that I couldn't sense the wheel accurately at all in the afternoon.  When I asked the power company about that, they said they had the same problem when they tested meters and actually pulled them into the shop to do measurements.  They also have a policy regarding other equipment attached to the meter.  You have to go through an approval process where you submit the device specs to them and then they come out and inspect the installation before they'll let you wrap a sensing device around the meter.  I asked them how long that took and they didn't have any idea; seems no one did it.  That may not be true now, this was almost two years ago.  If I could have made it work, I would have used the meter as my monitoring device and saved a bunch of headaches in building this project.

However, now I have a "second opinion" on the amount of power I'm actually using.  This resulted in me taking on the power company directly to make them prove I actually did have the peak demand they said I did.  It was a huge deal, the local utility commission was involved and the power company sent a person out to pull the meter and take it back for testing.  Of course, it was a total win-win situation.  They claimed the meter was reading correctly and I found that my peak demand numbers dropped to exactly what my CTs were telling me.  The new meter is nice, reads correctly and has a stupid pulse transformer on it.  Too late though, my other method works, so I'm not going to fix it.

The power company and the local building code inspectors have both looked at my installation.  There were some reservations from the building inspector regarding the arduino, but he took a meter and double checked to be sure it was all low voltage and said it was OK.  If I had had 110V exposed somewhere, he would have made me change it.  I called the home insurance people a month or two after it was running and they said, if it meets code, it's fine.  I'm actually safer from an insurance perspective on this device than I am with the extension cord I have running out in the yard.

Coding Badly

So far in most of the US, you don't have to be an electrician to hook into the house rails inside a power box

What about insurance?  If you make a mistake and burn down your house, will your insurance company cover the damage?


I'm sure there are jurisdictions where the local bureaucrats have restricted what one can do with the power into your house with some sort of law to further some political agenda or other.  That's exactly why I said 'most'.  It's really easy to tell though, call them and ask; that's what I did.

Where I live, you can mess with the power distribution yourself on any power input you own as long as you have it inspected by the building people before turning it on.  If you don't own it, the owner has to do it or have it done.  So, if it doesn't belong to you, get on the phone and check out what you need to do....simple.

Basically, it boils down to look at it, decide what you want to do and then start asking questions.  However, that depends on getting answers that actually tell you something.  "Don't" is not an answer.


Oh, good grief.  I haven't seen any sign anywhere that just says "Don't".  No left turn, Stop, etc, seen those but, don't is always followed by something else.  And, thinking about it, I've never seen don't on anything except a billboard advertising something.  "Don't" is what you tell a child on occasion and they immediately say, "why?"

Check out the second post on this thread, the one that set me off.  AWOL just said "Don't" and it was echoed later; no recommendation, no reasonable warning, no example; just, "Don't".  Forgive me if I choose not to insult the person asking the question first thing.  However, it doesn't seem to matter; the OP hasn't been back to comment or post further.  Maybe AWOL scared it off.


I just looked at them and they have 600V insulation and they only carry around 3V

You're quite right they have a rating, and they are suitable inside a switchboard or enclosure, however if they exit they should be double insulated ...just like normal power cords. (well down on this side of the world anyway)
The senario is that should the insulation become damaged, and make contact with the live bits, then somone could get a shock.
Drills and other electical appliances are double insulated, and if not, they have the metalwork connected to earth, in the hope it blows a fuse.

Here down under, low voltage wiring is required to be 50mm away from 230 wiring, unless there is a secondary barrier (additional insulation).

I see the odd renovation program that features the electical board and always wonder how come the wiring is exposed....
I seem to recall that unlike our 230v system, phase and neutral are floating with respect to ground.??

Good to see to sorted out the Power Company and their peak charging.



That's the big difference.  In the US, mostly, we can mix low and high voltage all over the place.  It usually is because different trades do the work.  The electricians come in with big drills and punch the stuff in, then the low voltage guys come in with smaller drills and do the same thing.  That's after the plumbers have put their stuff in.  The idea is that the heavier stuff goes in first so the smaller stuff can work around it.  Sorta works.  Now, it isn't a good idea to run a low voltage wire next to the power wire if you want to avoid crosstalk, and of course, they try to keep things separate as much as possible.

I like your idea of another layer of insulation though.  I can do this retroactively by sliding a sleeve over the wires up into the box and then pulling it up to the CTs.  I'll do that the next time I open the box.  It certainly won't hurt anything and could keep me from having to replace the wires at some point.  Although it isn't strictly required, it is a good idea.

Ground and neutral are not exactly floating.  Our boxes (the latest ones anyway) have a ground buss and a neutral buss.  The neutral (white) wires all hook to the neutral buss and the green (ground) wires all hook to ground buss.  Both busses are hooked to the metal of the mains box (what's up with that???).  The ground buss is hooked to a big ol wire that is hooked to a copper clad rod that is driven many feet into the actual dirt.  This is then distributed all over the house with the green wires hooked to the metal boxes as well as a ground lug on the plug itself.  The neutrals are only hooked to the plug.  Some of this doesn't seem to make sense, but when I researched why, there actually seemed to be good reasons for all of it.  I forgot the reasons over time, but it's easy to look up if you're curious.

Now that I understand what you mean by double insulated, it's a good idea and I'm going to do it.  Explain more about your concern regarding the exposed power lug below the CTs.  I may want to change something else.


Here we go again.  KE7GKP, notice that I said one could look it up if one were curious??  And, the question isn't what the code is, the question is why.  Once again, I'll look it up if I care enough, go down the street and ask the electrician that lives there or pick up the phone and call the local bureaucrat that handles that kind of thing.  Actually, I got curious and just did that.  The electrician tells me that the ground bar and rod into the ground is for lightning protection; this should be the ONLY connection to real dirt ground in the house.  All the other green wires connect to their respective panels (if you have subpanels) to a special ground bar and that in turn should only connect to the main box ground bar where the required disconnect is and the neutral-ground connection.  This is to prevent the lightning surge from traveling through several paths to ground minimizing the impact.  The exception to this is water features like swimming pools, they have special wiring considerations that are not relevant to this.

I don't know everything, don't profess to, but I'm willing to find out instead of just crying wolf for some obscure motive.  So far you have said that CTs can't be installed on branch circuits inside the box when that is the simplest place they are available and recommended by the people that make the TED, that the meter has to be pulled to kill power when the main cutoff is right next to the meter, that there is no non-invasive way of measuring current when the industry has been doing this for decades, cited laws that don't exist and now, you're starting to get personal with it.  Are you done with the personal attacks and misinformation?

Sorry to the other folks for this outburst, but sheesh.


We have no idea of the OPs capabilities. 

draythomp - you are obviously motivated to go out and learn these things and have a good grounding ( :* sorry) in the relevant subjects so that you know the right questions to ask in the first place.  I know lots of people who genuinely couldn't wire a plug.

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