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Toronto, Canada
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Hi guys;

I have a question : Where it would be the best and safe location for a AC current sensor ( donnut type ) to monitor power usage of a typical home inside an electrical braker box ( picture is included in this post ) ?

I am not a pro electrician, I want to install the sensor safely and best way to get the total currents of the house.

I will built the sensor myself by testing it on a test jig and figure out the best numbers of turn for a 100 A reading and for a min of 1 A or less. The circuit I will build will be using op-amps for the signal "translation" going into the analog pin ( Vout from 0 V to 5 V ) .

Top picture : The AC sensor - A concept idea.

Bottom picture : The braker box. Big black wire : 120 into 100 A braker, big white wire, Neutral / GND


* Current_sensor.jpg (66.54 KB, 1024x746 - viewed 49 times.)

* electrical_box_North_American.jpg (164.28 KB, 1024x768 - viewed 53 times.)
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Phoenix, Arizona USA
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Is that white wire at the top or bottom of the box? Personally I'd put it in that corner area, then route the wires from the coil via one of those nearby smaller knockouts, with the wire surrounded by some spiral loom for extra abrasion protection (CYA mainly); securely attach the coil (wire ties?) to the white cable.

BTW - has this been inspected/approved by a licensed electrician and/or home inspector? What does your insurance agent say? I only ask (unless its not an issue/you don't care) because there is some regulation on including low voltage wiring with high voltage wiring (though I think it mainly applies to conduit runs and the like?). You might want to ask around, it if is a concern...?
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I'm not worried....   The only way something can go wrong is if an uninsulated part of the low-voltage wire touches an uninsulated part of the hot wire.

I don't know enough about the electrical codes to know what's "legal"...   But, I'll make a few suggestions to make it extra-safe.

If you are winding the toroid yourself, or if it's not already insulated, I'd fully encapuslate it with epoxy, RTV, or plasti-dip, or something.  Then, once you've got the hot wire inserted through it, use some zip-ties and/or heat shrink to make sure it stays in-place over the insulated part of the hot wire.   Basically just double or triple-insulate everything.

If you can wind the toroid with regular insulated wire, rather than enamel-insulated magnet wire, there is a better chance of the insulation staying intact.   But, I don't know if that's practical in your application.
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Toronto, Canada
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@DVDdoug

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If you are winding the toroid yourself, or if it's not already insulated, I'd fully encapuslate it with epoxy, RTV, or plasti-dip, or something.  Then, once you've got the hot wire inserted through it, use some zip-ties and/or heat shrink to make sure it stays in-place over the insulated part of the hot wire.   Basically just double or triple-insulate everything

I agree with this idea. And I will do that. I will use a lots of electrical tape.  But which big wire ? The white ( neutral ) or two on the big black wire ( live - 120 V AC ) ?  I am thinking more the big white wire. 

@cr0sh

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Is that white wire at the top or bottom of the box? Personally I'd put it in that corner area, then route the wires from the coil via one of those nearby smaller knockouts, with the wire surrounded by some spiral loom for extra abrasion protection (CYA mainly); securely attach the coil (wire ties?) to the white cable.

Your are seeing the top of the electrical braker box. The big wire came from outside - the electric meter.  And yes, the work you see was done by a pro electrician, BTW

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What does your insurance agent say?

What insurance ? It not even insurred !!  The house is being pay already, own by the person I live with for over 20 years has a family member, move to this place who his parents own first. And they don't want no stincking insurrance.

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because there is some regulation on including low voltage wiring with high voltage wiring (though I think it mainly applies to conduit runs and the like?). You might want to ask around, it if is a concern...?


That maybe a worry...  If I install it, it will be safe and a lots of insulation and black electrical tape.
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I don't think you know enough to make this safe or accurate.  The white wire is the neutral and only handles the load imbalance from the two hots.  You could have 100A on each hot (black wire) and read 0A on the neutral.  That is a single phase system and the two hots carry 240V between them.

If you must do this I would get prebuilt current sensors.  They make several kinds so make sure you understand what your looking at.  Some are voltage out, some are current out.  Each one must be terminated a specific way or bad things can happen.

I am all for DIY but please be safe and study this application in detail or you risk death or injury.  Maybe start with some smaller loads till you really understand the system.
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Left Coast, CA (USA)
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Bottom picture : The braker box. Big black wire : 120 into 100 A braker, big white wire, Neutral / GND

There are of course two big black wires and one big white wire shown in that picture. That is the common household feed used here in North America and is more often called "240vac split-phase" service.

 http://en.wikipedia.org/wiki/Split-phase

The three wires come from either a pole mounted or ground or buried distribution transformer, and they are the center-tapped secondary winding of the utility distribution transformer. Through properly installed circuit breakers the user can power either 240vac devices from black to black wires as well as 120vac devices using the white and either one of the two black wires. To monitor total current consumption on such a a system is not as simple as might first appear. Sensing just the common neutral conductor you would not be able to measure the current being drawn by 240vac loads connected only to the two 'hot' black conductors. Measuring only the neutral wire will only tell you the amount of current being drawn by all the 120vac loads.

So I suggest that you read that wikipedia link above to get a better understanding of the electrical distribution system used in your house and then look for proven (and hopefully approved) methods of user power monitoring.

 And once again, the standard response of "If you have to ask, you probably shouldn't be messing with it" still applies.

Lefty
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Measuring only the neutral wire will only tell you the amount of current being drawn by all the 120vac loads.

Just a quick correction, the neutral only sees the DIFFERENCE plus any harmonics that don't cancel out.

I also agree with Lefty, if you have to ask you probably should not be touching it.  What ever you do, don't remove the neutral under load.  It will let the 120V lines swing any where from 0 to 240V.  Light bulbs can blow, many electronic items will burn out in spectacular fashion.

Also even tho that panel is "only" 100A it most likely has the potential for thousands of amps at the lugs before the line fuse at the utility distribution transformer blew.  If you look at the breakers the main one is likely to be rated for 22,000A interrupt current and the small breakers around 10,000A.  Enough to cause an explosion.  More than enough to burn your eyes and skin with an ark and resultant molten metal.
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I am aware of the situation, guys... I respected your opinions. Safety First.  Open donuts ferrite do exists, so no need to move / remove and pplace back the big wires.  And a donut at the big white will only get the 120 line. And that will not measured the stove one, stove two, dryer and baseboard heater being on. I agree on that one.

If it is not possible to do, well... tought luck. But I will experiment on that sensor donut using a light buld to measured it current for calibration and readout of the sensor and see how it will work. Simple experiment to do, as long I respect and safe when using main.

Anyway, I am always safe when main is conserned. 
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I may choose to install a small current sensor at each braker. It is safer to remove a live wire protect by a braker. Just turn off the braker, remove the wire, place the donut sensor, place back the wire and turn on the braker.  Do that procedure for all the wires at the brakers. A 220 V line, just place 1 instead of 2.  In that way, I will have a current reading and wattage for each braker line, calculated the I for each line and do a total to find the total current and wattage.
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Never forget the lead-in wires are always energized, unless you call your power company to disconnect (yank the power meter).

It's too dangerous and too much hassle to make your own current transformers. They also have to have a dielectric rating to prevent any arc- which if that happened on the lead-in, it would be a bad thing, upstream of the 100A breakers...

I would buy two split-core CT's (i.e Leviton Ctd01-k16 $39), call the power company to disconnect for install and put them on each phase coming in (black wires).
Also, CT's need a burden resistor and without them they are dangerous and can generate many kV.

Google "Sub-metering Current Transformer" to find some.

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@prairiemystic

I agree with you. A close donut at the big wire ( entry of the house ) is out of question. A C-clamp type ( like an AC Ammeter ) will work.I need to look for them.  I did read this site about the current sensor design http://openenergymonitor.org/emon/node/59, a burden is need it in the design. I will design and test a close loop donunt type and test it by using a simple AC circuit. A AC switch, 16 gauge wire, 2 light bulb holder and 2 60 W light buld. I when to Canadian Tire to buy some of the parts... ( BTW, C-T have a sale on DMM , don't know about your area - in Toronto, yes )

And I know windding a ferrite with mag wire ( from a TV control coil ) is not going to be easy...  smiley-confuse

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Never forget the lead-in wires are always energized, unless you call your power company to disconnect (yank the power meter).

No power company, an electrician who need a EXPENSIVE permit to remove the Power Meter ( like over $500 )

BTW, I still need to buy a AC Ammeter with C clamp. I don't have it at the moment...     
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Think outside the box, put a sensor on the power meter and get accurate readings.   I started with a current transformer (you need a burden resistor btw, that never gets disconnected from the secondary windings, if you don't want a possible several thousand volts on the secondary) and became frustrated with the sometimes wierd readings it came out with (think poor power factor on power supplies etc).  Some from of optical sensor on the meter (phototransistor / reflective object follower) on the meter and time how long between pulses/disk rotations).  Accurate readings and no chance for frying yourself......  Nothing above 5V through high impedance loads.

Take a look :  http://pluggy.is-a-geek.com/index.html
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Interesting...The power meter is : outside and it is a digital type, no disk and no way to see or measured an output pulse of some kind. It is seal, lock and tag. 
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Since I did the write-up I've fitted my own meter downstream  of the 'official' meter because the official one runs backwards when the solar panels are running and the my system can't tell which way it is going.  Its a refurbished one from Ebay often fitted by landlords to sub meter to tenants - the vendor programmed it to read only one way..   If you're lucky you might find one with a built in photo-transistor you can wire straight to the arduino. Otherwise you just tape your own photo-transistor over the LED.  Your local electrician could probably fit you up if you want a completely safe job - it could be fitted downstream of your main breaker (presumably you have those over there) and be wired up in comfort.  Might be a tad more complex with the funny 240v/120v split systems you employ that side of the water.    

http://www.ebay.co.uk/itm/AMPY-SINGLE-PHASE-ELECTRIC-METER-ELECTRICITY-KWH-ENERGY-/350347365853?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item5192548ddd#ht_1418wt_907

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it could be fitted downstream of your main breaker (presumably you have those over there) and be wired up in comfort.

I don't think it is possible. The first picture is the Braker Box, the big wire came from outside. So installing that device is out-of-question.

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Might be a tad more complex with the funny 240v/120v split systems you employ that side of the water. 


Heh, It is our North American Electrical system.  smiley-wink
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