[HH] instrumenting a breaker box

[Tom Metro]

Greg London wrote:
> Was looking to instrument the circuits in my breaker box.

What are you looking to sense? When current is flowing through a
breaker? How much current? How much voltage? Both?


> The only thing I could find commercially was this:
> 
> http://www.theenergydetective.com/

There's also one of these:
http://www.bluelineinnovations.com/

I bought one years ago for some trivial amount when NSTAR was
subsidizing the cost, and unfortunately never got around to installing
it (which I still should), so I can't speak to its effectiveness.

It has a consumer-friendly sensor that simply clamps onto your
electricity meter and optically monitors the spinning wheel or digital
display to track power usage. (Seems rather inefficient when you can
probably get that info directly from the meeter with a bit of RF
hacking, as the new meters can be talked to wirelessly.)


> But that only instruments the incoming circuit...

I'm pretty sure one of the newer startups doing this claimed that with
some analysis of your usage patterns, they can figure out how much power
is going to each of your major appliances, despite only having a whole
house sensor. Seems a lofty claim. Or maybe they were just claiming that
after a learning period, they could tell you which combination of
appliances were running at any given time.


> (200 amp service, 40 circuits)
> ...and getting enough sensors to do all the breakers
> could cost close to a thousand dollars.

A current probe for a multimeter will run you about $40:
http://www.amazon.com/Current-Clamp-Probe-for-Multimeter/dp/B00NRHB5PM/
http://www.righttoolusa.com/p/Tpi-A250-Ac-Amp-Current-Probe-Adapter-400a-For-153-163-183-183a-And-31258602.html

which would add up to $1600 for 40 circuits just for the probes.


> Seemed expensive.

Like Drew said, probably pretty reasonable for a code compliant solution
that you can install yourself.

Code-wise, there's probably more flexibility if you are installing the
probes outside of the main breaker box. Something you'll want to
consider if you go the more D-I-Y route suggested below. Obviously the
probes are low-voltage and electrically insulated from the power wiring,
 so they are low risk. The challenge is that the probe needs to be
placed over the hot wire only, so you can't just clamp it onto the romex
cable in any old spot. Splitting open the jacket at a mid-point would
undoubtedly be a code violation, but you could do that inside a small
work box. Consult an electrician.


> Anyone know of a cheaper way?

You can easily find multimeters with integrated current clamps for as
little as $12:
http://www.harborfreight.com/digital-clamp-on-multimeter-95652.html
http://www.amazon.com/Meter-Multimeter-Digital-Clamp-Probe/dp/B00E6NDZ22/

(That a probe alone cost $40 and a probe + multimeter only cost $12
probably tells you something about the relative quality.)

But you'd have to do a lot of hacking just to get the mechanics to work.
And that's before you build whatever is necessary to process the signals
from all the probes.

It looks like there are some lower cost current probes made for home
automation:
http://www.amazon.com/s/ref=nb_sb_ss_c_0_14?url=search-alias%3Delectronics&field-keywords=current%20sensor&sprefix=current+sensor%2Caps%2C382

Here's one that is good for up to 30 A that will only run you $7:
http://www.amazon.com/Current-SCT-013-030-Non-invasive-Split-Core-Transformer/dp/B00L51AD3W/

One good for 120 A for $12:
http://www.amazon.com/0-01-120A-0-5M-Split-core-Current-Transformer/dp/B005FIFT4E/

and it looks like there may be some interface boards designed to glue
these to an Arduino or something, but all you should need is an A-to-D.
(See user reviews on the last one for some tips on attaching it to an
Arduino.)

These are all "split-core" probes - meaning the coil opens to be placed
over a wire. For your branch circuits, you might be able to save by
using coils that don't open, like:

http://www.amazon.com/Leviton-CDA02-L12-Sub-Metering-Current-Transformer/dp/B0055D6F92/

One of the Amazon Merchants is selling that particular one for $10,
which isn't really a bargain, but I bet similar coils could be found for
under $5. The savings trades off for higher installation effort, as
you'll have to remove the wire to each breaker to install it.


Another option to investigate is whether you can get a breaker with
integrated sensors. Such a thing might not exist for residential
applications. But if it did, you'd end up with a much cleaner
installation. (Some modern circuit breaker designs use current sensing
electronics instead of the old style thermo-magnetic design. So a lot of
the hardware you'd need is already in the breaker.)

At one time SquareD (now Schneider Electric) had a line of breakers that
fit their QO family of panels (stay away from the lower-end Homeline
panels) that facilitated remote switching of the breaker. I don't recall
what sensor information it provided. I don't spot anything like that on
their breaker page now:

http://www.schneider-electric.com/products/us/en/50300-circuit-breakers/

And they do have a remotely operated breaker made for lighting panels:
http://www2.schneider-electric.com/resources/sites/SCHNEIDER_ELECTRIC/content/live/FAQS/228000/FA228072/en_US/1210CT0201.pdf

but it's a pretty old-school design using a motor to mechanically move
the breaker, and no sensors.

The breaker replacement approach, even if you can find then, is unlikely
to be cheaper. You'd probably have to start by replacing the whole panel
 and the material costs would likely be twice what regular breakers
would run. ($1000 for a typical panel replacement parts and labor, so
$2000+)

 -Tom