SparkFun Forums 

Where electronics enthusiasts find answers.

General project discussion / help
Did you make a robotic coffee pot which implements HTCPCP and decafs unauthorized users? Show it off here!
By mehdoodle
After spending 4 hours googling I have a lot of good info but not enough unfortunately. Hoping one or more electrical wizards can help me fill in the gaps.

The use case: I have a generator hooked up to the house (yes it's done safely, let's not get into that) but no good way to know when the utility power comes back on, short of walking down the driveway to look at a street lamp. I want to create a simple current monitor that can send an event to IFTTT when it sees current on the line. Important point there - not looking to measure current, just wanting to know when there is current at all on the utility feed.

Obstacles: Not an electrician, need to keep it economical

The tentative solution:
-Arduino or Pi (etc) with wifi
-Current sensor such as this ( ... sensor-ct/)
-Clamp the current sensor on the utility feed before the electrical panel. (Non-invasive split core current transformer, so I'm not doing any electrical work)
-While utility power is good, the sensor senses whatever current exists and is good. While utility power is down, the sensor doesn't sense anything and the Arduino/Pi alerts based on that lack of voltage.

I am pretty good at brute force working on something until I figure it out, however when we're talking about electricity I am not into trial and error. This is the most relevant article I have found ( ... th-arduino) but once it starts getting into current and resistance calculations I am in over my head.

Specific Questions:
-Does the clamp sensor just sense the magnetic field in the line, or does it actually pick up and transmit current while clamped around the line?
-If it transmits current, how would a layperson be sure that all the numbers are correct? Since this isn't intended to measure current, how would one ensure that this sensor contraption is built to accommodate the highest voltage that could be present on the feed?

Hopefully that's not too incoherent, thanks in advance!

PS - If the answer is ultimately that I can't be sure I won't cook myself without hiring someone, that's fine but disappointing. :)
By lyndon
If your transfer switch is turned to the house, how are you going to sense current on the utility side? You can get a voltage reading, but there should be no current flow unless you wire something on that side of the line.

Who is your power company? You may be able to find a public API to their web service so this could all be done in software.
By n1ist
Have an electrician install an outlet on the utility side of the transfer switch (you may need a separate fuse for it). Then plug in a wall wart and connect its output to the I/O pin on the arduino thru an optoisolator or divider. If the wallwart is on, utility power is on.
By jremington
If you have a house circuit that is NOT bypassed by your generator transfer switch, monitor that line using a noninvasive current transformer at the breaker box, or a wall wart as mentioned above.

A CT won't detect a power up situation if no current flows, so there must be an active load on the line being monitored.