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Is it possible to be able to measure a single 15A circuit at any point along the circuit to determine if there is a current draw on that circuit and how much it is?

I'd like to figure out how to put a sensor on my home's circuits to be able to integrate the results into my home automation system, and thus, be able to create limits that would trigger specific scripts or routines, etc.

  • What sort of analog sensor inputs can your home automation system take? Also, where do you want to put the sensors? – ThreePhaseEel Apr 16 '18 at 1:15
  • With my home automation system, all loads are controlled and the system knows the status of each. As such, I don’t have the need to sense most loads—because the status is already known. The single load that is sensed is the sump pump to determine if it might not be working (i.e. rain totals without run-time or 100% run-time). – Tyson Apr 16 '18 at 1:52
  • Inputs are limited to my imagination through either a Raspberry Pi or Arduino. – Jon Griffith Apr 16 '18 at 1:54
  • @JonGriffith -- have you worked with 4-20mA current loops at all before? – ThreePhaseEel Apr 16 '18 at 3:39
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There are a variety of pre-made products which do just that. The controller sits inside your electrical service panel (or on a single circuit) and you place a "clamp meter" around the hot wire in question. It then communicates with you via powerline signaling or WiFi (cute little WiFi antenna pokes out of a knockout on your service panel.

Obligatory warning that nothing about being an electronics guy prepares you for the requirements of mains electrical (and in fact mis-trains you). One cannot just hack random electronic components into a mains electrical system, even if the components are UL listed. You may only use approved, preassembled equipment that has been UL* listed as equipment for use with mains power, and you must install it according to its labeling and instructions**. These items are not found at Mouser electronics, Amazon Marketplace, and damn well not Alibaba. They are found at big-box retailers (though they can be sloppy) and your local electrical supply house. You also cannot mix class 1 and low voltage wiring.


* or similar testing lab. CE is not a testing lab.

** because the listing is contingent on installation in that manner.

  • Or even simply a wired connection (although the category I'm talking about is more for inside an industrial control panel) – ThreePhaseEel Apr 16 '18 at 22:41
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Yes. Measuring the current is another problem.

I just bought one of these and it works good. It is a current relay. Several companies make them in different packages and current ratings. This will give you an on/off feedback at a minimum turn-on current.

Now, measuring how much current is another problem that will require an analog input to your home automation system and an analog sensor that will have a proportional output to the current measured.

This would involve a current transformer that has a voltage output and scaled to fit the input to your system. E.g. 1-5 volts, 0-10 volts, etc.

Good luck!

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