I have read and researched online about electric monitoring systems like the kill a watt and wattspn and i have observed something in vpmmon, they do reuire intrusive devices like sockets as means of controlling (on or off the devices) and monitoring mechanism. Now is there a diffent way or idea in order to control and monitor electric appliances in a non intrusive way (without using additional sockets to be placed on each load)? I know non intrusive mechanism can do monitor stuff like what is on or off through voltage variations, but it cant control the loads like turning them on or off. Thanks

  • \$\begingroup\$ Kindly add proper tags if possible, tnx \$\endgroup\$ Mar 27, 2012 at 9:47

2 Answers 2


On/off control is, by definition, intrusive. ie
The act of turning something off IS intrusive.
The act of turning something on IS intrusive.


You can measure AC current without intrusion and
You can measure AC voltage with very close to zero intrusion.

While it IS possible to monitor voltage without intrusion in the strict sense
ie with no ohmic connection, by using eg capacitive coupling,
there are few circumstances where this makes practical sense.
Even DC voltage may be measured using electrostatic methods but this would essentially never be done in AC mains measurements.
Long long ago I did see and electrostatic DC meter ! Rare.

Ac current can be measured by detecting the field produced - most usually with a Hall sensor.
Special ICs are made for this purpose.

Clamp meters of the sort shown by Rocketmagnet in his answer are also useful.

Here is an AC current sensor which uses a Hall sensor.
The current path is built into the IC for precision but this is not essential.
There is no "ohmic" contact with the current path.

enter image description here

  • \$\begingroup\$ is it possible to control your electric appliance through means of a non intrusive way (not putting sensors / additional sockets and wireless transmistters and stuff) \$\endgroup\$ Apr 1, 2012 at 7:49
  • \$\begingroup\$ @user963499 - covered in the 1st 6 lines of my existing answer. Explained further in the following text. If you want more detail you need to explain what you are trying to achieve in more detail. \$\endgroup\$
    – Russell McMahon
    Apr 1, 2012 at 10:12
  • \$\begingroup\$ I was thinking to create a centralized electrIc appliance control and monitoring system like the "kill-a-watt" ,wattson,etc, but they all use additional sockets to turn On/off the load through a wireless trsnsmtter. And now, ive research that there is other way around to monitor the load by putting a sensor in the main wire of your house beside the electric meter and what it does is sense the voltage variations and do some complex math ( since every load has something like its own signature )so in turn it can distinguish one from the other \$\endgroup\$ Apr 1, 2012 at 23:09
  • \$\begingroup\$ Yet non intrusive technique is like a 1- way in which you cannot send instructions/info/signals or even cut the current thriugh that will route since it would need modifications in each of the power outlet/socket of your house to be effective \$\endgroup\$ Apr 1, 2012 at 23:13

While it is possible to measure load current in a non-intrusive way, using a clamp ammeter like this:

Clamp Ammeter

It is not really possible to control the current in the cable. Certainly not possible to switch appliances on and off.


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