Electronic – Can single clamp measure total current from 3 wires


Single AC clamp can measure current flowing through a single wire in a non-invasive way. There are AVR/Arduino projects use such a clamp to measure house power usage. However, they use 3 clamps for 3 main wires that come into house breaker box. Unfortunately, I don't have access to separate wires in my breaker box. I can only access main power cable that comes to my house through the roof, and that cable has all the wires inside itself (is this a good assumption?) without possibility to separate them. If that is so, then the question is can I use a single clamp on that main cable for my own little power usage measurement AVR project, and if I can then is there some reason for it to be less reliable then 3 clamps solution?

Best Answer

No, you cannot use a clamp meter on both the live and neutral wires at the same time. Current flowing back through the neutral wire will effectively cancel out current flowing through the live wire, and it will read 0 amps (assuming no current is leaking out anywhere).

One clamp around the live wire should give you the reading you want.

I don't know why you would need 3 clamps though, unless you have 3 phase coming into your building, in which case you'll need to sum the 3 separate currents to get the total current used.