Blondel's theorem, named after its discoverer, French electrical engineer André Blondel

André Blondel

André-Eugène Blondel was a French engineer and physicist. He is the inventor of the electromechanical oscillograph and a system of photometric units of measurement.-Life:...

, states that, in a system of N electrical conductor

Electrical conductor

In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...

s, N-1 electrical meter or wattmeter

Wattmeter

The wattmeter is an instrument for measuring the electric power in watts of any given circuit.An instrument which measures electrical energy in watt hours is essentially a wattmeter which accumulates or averages readings; many such instruments measure and can display many parameters and can be...

 elements, when properly connected, will measure the electrical power

Electric power

Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...

or energy taken. The connection must be such that all potential coils have a common tie to the conductor in which there is no current coil. For example, a 3 phase 3 wire system needs only two watt meters, but a 3 phase 4 wire system (with a neutral) needs three. The theorem is based on a paper delivered by Blondel in 1893 at the
International Electric Congress in Chicago.