NCCR Electrical Practice Test

To measure current, an ammeter must be placed in series with the circuit so that all the current in that path flows through the meter. Current is the same through every component in a single loop, so putting the meter in line ensures it reads the actual current in that branch. If you connect an ammeter in parallel—across a component or the supply—the meter provides an alternate path of very low resistance. That can shunt current away from the load, distort the circuit, or even cause a short, giving an incorrect reading or damaging the circuit. Placing the meter in series keeps the current path intact and lets the meter measure the true current flowing through the circuit.