in series

In series means electrical components are connected in a single chain, with current flowing through one component and then the next in sequence. The positive terminal of one device connects to the negative terminal of the next. Current has only one path to follow, so the same amperage passes through every component in the chain.

The voltage drops across each component as current passes through it. If you connect three 12V batteries in series, you get 36V across the terminals, but the amperage is limited by the weakest link. Resistances add together: 10 ohms plus 20 ohms in series gives 30 ohms total. This makes series configurations useful for stepping up voltage or limiting current flow through sensitive equipment.

Series versus parallel

Series and parallel are opposite topologies. In parallel, components share the same voltage across them, but current divides between paths. Household electrical outlets are wired in parallel so each device gets the same voltage independently. Series circuits are common in battery strings, lighting chains, and load protection circuits where you need cumulative voltage or controlled current restriction.

The critical drawback of series is failure dependency: if one component breaks or disconnects, the entire circuit opens and nothing works. A broken light bulb in old Christmas light strings in series would kill the whole strand. Modern decorative lights use parallel circuits for this reason. Industrial control systems often use series circuits deliberately when this failure mode is acceptable or desired, such as in safety interlocks where breaking the circuit is the safe state.

Series connections appear in rectifier stacks, where diodes are stacked in series to handle high voltages. In power distribution, series impedance is sometimes added intentionally to limit fault current. The term is fundamental: you cannot speak accurately about circuit design, troubleshooting, or electrical safety without it.