What it means
Most electrical devices that control or protect a circuit — breakers, disconnect switches, fuses, meters and GFCI outlets — have two sets of connections. The line side connects to the incoming supply: the utility, a transformer or an upstream panel. The load side connects to whatever the device feeds downstream: a branch circuit, a motor, a panel or other outlets.
The terms are relative. The load side of a main breaker becomes the line side of the next panel it feeds, so every point in a system has something upstream and something downstream.
An example: in a disconnect switch serving an HVAC unit, the incoming feeder lands on the line terminals and the conductors to the unit leave from the load terminals. Opening the switch de-energizes the load side — but the line side stays energized, because it’s still connected to the supply.
Why it matters
- Safety. Turning off a breaker or opening a disconnect does not de-energize its line side. Line-side terminals should be treated as energized until verified otherwise.
- Correct wiring. Devices such as GFCI outlets are marked LINE and LOAD. Reversing the connections can leave downstream outlets without the protection they’re meant to have.
- Clear communication. Electricians, engineers and inspectors use “line side” and “load side” to say exactly which side of a device they mean.