A single-pole general-use switch is being installed on a 120-volt branch circuit that has one ungrounded conductor and one grounded conductor. How does the Code treat the grounded conductor at that switch?
- The switch shall open the ungrounded conductor, unless the switching device opens all conductors of the circuit at the same time
- BThe switch may open either conductor of the circuit, whichever makes the wiring in the box simpler to arrange
Leaving the choice to the installer is exactly what this rule prevents. Opening only the grounded conductor leaves the load and everything downstream of the switch sitting at line potential.
- CThe switch shall open the grounded conductor, so that the load is isolated from earth and cannot leak current to ground when the switch is off
This inverts the rule. Isolating the load from the grounded conductor leaves line voltage on the equipment, which is the hazard a person servicing a luminaire walks into with the switch off.
- DThe switch may open the grounded conductor wherever the circuit also has ground-fault circuit-interrupter protection
Ground-fault protection responds to current leaving the circuit. It does nothing about a load that is still connected to the ungrounded conductor after the switch has been opened.
Why A is correct
The requirement is that switching take place in the ungrounded conductor so that opening the switch actually de-energizes the load. A device that opens every circuit conductor at the same moment is acceptable because there is no interval during which the load sits energized through an unswitched ungrounded conductor.
What this question is testing
This checks a foundational safety rule and the way the Code writes its narrow allowance for multipole devices. Candidates who read the allowance as a general permission to switch the grounded conductor pick the wrong answer.
On the job
Older two-wire switch loops and hurried remodels produce switched neutrals more often than anyone likes to admit, and the symptom is a lighting circuit that reads zero volts across the lamp but 120 volts from the shell to a ground rod. Somebody eventually finds it with a knuckle. When a service call reports a tingle from a light fixture that is switched off, a switched grounded conductor is near the top of the list, right alongside a broken grounded conductor upstream.
Memory technique
Switch the hot; the white stays put.
Exam tip
Read the phrase all conductors simultaneously carefully. That is the only door the Code opens for switching a grounded conductor.
Where to look it up
Article 404, the opening sections on switch connections, covering three-way and four-way switching and grounded conductors.