What is a Class B circuit?

• A. Circuit not capable of transmitting an alarm beyond the location of a single open or non-simultaneous single ground fault
• B. Circuit not capable of transmitting an alarm beyond the location of any fault at all
• C. Circuit capable of transmitting an alarm during a single open fault
• D. Circuit transmits an alarm only when the power is off

Answer: (A)

A Class B circuit is a single-path signaling arrangement where alarms must travel along one direct path to the control panel. If a single fault occurs on that path—such as an open circuit or a ground fault that isn’t occurring at the same time in two places—the signal cannot be transmitted beyond the fault. In practical terms, alarms from devices located past the fault won’t reach the panel, so the system loses those downstream signals. This characterizes Class B as less fault-tolerant than Class A, which provides alternate routing so signals can still get through if a fault occurs.

The description you’re looking for matches this behavior: an alarm cannot be transmitted beyond the location of a single open or non-simultaneous single ground fault. The other statements describe conditions that don’t align with how Class B circuits operate—for example, signaling continuing during a fault, or requiring power to be off, or claiming alarms aren’t transmitted beyond any fault at all.