Basic Circuit Design
Continuing Education Units (CEU): 0.10
Expected Duration: 1 Hour
This self-paced online course covers the basic concepts of wiring schemes for fire alarm systems. Wireless systems are not discussed, as they represent only a small percentage of fire alarm system installations. The fire alarm circuit wiring serves as a key factor in the ability of a fire alarm system to work correctly.
Upon completion you should be able to:
- Explain the difference between "power limited" and "non-power limited" categories of system wiring
- List the three basic types of fire alarm circuits: initiating device circuits, notification appliance circuits, and signaling line circuits
- Understand that these circuits can be wired as Class A or B, depending upon the system objectives and recommendations from the authority having jurisdiction
- Discuss supervision and monitoring, as a function of how the system is wired and the components that are used
- Explain when and why T-tapping can be allowed
Who Will Benefit
Anyone whose job involves designing, reviewing, evaluating or installing fire protection systems, including: designers, installers, engineers, electrical contractors, technicians, project managers, fire marshals, and architects.
- The fire alarm circuit wiring serves as a key factor in the ability of a fire alarm system to work correctly. If wired improperly, there is no guarantee that the signals will be properly transmitted.
- The two general categories of system wiring are "power-limited" and "non-power-limited":Â
- power-limited fire alarm systems receive their power from power supplies to limit the voltage and current to safer levels
- non-power-limited systems receive power from power supplies that have higher power levels
- In any case, the National Electrical Code forbids fire alarm systems to operate at more than 600 volts.
- There are three basic types of fire alarm circuits.
- initiating device circuits put information into the system
- notification appliance circuits distribute information from the system
- signaling line circuits may either put information into the system or distribute information from the system
- Initiating devices are also known as "conventional," whereas signaling line circuits are known as "addressable" or "intelligent."
- These circuits can be wired as Class A or B, depending upon the system objectives and recommendations from the authority having jurisdiction.
- Class A circuits cannot lose their ability to transmit a signal if there is a single fault in the circuit. Devices or appliances connected to a Class B circuit, however, can be impaired beyond a broken wire in the circuit.
- Regardless, all fire alarm circuits must be monitored for integrity so that any fault in the wiring or any component is indicated at the control unit as a trouble signal. This supervision or monitoring for integrity is a function of how the system is wired and the components that are used.
- Fire alarm systems can also have building fire safety circuits that will turn on or turn off equipment to make a building safer in a fire emergency. An example would be elevator recall, which is routinely done by interfacing the elevator controls with the fire alarm system.Â
- Signaling line and initiating device circuits may both serve as input circuits, but operate quite differently:
- signaling line circuits are considered intelligent because they can identify individual components that have initiated a signal
- initiating device circuits cannot do this, but instead merely identify that one of the devices on the circuit has operated, without identifying which one
- Either circuit type can be used at the discretion of the owner, designer and/or the authority having jurisdiction.
- T-tapping is a way to add components to the system without breaking into the circuit's wires. Because a T-tapped component can compromise the monitoring for integrity of a Class B initiating device circuit, the only circuit that can be T-tapped is a Class B signaling line circuit. Because a T-tapped portion of a circuit will compromise the ability of a connected component to remain in service under a fault condition, Class A circuits, no matter which type, must never be T-tapped.