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NOTE: This is an unformatted excerpt from our online fire protection training library.

NEC Requirements

Power-Limited

Definition

A power-limited fire alarm circuit is one, which is powered by a source that is inherently limited in the amount of current that can be on the circuit, even under fault conditions. The limit for direct current voltages of 20 to 100 is 100 volt-amperes This is why most fire alarm circuits are designed to operate at a maximum of 24 volts DC with a maximum current flow of 4 amperes. (24 volts x 4 amperes = 96 volt-amperes, which is less than the 100 VA threshold set for power-limited circuits.. In general, the physical wiring installation requirements for power-limited circuits are less restrictive than for non-power-limited circuits. However, the installation requirements regarding the combining of different circuits in the same cable, conduit, or raceway are more restrictive for power-limited circuits than they are for non-power-limited circuits.
NOTE: This is an unformatted excerpt from our online fire protection training library.

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