NFPA 731 Photoelectric Detectors.

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The photoelectric detector uses a light transmitter and a photoelectric receiver and will trigger when the beam of light has been interrupted or crossed.

Photoelectric detector units must comply with applicable standards, such as ANSI/UL 639, Standard for Safety for Intrusion-Detection Units.

According to UL 639, Section 66.1.2, “The beam shall not be visible in a darkened room nor in a dusty or smoky atmosphere.

66.1.3 The light source shall not be visible when viewed at an angle of 15 degrees or more from the axis of the beam.”

Below is a sample of NFPA 731. For the complete section, see the actual NFPA 731 text at NFPA.ORG. Once there, click on the free access link to the latest edition of NFPA 731.

5.3.3.1.8 Photoelectric Detectors. Photoelectric detector units shall be in compliance with applicable standards, such as ANSI/UL 639, Standard for Safety for Intrusion-Detection Units.

NFPA 731 Photoelectric Detectors.

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Which of the following is true regarding photoelectric detectors?

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	A:	The beam shall be visible in a darkened, smoky room or similar atmosphere.
	B:	The light source shall not be visible when viewed at an angle of 15 degrees or more from the axis of the beam.
	C:	The light source shall be visible when viewed at an angle of 25 degrees from the center of the beam.
	D:	The transmitter shall be visible in a darkened, smoky room or similar atmosphere.

NFPA 731 Photoelectric Detectors.

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NFPA 731 Photoelectric Detectors.