class rating of cat5 FREE cabling and networking Helpdesk
 Question by Don Georger posted 30 Jan 2001
 class rating of cat5
What is the difference of cat5 e class 2 and cat5 e class 3 and what dose cm stand for
 Answer by Roman Kitaev posted 30 Jan 2001
Hi, Don!

Class 2 and Class 3 definitions are covered in the NEC (National Electrical Code) Article 725 "Class 1, Class 2 and Class 3 Remote-Control, Signaling, and Power-Limited Circuits".

Class 2 Circuit is "Wiring System between the load side of a power source and the equipment. This circuit is power-limited, is considered safe from fire initiation, and provides protection from electric shock".

In Class 2 circuits, Class 2 cables are used.

Class 3 Circuit is "same as Class 2 circuit, with higher voltages permitted. ".

In Class 3 circuits, Class 3 cables are used.

"CM" is a listing requirement also from the NEC (Article 800-51) and stands for "Communications General Purpose". CM cables may not be used in plenum and riser spaces.

Hope it helps,

Roman Kitaev, RCDD

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