Class 1, Class 2, or Class 3 Circuits

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ChuckB

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I hope there is somebody out there that can set me straight.

We are currently working at an airport installing an automatic people mover system and have run into an issue. We have installed a metal trough under a station platform for installing our cables. We purposely purchased a Tray rated cable with 600v insulation for all of our circuits (highest voltage is 120v), including any communication type cable thinking that it was ok to run all of this together in the tray without the use of a divider. The clients code department has since come back to us telling us that we can not install power, control, Class 1 circuits, and communication circuits together without dividing them. Is there anything in the NEC that supports this or am I stuck with a divider. Also, what makes a circuit a class 1 circuit. I was under the impression that there were just normal power, lighting, control, and signal circuits and then there was this classification for other circuits (Class1, Class2, or Class 3).
 
Take a look at 725.2 and 725.55(H)

Class 1 Circuit. The portion of the wiring system between the load side of the overcurrent device or power-limited supply and the connected equipment. The voltage and power limitations of the source are in accordance with 725.21.
Class 2 Circuit. The portion of the wiring system between the load side of a Class 2 power source and the connected equipment. Due to its power limitations, a Class 2 circuit considers safety from a fire initiation standpoint and provides acceptable protection from electric shock.
Class 3 Circuit. The portion of the wiring system between the load side of a Class 3 power source and the connected equipment. Due to its power limitations, a Class 3 circuit considers safety from a fire initiation standpoint. Since higher levels of voltage and current than for Class 2 are permitted, additional safeguards are specified to provide protection from an electric shock hazard that could be encountered.
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(H) Cable Trays. Class 2 and Class 3 circuit conductors shall be permitted to be installed in cable trays, where the conductors of the electric light, Class 1, and non?power-limited fire alarm circuits are separated by a solid fixed barrier of a material compatible with the cable tray or where the Class 2 or Class 3 circuits are installed in Type MC cable.
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If your installing only cables and not individual power conductors why is there a problem?
 
infinity said:
If your installing only cables and not individual power conductors why is there a problem?
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The clients code depratment stated that it does not matter as to what type of cable we used that everything is still based on the type of circuit.
 
Chuck. as infinity pointed out, the key is separation is required between conductors, think single conductor tray cable. Multi conductor tray cable is an Art 300 wiring method, no separation is required. A class 1 circuit is wired with a chapter three wiring method, but class 2 and 3 can be CL2 or CL3 cables.
You could always run the power lighting and class 1 in MC cable, clearly no separation is required to an MC cable. But use the same logic with tray cable.

The requirements for Class 1 2 3 are in Art 725. If you PM me I have a simple chart that lays out the differences I can email to you.
 
Class 1, Class 2, and Class 3 circuits are differentiated from each other by power limitations. Section 725-2 provides definitions of Class 1, 2 and 3 circuits. Class 1 circuits may or may not be supplied by power-limited sources. Class 2 circuits are limited to voltage and current values that will not usually present a shock or fire hazard. Class 3 circuits are allowed to have higher of voltage and current than Class 2 circuits. The voltage and current levels of Class 3 circuits may present a shock hazard but generally do not present a fire hazard.
 
These articles refer to conductors. A listed cable such as MC or TC provides the necessary separation. As long as you are using tray cable for the Class 1 and power/lighting circuits you could use a CL2 or CL3 cable in the same tray without a divider for the communications and control.

Class 1 is not the same as power and lighting though they both have to be installed per Chapter 3 wiring methods. Generally, a Class 1 circuit is supplied from a separately derived source such as a transformer secondary, battery, power supply or the output of an audio amplifier.

-Hal
 
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