class 1,2, and 3 circuits

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cartman

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Could someone please give me an example of what a class 1,2, and 3 circuit would be? For example is the thermostat wire I have in my house considered class 2? Thanks
 
Re: class 1,2, and 3 circuits

cartman,- IMO Art 725 is one of the most difficult in NEC to get a full grasp on. It is one of the articles that I am least comfortable with. Thus, do not trust me 100% on this.
Here are some greatly simplified common examples, there are many others.

Class 1: 120V. control ckt. for a lighting contactor. Has fire/shock hazards like most of our electrical "stuff" & uses NEC Chapter 3 wiring methods.

Class 2: 12,16,18,24V. for doorbell or for central air thermostat in a dwelling. Use listed Class 2 xfmr power source. No shock/fire hazard.

Class 3: 70V. public address speaker system in large industrial building. Use listed Class 3 xfmr power source. Shock hazard but no fire hazard.

Notice that motor control ckts. are not mentioned. They are covered in the very-well-written Article 430.
 
Re: class 1,2, and 3 circuits

kiloamp7,
In my opinion the rules in both 430 and 725 apply to motor control circuits.
Don
 
Re: class 1,2, and 3 circuits

Does the Code really talk about the fire/shock hazards of thess classes of circuits?

[ January 02, 2005, 10:04 PM: Message edited by: midget ]
 
Re: class 1,2, and 3 circuits

Art 725, under class 1 circuit applies to motor control circuit with overcurrent protection such as a external control voltage source.
Art 430 Part XI applies to a control circuit that is tapped from a motor branch circuit.
 
Re: class 1,2, and 3 circuits

Yes, a greatly simplified explanation does not include how Art.430 covers a motor control ckt. that is tapped from the motor branch ckt. or how Art.725 would cover a motor control ckt. say, 120V. separate control source from a remote panelboard.

tom baker is correct on that.

midget - NEC is not an instruction manual, but 725.2 does acknowledge the fire/shock hazard thing for Class 2 & 3.
 
Re: class 1,2, and 3 circuits

Did some research on this article one time [Art 725] and came to the following conculsion...

Cl-I P/L [Power Limited] 30vmax @1000va

Cl-I NPL [Nonpower limited] 120v and up

Cl-II 31-119 volts

Cl-III Wet Location for a class II circuit..

Least that how I use the information...
 
Re: class 1,2, and 3 circuits

In reply to Midget....
There is No Hazard for equipt. operating at 50 volts or less ac or dc....in accordance with NFPA 70-E
 
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