Class 2 power supplies

[jonesy29847]

Where are class two power supplies required? More specifically if an industrial control circuit (24VDC) is powered by a supply limited to <8A?

Does an industrial control circuit fall under the classification a remote-control and signaling circuit?

Thanks for your help.

 

[waross]

NEC 725-2. (1996)
Class 2 Circuit:........."a Class 2 circuit considers safety from a fire initiation standpoint and provides acceptable protection from electric shock."
See NEC Article 725

 

[jonesy29847]

waross, you need to get a more recent version of NEC, thanks for your help.

From NEC 2005:
725.1 This article covers remote-control, signaling, and power-limited circuits that are not an integral part of a device or appliance.

The difficulty I am having is determining if an industrial control circuit is within the scope of 725. Is it a device?

Further in the General Discussion section, I find the following:
Class 1 remote-control circuits are commonly used to operate motor controllers in conjunction with moving equipment or mechanical processes, elevators, conveyors, and other such equipment. Class 1 remote-control circuits may also be used as shunt trip circuits for circuit breakers. Class 1 signaling circuits often operate at 120 volts but are not limited to this value.

None of the circuits I am considering have motor controlers, nor conveyors, however is an assembly system considered a mechanical process?

As you can see the matter is quite confusing and in deciding that compliance with class 2 is required we will have to double power supplies in the assembly system.

 

[waross]

jonesy29847
Your right about the code, but I'm a long way from home. My Canadian code is a little newer but it's too old also. One thing it does is define Class 1 and Class 2 a little better.
I don't know if it will help you, but as I read the Canadian Code; You choose the power supply to suit the application and then check the code for the applicable wiring methods.
You can use smaller wire for class two.
You must keep Class 2 wiring separate from other wiring but you can run Class 1 with power conductors if their going to the same machine.

To say it another way, select a power supply that will do the job. Then depending on whether it's Class 1 or Class 2, install, protect and wire it accordingly.

 

[tommom]

Class 2 circuits are allowed by NEC to allow the use of for example, plenum-rated wire in lieu of conduit/wire, or other wiring method as described in Chapter 3, and allows a lower insulation rating for the cable used (typically 300 volts, instead of 600 volts for building wiring.)

 

[resqcapt19]

Industrial controls are covered by Article 725. You are never requried to use a Class 2 system. There are just some advantages in the required wiring methods if you do. Note that to use these advantages, the power supply must be a listed Class 2 power supply. I have never seen a listed class 2 power supply in industrial equiment. If the power supply is not listed, then it is a Class 1 system and you must follow those rules.
Don