Class 1, Class 2 circuits.

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Dsg319

Senior Member
Location
West Virginia
Occupation
(Green)Master Electrician
I have some sump pumps I am currently working on at a project. And plan to leave the motor starter in a common raceway with my branch circuit conductors supplying the motor, and also the 120volt control circuit conductors with OCPD, which will go to a float/switch.

From what I gather that is okay. Am I right in calling those control conductors a class1 signaling circuit?
 

Dsg319

Senior Member
Location
West Virginia
Occupation
(Green)Master Electrician
I’m not good at classifying really. If someone could explain class1,class2, and class3 in laymen terms that would be great.

From what I understand obvious doorbells and such is a class 2 circuit.

But what about an analog/digital input or output circuit from a PLC. Is that class 2 as well? Am I correct in saying those could not share the common raceway with AC power conductors.
 

DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
Class 2 is a power limited supply, which means there is not enough juice to start a fire in a short circuit condition. You can actually dead short a class 2 power supply and nothing will happen. Probably will shorten it's life though. All class 2 power supplies list their maximum short circuit current to determine wire sizing.

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don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Class 2 is a power limited supply, which means there is not enough juice to start a fire in a short circuit condition. You can actually dead short a class 2 power supply and nothing will happen. Probably will shorten it's life though. All class 2 power supplies list their maximum short circuit current to determine wire sizing.

Sent from my BE2028 using Tapatalk
Some transformers with a Class 2 output have an internal fuse under the outer wrapping over the winding...so a short opens the fuse and you pretty much throw the transformer away. However it is possible to remove the wrapping and solder a new fuse in :)
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Class 2 is defined by the power supply.
PLC ckts are typically class 2 and can’t share a raceway with lighting and power conductors
I wouldn't say typical. Most DC circuits and analog circuits probably qualify as class two but 120 volt AC circuits are almost certainly class one. Some PLCs have really output second maybe get you into a power circuit.
 

Dsg319

Senior Member
Location
West Virginia
Occupation
(Green)Master Electrician
What about a 5amp 24vdc circuit that powers a device. Would it be class 1?

I often see that in the same cable/raceway with class 2 PLC input circuits.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
Dsg, Tom answered your question, but to make it clear and in layman's terms, it isn't up to you or me to "classify" class 2 wiring. The power supply must be labelled as a Class 2 power supply in order to install its wiring in a class 2 manner.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Dsg, Tom answered your question, but to make it clear and in layman's terms, it isn't up to you or me to "classify" class 2 wiring. The power supply must be labelled as a Class 2 power supply in order to install its wiring in a class 2 manner.
Sort of. If a listed item has power characteristics in the range of a class 2 ckt it is a class 2 ckt. Like Ethernet
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Sort of. If a listed item has power characteristics in the range of a class 2 ckt it is a class 2 ckt. Like Ethernet

We've had hot debates over Ethernet being CL2. The NEC, in it's infinite wisdom, seems to think it is and so it is included in Art 725. Ethernet carries no power and is a communications circuit. There are no labels on equipment data ports calling for CL2 wiring as would be required. So where does that come from? I think it was because Ethernet came along after 725 and 800 were written and they just stuck it in 725 because they didn't want to rewrite anything.

Unless of course the Ethernet cable carries power for POE which would make it CL2. But Ethernet was under 725 long before POE.

-Hal
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
We've had hot debates over Ethernet being CL2. The NEC, in it's infinite wisdom, seems to think it is and so it is included in Art 725. Ethernet carries no power and is a communications circuit. There are no labels on equipment data ports calling for CL2 wiring as would be required. So where does that come from? I think it was because Ethernet came along after 725 and 800 were written and they just stuck it in 725 because they didn't want to rewrite anything.

Unless of course the Ethernet cable carries power for POE which would make it CL2. But Ethernet was under 725 long before POE.

-Hal
Emergency in the code that there has to be a marking saying that it's class 2? You should read article 725 very closely. I think you will find that it doesn't actually say that.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
My understanding is that if a power source is not labeled either CL2 or CL3 (no label) you have to assume Class 1 and wire using a Chapter 3 wiring method.

-Hal
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Read what article 725 says about it
You mean this part?
(A) Power Source.

The power source for a Class 2 or a Class 3 circuit shall be as follows:
  • (1) A listed Class 2 or Class 3 transformer
  • (2) A listed Class 2 or Class 3 power supply
  • (3) Other listed equipment marked to identify the Class 2 or Class 3 power source
Or this part?
725.130 Wiring Methods and Materials on Load Side of the Class 2 or Class 3 Power Source.
Class 2 and Class 3 circuits on the load side of the power source shall be permitted to be installed using wiring methods and materials in accordance with either 725.130(A) or (B).

If the circuit is not supplied by a Class 2 o3 3 power supply, you can't use Class 2 or 3 wiring methods. If you can't use Class 2 or 3 wiring methods, you are left using Class 1 wiring methods.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
(A) Power Source.

The power source for a Class 2 or a Class 3 circuit shall be as follows:
  • (1) A listed Class 2 or Class 3 transformer
  • (2) A listed Class 2 or Class 3 power supply
  • (3) Other listed equipment marked to identify the Class 2 or Class 3 power source
I was with you, but he is right, per the above note 1 the power supply must be listed as class 2 but is not required to be labeled as class 2.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
725.121 Power Sources for Class 2 and Class 3 Circuits.
(A) Power Source. The power source for a Class 2 or a Class 3
circuit shall be as specified in 725.121(A)(1), (A)(2), (A)(3),
(A)(4), or (A)(5):
Informational Note No. 1: Informational Note Figure 725.121,
No. 1 illustrates the relationships between Class 2 or Class 3
power sources, their supply, and the Class 2 or Class 3 circuits.
Informational Note No. 2: Table 11(A) and Table 11(B) in
Chapter 9 provide the requirements for listed Class 2 and
Class 3 power sources.
(1) A listed Class 2 or Class 3 transformer
(2) A listed Class 2 or Class 3 power supply
(3) Other listed equipment marked to identify the Class 2 or
Class 3 power source
Exception No. 1 to (3): Thermocouples shall not require listing as a
Class 2 power source.
Exception No. 2 to (3): Limited power circuits of listed equipment where
these circuits have energy levels rated at or below the limits established
in Chapter 9, Table 11(A) and Table 11(B).

Informational Note: Examples of other listed equipment are as
follows:
(1) A circuit card listed for use as a Class 2 or Class 3 power
source where used as part of a listed assembly
(2) A current-limiting impedance, listed for the purpose, or
part of a listed product, used in conjunction with a non–
power-limited transformer or a stored energy source, for
example, storage battery, to limit the output current
(3) A thermocouple
(4) Limited voltage/current or limited impedance secondary
communications circuits of listed industrial control equipment
(4) Listed audio/video information technology (computer),
communications, and industrial equipment limited-power
circuits.
Informational Note: One way to determine applicable
requirements for listing of information technology
(computer) equipment is to refer to UL 60950-1-2011,
Standard for Safety of Information Technology Equipment.
Another way to determine applicable requirements for
listing of audio/video, information and communication
technology equipment is to refer to UL 62368-1-2014,
Safety of audio/video, information and communication technology
equipment. Typically such circuits are used to interconnect
data circuits for the purpose of exchanging
information data. One way to determine applicable
requirements for listing of industrial equipment is to refer
to UL 61010-2-201, Safety requirements for electrical equipment
for measurement, control, and laboratory use –Part 2-201:
Particular requirements for control equipment, and/or
UL 61800-5-1, Adjustable speed electrical power drive systems –
Part 5-1: Safety requirements –Electrical, thermal and energy.
Read carefully the part in red.
 
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