Class 2 circuits

wireday

Senior Member
This is a speed indicator/encoder wheel, It was made up for a machine at a manufacturing plant. I've been asked to make up another one. The control box has 120 volt power feeding it from the cord on the left,The encoder wire on the right is class 2 wiring. They both attach to the back of the controller in the box. My question is this in violation of art:725.136, The controller is capable of being powered by 24VDC. If this is a violation would I be better to use a 24VDC wall plugin transformer instead of the 120V? IMG_5805 (1).JPG
 

wireday

Senior Member
Thanks Gold Digger, I was thinking about buying a wall wart 24VDC class 2 transformer to power this instead of the 120V. By NRTL do you mean a non removable class 2 label on the wall wart? . Im guessing that you are saying the picture is a violation? If I use the wall wart the whole thing would be class 2
 

Macbeth

Member
Location
Livonia NY
Case #1
If the CL2 power source is a marked as a CL2 power supply then the circuits max rating is:
Max voltage is 150vac/dc and limited to 100w

Case #2
If the power supply is not rated as CL2, then a current limiting over current protection device must be used then:
Max voltage is 30vac/and 60vdc and limited to 100w

This is why all most every PS under 100w are rated as CL2. Now it you have a 300w PS you must use a current limiting over current protection device on every wire that exits the panel to limit power to 100w.
 

GoldDigger

Moderator
Staff member
Thanks Gold Digger, I was thinking about buying a wall wart 24VDC class 2 transformer to power this instead of the 120V. By NRTL do you mean a non removable class 2 label on the wall wart? . Im guessing that you are saying the picture is a violation? If I use the wall wart the whole thing would be class 2
I was trying to be appropriately generic in specifying a label from a Nationally Recognized Testing Laboratory (NRTL) instead of casually saying a UL label. :)
And while I am quibbling, the wall wart is a DC power supply and not just a transformer. Some low voltage DC supplies, like for powering shavers, may not even contain a transformer.
 

wireday

Senior Member
Thanks Gold Digger, kinda like the inexpensive cell phone chargers. What are your thoughts on the metal enclosure in this picture,would it require a EGC or should I try to find non metal enclosures?
 

GoldDigger

Moderator
Staff member
The key, I think, is the "likely to become energized" condition. Especially if the wall wart does not contain an EGC, I see no need to provide one.
(Some bricks, as distinct from wall warts, have a three wire cord and have an EGC in the output cord too.)
Your choice on whether a plastic enclosure would make you feel better.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
See 715.136(D). There are many installations where the Class 2 wiring must be in the same enclosure as the power wiring and this section gives you the conditions that you much comply with where you have both circuits in a common enclosure.
 

wireday

Senior Member
Mac
Case #1
If the CL2 power source is a marked as a CL2 power supply then the circuits max rating is:
Max voltage is 150vac/dc and limited to 100w

Case #2
If the power supply is not rated as CL2, then a current limiting over current protection device must be used then:
Max voltage is 30vac/and 60vdc and limited to 100w

This is why all most every PS under 100w are rated as CL2. Now it you have a 300w PS you must use a current limiting over current protection device on every wire that exits the panel to limit power to 100w.
[/QUOTE
Case#1 in this case the class 2 power supply is coming from the controller itself. It is marked Class 2. If your saying its max is 150V AC 100watt max, would that make the line voltage 120V AC and this field wire encoder compatible, and up to code?
 

Macbeth

Member
Location
Livonia NY
The 120vac entering your panel would be best described as a "Power Circuit" unless there was a "power Limiting Device" which limited the potential power to 100w before it entered your panel. I believe you have a cord that plugs in to the wall plug than enters your panel, there fore it can not be a CL2.

So the 120v connects to the controller then the controller outputs voltage to your encoder. since the controller is CL2 rated and marked the encoder can use CL2 wiring. The power circuit and the CL2 Circuit may "Mix" because they are "Related". However wires of different insulation class need to be separated. So if your CL2 wire touches the 120v power wire the CL2 wire needs to be the same insulation class as the 120v wire. This does not mean the cl2 cable needs to be changed, just insulated, such as two wraps of electrical UL rated Tap, or sleeved with UL rated tube..
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
The control box has 120 volt power feeding it from the cord on the left,The encoder wire on the right is class 2 wiring. They both attach to the back of the controller in the box. My question is this in violation of art:725.136,
As was pointed out in your other thread on this same question, 725 has nothing to do with this.

Installing the listed controller in a box doesn't change anything. The 120V line cord and connector for the encoder cable is how the controller came from the manufacturer. You are only running those cables out of the box.

-Hal
 

wireday

Senior Member
The 120vac entering your panel would be best described as a "Power Circuit" unless there was a "power Limiting Device" which limited the potential power to 100w before it entered your panel. I believe you have a cord that plugs in to the wall plug than enters your panel, there fore it can not be a CL2.

So the 120v connects to the controller then the controller outputs voltage to your encoder. since the controller is CL2 rated and marked the encoder can use CL2 wiring. The power circuit and the CL2 Circuit may "Mix" because they are "Related". However wires of different insulation class need to be separated. So if your CL2 wire touches the 120v power wire the CL2 wire needs to be the same insulation class as the 120v wire. This does not mean the cl2 cable needs to be changed, just insulated, such as two wraps of electrical UL rated Tap, or sleeved with UL rated tube..
The controller is a Automation Direct model CTT-AN-A120 the encoder a TRD-S/SH
In looking the controller over it does not indicate Class 2, it does state UL and open type process control. output is 12VDC @ 100ma
so if its not labeled C2 do I just go buy the table in chapter 9? Also I do not know the rating on the encoder wiring,by UL listed sleave,what are examples of that, thank you
 

wireday

Senior Member
As was pointed out in your other thread on this same question, 725 has nothing to do with this.

Installing the listed controller in a box doesn't change anything. The 120V line cord and connector for the encoder cable is how the controller came from the manufacturer. You are only running those cables out of the box.

-Hal
Thank you Hbiss,
The controller is a Automation Direct model CTT-AN-A120 the encoder a TRD-S/SH
In looking the controller over it does not indicate Class 2, it does state UL and open type process control. output is 12VDC @ 100ma
thank you
 

wireday

Senior Member
Thank you Hbiss,
The controller is a Automation Direct model CTT-AN-A120 the encoder a TRD-S/SH
In looking the controller over it does not indicate Class 2, it does state UL and open type process control. output is 12VDC @ 100ma
thank you
[/QUOTE

Am I over thinking this? If I am feeding the controller 120V and the encoder field wire is connected to the controller , Is it the controller is not itself a power supply? therefore no C2 listing or spacing is needed? I would be installing the components into a box with cord and switch. Thank you
 

wireday

Senior Member
I just got a chance to look at the encoder model TRD-S2000BD it says power supply class 2 8-26.4V. the controller that I mentioned before has no wording of class 2 thank you
 
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