Low Voltage Wiring

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jetbird

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I have a metal junction box that has mixed 208V, 120V and 24V AC. All wires are rated for 300V. Just outside the metal box I have a temperature controller that is fed 24V AC directly from a transformer in the metal box. Am I required to have conduit for the wiring connecting the temperature controller to the transformer in the metal box?

Thanks,

Jeff
 
I dont have my book in front of me at the moment but without internal dividers in the jbox I believe your install violates one of the subsections of 725.136.

If the 24VAC part is a cable assembly, you do not need conduit for it.
 
JFletcher said:
I dont have my book in front of me at the moment but without internal dividers in the jbox I believe your install violates one of the subsections of 725.136.

If the 24VAC part is a cable assembly, you do not need conduit for it.
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You are right. In the metal box I have solid state relays to control power to a 208V 3 phase fan motor. I was using 24AC to energize the relay, but I can switch to 120V. Additionally, I can scrap the 24V AC transformer, and power the temperature controller with 120V AC. Would this mitigate my issue if I no longer have a 24V AC transformer in the box, but only 120V and 208 3 phase?

Thanks,

Jeff
 
jumper said:
No code book, huh...so you are basically just guessing.;)

Tsk, tsk.......:D
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Sort of. :lol: I know somewhere in 725.136 forbids mixing class 2 and 3 circuits with class 1 unless certain exceptions/conditions are met. couldnt remember off the top of my head if it was just raceways or jboxes too.


jetbird said:
You are right. In the metal box I have solid state relays to control power to a 208V 3 phase fan motor. I was using 24AC to energize the relay, but I can switch to 120V. Additionally, I can scrap the 24V AC transformer, and power the temperature controller with 120V AC. Would this mitigate my issue if I no longer have a 24V AC transformer in the box, but only 120V and 208 3 phase?

Thanks,

Jeff
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If you eliminate the xfmr and class 2 circuit (the 24VAC) then your install will be compliant, tho you will need a nipple, short section of raceway, or a wiring method like NM or MC that doesnt require raceway coming out of that jbox to the temp controller. in other words, you cant wire them with like THHN w/o some protection.
 
JFletcher said:
Sort of. :lol: I know somewhere in 725.136 forbids mixing class 2 and 3 circuits with class 1 unless certain exceptions/conditions are met. couldnt remember off the top of my head if it was just raceways or jboxes too.
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Posting at MH forum without a code book is like “bringing a knife to a gunfight.” :cool:

Of course I still get killed here all the time even though I have mine.:D
 
jumper said:
Posting at MH forum without a code book is like “bringing a knife to a gunfight.” :cool:

Of course I still get killed here all the time even though I have mine.:D
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The original Mythbusters researched bringing a knife to a gunfight and found that if the knife user was within about ten feet of the gun user at the start they could usually stab the gun user before he could get his weapon out and fire.
 
GoldDigger said:
The original Mythbusters researched bringing a knife to a gunfight and found that if the knife user was within about ten feet of the gun user at the start they could usually stab the gun user before he could get his weapon out and fire.
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Did they suggest how the knifer was supposed to get within 10’ alive?
 
More details are needed. Class 2 or 3 circuits are quite often used to interact with lighting and power circuits via relays, contactors, solid state devices, etc. To do so they have to come close together at some point or you would never be able to use them in this manner. You can certainly have both types of circuits inside the same control cabinet, but may still need some sort of separation within that cabinet, mostly to avoid accidental contact with the higher energy circuit from the low energy control circuit.
 
jetbird said:
I have a metal junction box that has mixed 208V, 120V and 24V AC. All wires are rated for 300V. Just outside the metal box I have a temperature controller that is fed 24V AC directly from a transformer in the metal box. Am I required to have conduit for the wiring connecting the temperature controller to the transformer in the metal box?

Thanks,

Jeff
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All you need, Jeff, is a piece of thermostat wire. 24volt can be in free air. I would use plenum rated cable which is the insulation covering. Usually the low voltage terminals on the transformer are outside the box. To make the others here a little more happy you may want to use a transformer that attaches to the conduit box and leaves the low voltage terminals exposed for access. Most thermostat wire is rated for 300v so putting it in the high voltage area conforms.


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jetbird said:
You are right. In the metal box I have solid state relays to control power to a 208V 3 phase fan motor. I was using 24AC to energize the relay, but I can switch to 120V. Additionally, I can scrap the 24V AC transformer, and power the temperature controller with 120V AC. Would this mitigate my issue if I no longer have a 24V AC transformer in the box, but only 120V and 208 3 phase?

Thanks,

Jeff
Click to expand...

Mixing circuits is regulated in a raceway because disconnecting means for different circuits becomes impossible. In a controller there is one disconnect, the power source. Cut the one power source, all power goes down. With that, you can have any configuration of voltage the controlled apparatus desires as long as the insulation of the wires exceeds the highest voltage potential. If i can leave the controller with low voltage wire, I will save on the installation of same. Go to 120v, cost relatively quadruples.

Thanks for the exercise



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iquestionit said:
All you need, Jeff, is a piece of thermostat wire. 24volt can be in free air. I would use plenum rated cable which is the insulation covering. Usually the low voltage terminals on the transformer are outside the box. To make the others here a little more happy you may want to use a transformer that attaches to the conduit box and leaves the low voltage terminals exposed for access. Most thermostat wire is rated for 300v so putting it in the high voltage area conforms.


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Chances are at least a portion of that 24 volt control circuit has to enter the box somehow to connect to a relay, solid state control or something of that nature that controls some of the "power" circuitry, so it has to be allowed in there. You can still keep power and control conductors separated within that box, but at final connection to something like a relay they still can get pretty close to one another.
 
24VAC Temp Controller Power

24VAC Temp Controller Power

OK all post are very well stated where no code Chapter or article is shown since you have your book you can look them up. Use your craft knife to turn the pages make sure you cover it with your Journeyman Lead to ensure which craft then needs to tune the conroller in case 0-50 VDC And 120VAC are subject to craft rules from the Hall of the Labor Unions. Their steward may want a conversation with your lead or you.

Basically you will need to red line the drawing submit it to the owner for the changes, leave the copy of the the red line in the panel , red line the data sheet with any changes dated/signed/ and badge number, take your wet stone spit on it to clean the sharpened edge. Update the installation detail. Then take a look at Yosimity Sam make sure his smoking gun is tucked away and his code book is in his work bag.
 
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