24v control and 208v power wire in control cabinet

mavrck

Member
Location
ky
I have a question about installing different voltage in wire duct in a control cabinet.
I’m building a couple control cabinets that were mainly supposed to 120 /208 volt operation. Well the equipment showed and some now need 24 volt control and they added 3 drives with 24 input. There is no PLC everything is push button. Unfortunately there was no plan for this 24 volt application and I’m having to run 24 control wire beside 120/208 in wire duct. Can this cause EMI issues. Shielded cable aren’t a option due to routing the wire.
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
This is just in the control cabinet right?
You'll have to refer to the documentation in the drive or the 24V source.
On one hand you can (re)classify the 24V as class 1 and use chapter 3 wire (TFFN).
While that might be allowed, it might not work reliably unless you can get some separation.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Assuming you mean 24VDC?
There will be induction happening, but no way to tell if it will be enough to cause you troubles. I don’t understand the inability to use shielded wire though. It’s barely larger than unshielded.
 

mavrck

Member
Location
ky
I can’t use shielded because I have to go form the control cabinet to a separate hmi cabinet using 24 vdc relay then then to my drive. So in order to make this work as they want I would have to remove the shielding and jacket and split the wires to the 24volt and to the common , basically making the shielded cable useless
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
Hmmm thats not going to work as a class 1. Can you use a different 2 wire shielded cable for the relay?
Please post a diagram or a picture.
 

JR Martin

Member
Location
New Jersey
Occupation
Electrician
I have a question about installing different voltage in wire duct in a control cabinet.
I’m building a couple control cabinets that were mainly supposed to 120 /208 volt operation. Well the equipment showed and some now need 24 volt control and they added 3 drives with 24 input. There is no PLC everything is push button. Unfortunately there was no plan for this 24 volt application and I’m having to run 24 control wire beside 120/208 in wire duct. Can this cause EMI issues. Shielded cable aren’t a option due to routing the wire.
 

JR Martin

Member
Location
New Jersey
Occupation
Electrician
Code requires separate raceways for different voltages. Any kind of control wiring such as 4 to 20 ma must be in its own conduit. I would also check code as their is exceptions to this article.
 

ValeoBill

Member
Location
Wasaga Beach, Ontario
Occupation
Industrial Electrician
It's hard NOT to do in a typical panel, especially with "add-ons" and "improvements" after the original is built. Isolate the voltages as best you can. If they must cross, keeping the individual conductors 90' from one another will minimize noise/induction.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
What about a factory built roof top heating and ac unit? 480v contactors with 24 volt controls it's done all the time
That would be a factory assembled control panel or equipment that has been listed. And thermostat circuits are CL2. The manufacturer may provide a divider or compartment for the 24 volt control field wiring. However, what wiring they do external to that wouldn't necessarily have to be according to the NEC.

-Hal
 
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