Line & Low Voltage in the same enclosure

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cdcengineer

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We are running an energy management system to some guest rooms (Inncom). The system devices are line voltage switches, but they have a communications link between all devices. NEC (300.3(C)(1)) requires that if we are housing line and low voltage wiring in the same enclosure the insulation must meet the maximum ckt voltage applied to any conductor.

Has anyone had experience with this sort of application? A friend of mine ran Cat 6 cable, and provided a shrink wrap insulation around the cable to meet insulation req'mts. This seems like too much labor. I'm thinking a belden cable of some sort would cost about the same, yet be less labor intensive.

Thanks,

DC
 

cdcengineer

Senior Member
Can anyone tell me where I might find the definitions of the different classifications of wiring ie I, II, and III?

Thx
 

cdcengineer

Senior Member
Great thanks..

I'm just trying to determine which system I am dealing with. I see a class 1 system is defined along with it's power source. The class 2 & 3 power sources are a little difficult to determine. I think we have a class 1 system, but just want to verify.
 

Dennis Alwon

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Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Great thanks..

I'm just trying to determine which system I am dealing with. I see a class 1 system is defined along with it's power source. The class 2 & 3 power sources are a little difficult to determine. I think we have a class 1 system, but just want to verify.

Often times the transformer or the equipment has what class it is. I still have no idea how to tell class II from Class III
 

cdcengineer

Senior Member
So the reason I posted this in the first place was because the inspector had called out an installation where there was 120V, single phase connected to a switch and in the same enclosure there was CAT 6 providing a communications link at 24V connected to the same switch. The CAT 6 insulation is rated at 300V. There was no room for partition in the box. I now believe Inncom to be a class 1 system.

I had been under the impression that the reason it was called during inspection was because I always believed the insulation had to match (ie MC cable at 600V = Belden cable at 600V).

This was called out for hundreds of units during earlier phases of construction and the crew went thru and installed heat shrink insulation over the CAT 6. This included opening hundreds of devices.

We were not that unlucky contractor, but I am involved with the team doing the next phase. The owner wants to make sure we don't run into the same hassle.

The reason I'm digging thru this is because 600V Belden cable is nearly 10x the price of non-plenum CAT 6. We want to save money while of course doing it right.

Now, after reading 300.3(C)(1) closely (along with the handbook notes below the article), I realize we should be Aok with CAT 6 at 300V.

Any takers??
 

raider1

Senior Member
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Location
Logan, Utah
So the reason I posted this in the first place was because the inspector had called out an installation where there was 120V, single phase connected to a switch and in the same enclosure there was CAT 6 providing a communications link at 24V connected to the same switch. The CAT 6 insulation is rated at 300V. There was no room for partition in the box. I now believe Inncom to be a class 1 system.

I had been under the impression that the reason it was called during inspection was because I always believed the insulation had to match (ie MC cable at 600V = Belden cable at 600V).

This was called out for hundreds of units during earlier phases of construction and the crew went thru and installed heat shrink insulation over the CAT 6. This included opening hundreds of devices.

We were not that unlucky contractor, but I am involved with the team doing the next phase. The owner wants to make sure we don't run into the same hassle.

The reason I'm digging thru this is because 600V Belden cable is nearly 10x the price of non-plenum CAT 6. We want to save money while of course doing it right.

Now, after reading 300.3(C)(1) closely (along with the handbook notes below the article), I realize we should be Aok with CAT 6 at 300V.

Any takers??

A class 1 system is required to be installed using a Chapter 3 wiring method so CAT 6 cable would not be acceptable.

I really doubt that what you have is a Class 1 circuit most likely you will have a Class 2 circuit.

Class 2 & 3 Circuit conductors can be installed in an enclosure or box with power conductors in accordance with 725.136(D) (2008 NEC section number).

Chris
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I had been under the impression that the reason it was called during inspection was because I always believed the insulation had to match (ie MC cable at 600V = Belden cable at 600V).
Each insulation rating must merely equal or exceed the voltage present, not the other cables' rating.
 
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