Question regarding the isolation of low voltage and 277/

[JJWalecka]

I have a question regarding the isolation of low voltage, 120/208 and 277/480.
A 12 x 12 trough has various EMT's installed into it. The trough has 3" nipples installed to various panels. A few 3/4 Emts installed on the same unistrut and installed into the same trough is use for low voltage cable. The Belden cable is installed in the raceway to roof top units. Inside the trough the EMT is changed to Greenfield by rigid coupling. The Greenfield is sleeved through the same nipple as the Branch circuits for the roof top units. The Greenfield is taped on the inside and outside for anti short purposes.
It is my understanding that a isolation barrier should be installed between This low voltage cable and the 277/480.
Would Greenfield used in the application be considered an approved barrier?
The low voltage would not have a barrier in the panel.
Any opinions would be appreciated.

Justin W.

 

[iwire]

Re: Question regarding the isolation of low voltage and 277/

The Belden cable most likely contains class 2 circuits and either has to have a barrier between it and class 1 circuits or the class 2 circuit must be treated as a class 1 circuit from start to finish.

If you mean flexible metal conduit by the term greenfield then that is a suitable barrier.

Any raceway would be a suitable barrier.

 

[JJWalecka]

Re: Question regarding the isolation of low voltage and 277/

Iwire thank you again for your time.
I read in 725.26 B1 that Class one circuits and power supply circuits shall be permitted to occupy the same cable, enclosure, or raceway only where the equipment powered is functionally associated.
Thank you.

Justin W.

 

[iwire]

Re: Question regarding the isolation of low voltage and 277/

Originally posted by justinjwalecka:
I read in 725.26 B1 that Class one circuits and power supply circuits shall be permitted to occupy the same cable, enclosure, or raceway only where the equipment powered is functionally associated.

Yes when that applies no special barriers are required.


Take a look at 725.52(A)Exception No. 2 for another option.

 

[JJWalecka]

Re: Question regarding the isolation of low voltage and 277/

408.3a2 mentions barriers in switchboards.

725.55b states that class 2 and class 3 circuits shall be permitted to be installed together with the conductors of electric light, power, class 1, non-power-limited fire alarm and medium power network-powered broadband communications citcuits where they are separated by barrier.

725.55(J)other applications. For other applications, conductors of Class 2 and Class 3 circuits shall be separately by at least 2 inches from conductors of any electric light, power, Class 1 non-power-limited fire alarm or medium power network-powered broadband communications circuits unless one of the following conditions is met.

725.55(J)(1)(a)Either all of the electric light, power, Class 1 non-power-limited fire alarm or medium power network-powered broadband communications circuit conductors or
(b) all of the Class 2 and Class 3 circuit conductors are in a raceway or metal-sheathed, metal-clad, non- metallic-sheathed or type UF cables.

Is these code articles where you deciphered that Flexible metal conduit would be and approved barrier?
Could you provide me with more?
I will continue searching. Thank you

Justin W

 

[iwire]

Re: Question regarding the isolation of low voltage and 277/

Originally posted by justinjwalecka:
408.3a2 mentions barriers in switchboards.

That has nothing to do with class 1, 2 or 3 circuits.

Originally posted by justinjwalecka:
Is these code articles where you deciphered that Flexible metal conduit would be and approved barrier?
Could you provide me with more?
I will continue searching. Thank you

Justin W

No deciphering necessary any listed raceway is a suitable barrier.

If a listed raceway is not a suitable barrier it would be dangerous to run THHN in EMT with class 1 circuits inside.

The reason for the separation of class 1 and 2 circuits is so that class 1 voltage and current levels can not be imposed on the class 2 or 3 circuits.

I have seen this happen and it ain't pretty.

Next time your buying deli meat look at the scale, it will have a class 2 data cable and a 120 supply.

In some cases the data line is routed inside the deli case with the 120 volt line. Well the 120 shorted melted and fried right into the data line.

This destroyed other scales and the hub in the computer room.

Had either one of these circuits been in a separate raceway it would not have happened.

Also if you ever get the opportunity to install Square D power link breakers you will find that they require class 2 wiring inside the panel. In that case non-metallic flexible tubing is used as the barrier.

 

[JJWalecka]

Re: Question regarding the isolation of low voltage and 277/

Iwire Thank you

Justin W.