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AudibleSolutions
01-26-2005, 06:22 PM
Stupid question # 2.

1. I have forgotten the citation in NEC whereby in is now possible to have low voltage and high voltage in the same box. Any recollection?

2. That same citiation also tells of the minimum distance between the low and high voltage wires. What is it?

Alan

AudibleSolutions
01-26-2005, 06:49 PM
Article 725:55 and 1/4 inch separation between class 2 conductors and high voltage.

Thank you, Lutron

Alan

LarryFine
01-26-2005, 09:17 PM
Alan touched upon it; no more answering your own questions! :lol:

The simple answer is that power and low-voltage conductors must be separated by a barrier. I like the boxes that have an electric box and a low-voltage (backless) box "Siamesed" together for new work.

You can also get low-voltage boxes that can be added to electrical boxes. Another generalization is that, when mixing conuctors, all of the insulation must be rated for the higher voltage.

Here are NEC excerpts that may be relevant:

725.54 Installation of Conductors and Equipment in Cables, Compartments, Cable Trays, Enclosures, Manholes, Outlet Boxes, Device Boxes, and Raceways for Class 2 and Class 3 Circuits. Conductors and equipment for Class 2 and Class 3 circuits shall be installed in accordance with 725.55 through 725.58.

725.55 Separation from Electric Light, Power, Class 1, Non–Power-Limited Fire Alarm Circuit Conductors, and Medium Power Network-Powered Broadband Communications Cables.

(A) General. Cables and conductors of Class 2 and Class 3 circuits shall not be placed in any cable, cable tray, compartment, enclosure, manhole, outlet box, device box, raceway, or similar fitting with conductors of electric light, power, Class 1, non–power-limited fire alarm circuits, and medium power network-powered broadband communications circuits unless permitted by 725.55(B) through (J).

(B) Separated by Barriers. Class 2 and Class 3 circuits shall be permitted to be installed together with Class 1, non–power-limited fire alarm and medium power networkpowered broadband communications circuits where they are separated by a barrier.

(C) Raceways Within Enclosures. In enclosures, Class 2 and Class 3 circuits shall be permitted to be installed in a raceway to separate them from Class 1, non–power-limited fire alarm and medium power network-powered broadband communications circuits.

(D) Associated Systems Within Enclosures. Class 2 and Class 3 circuit conductors in compartments, enclosures, device boxes, outlet boxes, or similar fittings shall be permitted
to be installed with electric light, power, Class 1, non–power-limited fire alarm, and medium power networkpowered broadband communications circuits where they are introduced solely to connect the equipment connected to Class 2 and Class 3 circuits, and where (1) or (2) applies:

(1) The electric light, power, Class 1, non–power-limited fire alarm, and medium power network-powered broadband communications circuit conductors are routed to maintain a minimum of 6 mm (0.25 in.) separation from the conductors and cables of Class 2 and Class 3 circuits.

(2) The circuit conductors operate at 150 volts or less to ground and also comply with one of the following:

a. The Class 2 and Class 3 circuits are installed using Type CL3, CL3R, or CL3P or permitted substitute cables, provided these Class 3 cable conductors extending beyond the jacket are separated by a minimum of 6 mm (0.25 in.) or by a nonconductive sleeve or nonconductive barrier from all other conductors.

b. The Class 2 and Class 3 circuit conductors are installed as a Class 1 circuit in accordance with 725.21.

Theaterworks
01-28-2005, 06:25 AM
Larry, I can see you will be an excellent resource for us non-electrian types. Thanks for your contribution.

Now, can you help me figure out why that light in my hallway flickers once in a while.....?

The8thst
01-28-2005, 10:53 AM
I thought there was another clause in the code where low voltage and high voltage can be in the same box without a barrier IF the low voltage wire is a proprietary control wire for the high voltage load. The lowvoltage wire must directly control the load...

For example:
A Keypad wire to a RPM in a Homeworks system
The maestro bus LV wire in the same box as the maestro switch itself.

It does not apply to:
An emitter wire in the same box as a GraphicEye because they are not both part of the same proprietary system even though the emitter wire is controlling the GraphicEye.




This is an are where I tend to abide by the "safer than sorry" theory and still keep the two wires seperated to minimize the prospect of having issues with the inspector, but since it is a forum for pros..... and since Larry is around..... why not clarify?

LarryFine
01-28-2005, 10:53 PM
Maybe here:

725.26 Conductors of Different Circuits in the Same
Cable, Cable Tray, Enclosure, or Raceway. Class 1 circuits
shall be permitted to be installed with other circuits as
specified in 725.26(A) and (B).


(A) Two or More Class 1 Circuits. Class 1 circuits shall
be permitted to occupy the same cable, cable tray, enclosure,
or raceway without regard to whether the individual
circuits are alternating current or direct current, provided
all conductors are insulated for the maximum voltage of
any conductor in the cable, cable tray, enclosure, or raceway.


(B) Class 1 Circuits with Power Supply Circuits. Class 1
circuits shall be permitted to be installed with power supply
conductors as specified in 725.26(B)(1) through (B)(4).

(1) In a Cable, Enclosure, or Raceway. Class 1 circuits
and power supply circuits shall be permitted to occupy the
same cable, enclosure, or raceway only where the equipment
powered is functionally associated.

(2) In Factory- or Field-Assembled Control Centers.
Class 1 circuits and power supply circuits shall be permitted
to be installed in factory- or field-assembled control
centers.

(3) In a Manhole. Class 1 circuits and power supply circuits
shall be permitted to be installed as underground
conductors in a manhole in accordance with one of the
following:

(1) The power-supply or Class 1 circuit conductors are in a
metal-enclosed cable or Type UF cable.

(2) The conductors are permanently separated from the
power-supply conductors by a continuous firmly fixed
nonconductor, such as flexible tubing, in addition to the
insulation on the wire.

(3) The conductors are permanently and effectively separated
from the power supply conductors and securely
fastened to racks, insulators, or other approved
supports.

(4) In cable trays, where the Class 1 circuit conductors and
power-supply conductors not functionally associated with
them are separated by a solid fixed barrier of a material
compatible with the cable tray, or where the power-supply
or Class 1 circuit conductors are in a metal-enclosed cable.

Ghost
01-29-2005, 11:41 PM
There's some neat courses you can take for this stuff.

The NFPA has a Low Voltage Wiring Seminar you can attend - it's a 1 day event and costs about $330 for non-members. I went to one in Orlando this past December, the instructor was great, he knew the code book like the back of his hand. I got a NEC 2005 code book with tabs and a workbook of the course as well. It was pretty neat.

They also have some other seminars as well:
http://www.nfpa.org/catalog/product.asp?pid=LV1