Mixing power & low voltage - ECN Electrical Forums

I am working on the site of a new sewage plant. There are several man holes, hand holes and pull boxes where security, phone, PA system, 480V feeders, 120V control wiring and other 480V circuits share the same enclosure with no divider. The runs were designed this way by the electrical engineer. When we questioned the engineer on the issue of code compliance he said that because it was an industrial installation that it was OK. What do you think?

I don't think there is anything in the NEC prohibiting mixing current-carrying and signal cables or conductors. However, there will be noise from the current-carrying conductors that could (will) interfere with the signal cables. I'd tell the EE to try again.

It's OK anyway! Only requirement is that "System" is identified.

Br-Or-Ye-GRAY or HA-HB-HC-HN

Bk-Rd-Bl-WHITE or LA-LB-LC-LN

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200.6(D) Grounded Conductors of Different Systems.

Where conductors of different systems are installed in the same raceway, cable, box, auxiliary gutter, or other type of enclosure, one system grounded conductor, if required, shall have an outer covering conforming to 200.6(A) or 200.6(B). Each other system grounded conductor shall have an outer covering of white with a readily distinguishable, different colored stripe other than green running along the insulation, or shall have other and different means of identification as allowed by 200.6(A) or (B) that will distinguish each system grounded conductor.

Commentary:
The requirements found in 200.6(D) are essentially the same since the 1987 edition of the NEC. However, these requirements are often misapplied. As Exhibit 200.2 shows, if grounded conductors of different systems are present in the same enclosure, these grounded conductors must be distinguishable, such as by different colors. Careful study of 200.6(D) reveals what Exhibit 200.2 shows, that is, where one system uses a white or gray insulation for the grounded conductor, the other system must use an identification different from the color selected for the first system colored insulation. For example, where one system uses white for the grounded conductor, the second system must use a different color or marking such as gray or white with a stripe.

And,
210.4(D) Identification of Ungrounded Conductors.

Where more than one nominal voltage system exists in a building, each ungrounded conductor of a multiwire branch circuit, where accessible, shall be identified by phase and system. This means of identification shall be permitted to be by separate color coding, marking tape, tagging, or other approved means and shall be permanently posted at each branch-circuit panelboard.

[This message has been edited by e57 (edited 03-22-2005).]

Doh, I missed the part with PA, security and phone, thats NOT cool...... Not safe either. Phone could carry 480 outside the facility.

Only Power-limited fire alarm from what I can see off the top of my head can do this in limited situations.

As for the Industrial situation.... Unless the site is exempt somehow from building codes. There are a few types of industry that are, others can tell you what they are.

[This message has been edited by e57 (edited 03-22-2005).]

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I don't think there is anything in the NEC prohibiting mixing current-carrying and signal cables or conductors.

See 800.52(A)(1).

I don't have my code book handy to reference the correct section #, but isn't there a requirement that all conductors in a raceway must have the same insulation or voltage rating.

This generally prevents pulling a Beldon-style communication cable in the same conduit with THHN, THW, etc.

None of this may apply in manholes though.

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National Electrical Code, NFPA 70-2002 (Emphasis added)
ARTICLE 800 Communications Circuits
800.52 Installation of Communications Wires, Cables, and Equipment.
Communications wires and cables from the protector to the equipment or, where no protector is required, communications wires and cables attached to the outside or inside of the building shall comply with 800.52(A) through (E).
(A) Separation from Other Conductors.
(1) In Raceways, Boxes, and Cables.
(c) Electric Light, Power, Class 1, Non–Power-Limited Fire Alarm, and Medium Power Network-Powered Broadband Communications Circuits in Raceways, Compartments, and Boxes. Communications conductors shall not be placed in any raceway, compartment, outlet box, junction box, or similar fitting with conductors of electric light, power, Class 1, non–power-limited fire alarm or medium power network-powered broadband communications circuits.

Brooke Stauffer of NECA has also written an article on this topic for NFPA called, "You Gotta Keep 'Em Separated". If I can find it on the NFPA website I'll post a link.

[This message has been edited by safetygem (edited 03-23-2005).]

OK. Well I looked and it appears the Brooke Stauffer article is not currently available on the web.

Here is the full title:
YOU GOTTA KEEP ‘EM SEPARATED:
For Safety and Performance Sake, Line Voltage
and Low Voltage Systems Must Be Kept
Separate. Here's Why and How.

The article was in the September 2000 issue of the NECDigest. If you are interested and you contact NFPA customer service (1-800-344-3555) they may send you a copy.

OK... now onto a new comment.

master66, is this WWTP an aerobic plant or an anaerobic plant? The reason I'm asking is that you mentioned the presence of "several man holes" on the site.

Typically at a plant of the anaerobic design, many of the below grade spaces will be classified. You should thoroughly review NFPA 820, Fire Protection in Wastewater Treatment and Collection Facilities for all of the wiring requirements in the facility.

Now granted I hope the electrical engineer reviewed this standard, but, it has been my experience that they usually don't even know about it. [Linked Image]

Just something to consider. If you have any questions, about 820, feel free to post and I'll see if I can answer them.

[This message has been edited by safetygem (edited 03-23-2005).]

safetygem, What is the difference between the two types of wwtp that you mentioned?

To everyone else, thank you for your comments.

My supervisor & I were talking about this subject again today and he mentioned that our company is bidding on another wwtp with the same design (mixing low voltage & communications with power wiring) and it is by a different engineer. He also said that the engineer referred him to a publication that allows this at a wwtp. I intended to find out what the publication was before I left today but I forgot. I"ll try to remember for Monday.

Master66... sorry, I forgot to check back in on this thread.

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What is the difference between the two types of wwtp that you mentioned?

Anaerobic plants have "digesters" that break down the sludge in an enclosed space where there is very little oxygen present and as a by-product produce a fairly large amount of hydrogen sulfide and methane gases. Normally you can tell this type of design because of the digesters, which are large (usually circular) buildings with floating roofs. Because of the expected levels of gas there are a large number of locations at the plant that will be classified.

Aerobic plants can have classified areas, but, many few locations at the plant will be a concern. This style plant has large mixing tanks and lagoons that "churn" up the water and use that action to break down the sewage. Because the actual digestion process takes place in the open and in the presence of oxygen there are very few classified areas.

Let me know if you are interested and I'll have Bill post a photo of each design.

ELECTRICAL ENGINEERS ARE LIKE WEATHERMEN (HIT AND MISS)

Article 90.2(B) cover's the things the NEC does not cover, and a sewer plant is not one of them. I worked for a electric utility for 25 years so knew utility companies were exempt, and that mines were also. I once did a upgrade at a cable company facility once with all them huge satalite dishes (doing this while employed for electric utility moonlighting), upgraded service, several outlet's and lighting, couple of A/C units etc. and I pulled a permit of course and when the inspector came he wasn't sure if I even needed to pull a permit beings it was a communications type of building, but we figured with all new electric stuff good idea but later on the racks and stuff that cable company was going to put in would be exempt.
but as for comm. wiring with 480v wiring I have spent some time in steam/nuclear/hydros power plants and have mixed them and not have any problem's, but then there been times when did get interference and have to run seperate conduit along side the cable tray for the comm. circuits.
BUT any how a sewer plant is not exempt from the NEC thats for sure.
this board is good, sure makes you look up stuff..

[This message has been edited by highvoltageguy (edited 03-27-2005).]

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Originally posted by northstar:

ELECTRICAL ENGINEERS ARE LIKE WEATHERMEN (HIT AND MISS)

Worse... with the attitudes of some, they're like attituded AHJ's without the badges. [Linked Image]

"What do you mean you won't do it that / my way? What is this "Code" of which you speak?"