Article 725

[grecon]

I am a Controls Engineer/systems integrator for automated lumber handling company.
I spend most my time designing industrial control panels and doing the PLC programming.(Panels are all UL 508A listed)

I have recently also started to involve myself with the electrical installation of the industrial equipment.

After studying the electrical installation practices and a quick look through the 2005 NEC code book, I have determined that we may be in violation of a few code rules. In particular Article 725 and Article 800.

The problem I see is with the cabling for Class 1 circuits and PLC communications from control panel to equipment.

Before I go too far into detail about the problems I see, let me ask this question:

Are there rules that in NFPA79 standards that supercede the NEC rules so that some or all of the violations I see are actually allowed?

I need to know this so I can determine if I need the NFPA79 standards book or do a major overhaul on our installation practices.

Thanks in advance.

 

[petersonra]

Re: Article 725

generally, NFPA79 applies to the equipment itself, while NEC applies to the installation thereof.

this does not mean you can completely ignore NEC requirements because you have to accomodate them in the equipment design.

I think you would need to give us some specifics to be able to tell you more.

 

[grecon]

Re: Article 725

Here are a few examples. I apologize for the lengthy reading.

Example #1
10 amp 24VDC Class 1 circuit from control panel.. Feeds a 10 conductor cable going to a Sensor Actuator Block. (molded self contained junction box for sensors etc)
Manufacturer of Sensor Actuator Control Block supplies the cable. Has molded 12 pin connector.
The cable consists of 11 conductors. 3 of them are 18 AWG for power and ground and the other 8 are for PLC Inputs and outputs.
Cable markings: ?PUR/PVC 8x0,34/3x0,75 ?LN0085957- 001041485 CE?
An additional marking is added after the molded connector is added
?Tested at 500V/DC 1508268 43804/80988?

Problem
1. Cable has 20 AWG wire. I do not see where 20AWG is allowed. 725.27(A) allows 16 and 18 AWG
2. Class 1 power is 10 amps. Minimum wire size for Class 1 circuit at 10 amps 16 AWG 725.23
3. Cable is not rated for 600 volts nor is it marked for Class 1 usage 725.27(B)

Example #2
From this same SACB, a cable that consists of four 22 AWG conductors is used to connect photo-eyes and solenoids.
The cable travels about 2 feet from SACB, enters cable tray, later exits cable tray and travels 2 ? 6 feet to device. The only support is the cable tray. There is no support after or before cable tray.
Cables are mechanically protected by machine.
Cable markings: C(UL)US 300 volts AC/DC 4 amps 80?C 300V series B1

Problem
1. Cable has 22 AWG wire. I do not see where 22AWG is allowed. 725.27(A) allows 16 and 18 AWG
2. Class 1 power is 10 amps. Minimum wire size for Class 1 circuit at 10 amps 16 AWG 725.23
3. Cable is not rated for 600 volts nor is it marked for Class 1 usage 725.27(B)
4. Can this cable be exposed if it is not crush or impact resistant?

Example #3
Some contractors used cable tray to run cables.
They placed a barrier inside the cable tray and ran motor cables on one side and remote-control and communications on the other side.
The remote-control cables are the Cables from the first 2 examples plus a cable that went to the push button panel. It is the same Class 1 circuit.
The multi-conductor cable to push button panel was marked:
VDE-REG-NR 7014 PBFREE CE 609412/433
The motor cables are Type TC-ER. 336.10(7)
The 3 communications cables were marked:
Belden 3084A Devicebus shielded. (UL) CL2 or CMG or AWM 600V
Belden BlueHose shielded (UL) CM or CL2 or AWM 2464
Coleman 96263 UL listed Type CMR FT-4
The cable tray ran behind two of the remote panels. The cables exited the bottom of the tray and looped about 2 feet to the panel where the cables entered the side. (Machine was 30? in the air including panel)

Problem
1. Communications cable, Class 2 circuits, mixed with 10 amp 24VDC Class 1 circuit. 725.55(H)
2. Class 2 circuit cables suspended from cable tray to control panel. 725.61(4)
3. Class 1 circuit cables suspended from cable tray to control panel. 725.27(C) 392.3(A) 336.10(7)
4. Multi-conductor cable to push button panel is not Type TC 725.3(E) 392.3(A) 336.10
5. No voltage ratings on 2 of the communication cables. Can they be ran together? 725.56 says ?Yes?

392.5(E) has me a bit confused. ?Multiconductor cable rated 600 volts or less shall be permitted in the same cable tray?
I am assuming as long as they meet all the other code requirements.

Thanks again for your response.

 

[tom baker]

Re: Article 725

The requirement for separation of control circuits from power and lighting is widely misunderstood and ignored. At least greycon understands the rules are in Art 725! If you are referring to Device Net circuits, then AB has an excellent publication that discussed the application from an NEC point of view: DeviceNet Cable System Planning and Installation Manual, cat DN-6.7.2, it will be available as a download from the AB/Rockwell automation bookstore.
It appears that the installation described is a violation of various code rules.

 

[kiloamp7]

Re: Article 725

Of all the different applications mentioned in NEC, that I deal with, Art. 725 is probably the one that I am least comfortable with.

 

[hbiss]

Re: Article 725

Where is this equipment manufactured? Is it listed by any testing organization?

From the description of the cables and their printed designations there is nothing to indicate that they are listed by themselves. In my opinion they would be part of the machine assembly because of the moulded plug (you have no choice other than to use these supplied cable assemblies) and they would be included in the machine listing. If that is the case it supercedes the NEC.

-Hal

 

[petersonra]

Re: Article 725

I don't like the phrase "supercedes the NEC". This implies something that is not actually true. What is true is that the NEC does not apply to everything that has wires. Sometimes you have to think a little to determine just what applies to what.

 

[pierre]

Re: Article 725

I, like Hal, believe that NFPA 79 may have precedent over the NEC on this type of installation. If the equipment and wiring are part of a 'listed assembly' the installation has been tested to performance by the listing company and is not under the purview of the NEC.

If it is not a 'listed assembly', Tom has said it very well.

Pierre

 

[petersonra]

Re: Article 725

Originally posted by pierre:
I, like Hal, believe that NFPA 79 may have precedent over the NEC on this type of installation.

I am not sure I like the phrasing but I agree with the sentiment. It may be that the NEC just does not apply to this situation.

However, the UL listing aspect is another thing altogether. UL does not list the machine, only the control panel. The cables are not part of the control panel so are not part of the listing.

However, regardless of any UL listing, the machinery is covered by NFPA79 rather than the NEC. The NEC covers power drops to the machine and some other things (like motor wiring and EGC) but I would say that proximity switch cables are covered under NFPA79 rather than NEC.

 

[grecon]

Re: Article 725

Thanks for every ones response.

I have spent the better part of 3 days doing nothing but reading code, e-mailing and talking to manufacturers and vendors.

Everyone agrees that the machine wiring we practice is par with everyone else in the industry and no one has problems with inspections. But no one has been able to tell me why these practices are allowed, until today. I hope NFPA 79 helps me out. I am not comfortable putting a system in a plant not knowing if it is code compliant or not.
FYI the machines we build are for furniture and flooring plants. The reason for all this research into electrical code is because we are going to begin using multi-conductor cables and cable tray instead of pipe.

 

[grecon]

Re: Article 725

I think I figure it out. (I hope. This is exhausting)

The answer for my problems was with NFPA 79.
Since we are an OEM manufacture of industrial machinery I believe this must apply to us.

NFPA 79 applies to the electrical installation of industrial machinery starting at the point of connection of the supply to the electrical equipment of the machine. If no provisions are made in NFPA 79 to a wiring method then you must use NFPA 70. (very rough summary of rule)

I read the NFPA 79 code book cover to cover and created a document that explained each and every Class 1, Class 2 and communication wiring method that we practice. (thank goodness)
NFPA 79 made no, or little reference to power cables, so for our motors we had to use NFPA 70 (which we knew we were o.k. with already)

By Article 725 of NFPA 70 alone our electrical inspections would fail. But by NFPA 79 we appear to be good.

Thanks for you help in this matter.
I have learned more about code in the last 3 weeks....

If you are interested in my findings with NFPA 79 and what I concluded, please let me know.
I would like as much input as possible to make sure I am correct.

Grecon

 

[grecon]

Re: Article 725

FYI
After looking at NFPA 79 and lengthy discussions with vendors I have determined that it is NFPA 79 that allows us to wire the equipment as we do.
Following is a very brief summary

1.1.1 NFPA 79 applies to the electrical equipment of industrial machinery operating at 600 volts or less and commencing at the point of connection of the supply to the electrical equipment of the machine.

1.5 NFPA 70 must be observed for any specific provisions that are not made in NFPA 79

Chapter 1 with Annex C determines that our material handling equipment can apply NFPA 79.


7.2.4.2.2 Conductors size 18, 16 and 14 AWG shall be considered protected by an overcurrent device of 20 amps or less


7.2.14 You can use 1 overcurrent protection device to protect different conductors of a control circuit.

13.6.2 Control circuit conductors shall not be smaller than 18 AWG where part of a jacketed, multiconductor assembly cord.

The circuit supply conductors in our SACB cables are 18 AWG. Our sensor actuator cables have 18 AWG
conductors. Cables to our push button panel have 18 AWG conductors.

13.6.4 Conductors for PLC I/O shall not be smaller than30 AWG if part of a jacketed, multiconductor assembly cord.
The I/O conductors in our SACB cables are 22AWG


14.1.2.1 Factory-applied connectors molded onto cables shall be permitted.
Our SACB master cable has a molded connector supplied by manufacturer.


14.1.3 Conductors of different circuits can be laid side by side and occupy the same cable, raceway or cable tray as long as this does not impair the function of the respective circuit.
Functionally associated circuit conductors including power, control, remote input/output, signaling and communication cables shall be permitted in the same wire way regardless of voltage, provided they are all insulated for the maximum voltage.

This rule allows us to run all cables together as long as each rated for 600 volts. We don?t of course.


14.1.4.1 Exposed cables installed along the structure of the equipment or system or in the chases of the machinery is allowed.



Cable trays

14.5.10 Cable trays are permitted to support conductors, cables or raceways.
(1) Sing conductors 1/0 or larger associated with machine
(2) Multiconductor cables that are otherwise permitted on industrial machines.
(3) Raceways functionally associated with industrial manufacturing systems.
All our motor cables are Type TC-ER. Our Class 2 and communication cables are Tray Rated (CL2, CM
and CM). Our SACB cable is the only cable that is NOT Type TC or TC-ER. Item (2) allows us to put
SACB cable in the tray.

 

[sunsys]

Re: Article 725

Nothing was mentioned regarding the AWM wires listed in "example #3" on Novemeber 19th.

Can AWM be used or not?

 

[grecon]

Re: Article 725

If the AWM cables you are refering to are the two Belden cables, then the answer is "yes"
I did not find an article in NFPA 79 that pertains just to communications but 14.1.3 lets you run power,signaling, communications etc all together.
14.1.4.2 and 14.1.4.2 allows cables to be exposed, suspended and supported along the machine.
The cable is tray rated.

 

[sunsys]

Re: Article 725

The article I'm thinking about where there could be a violation depending on the application is NEC 800.53(E)(1)-(3) and table 800.53

I'm thinking you're seeing the application in the example as OEM equipment and furnished raceways. But if the communication wiring leaves the equipment and is installed in building raceways, then I wouldn't think NFPA 79 applies, and the wires are limited to NEC article 800.

Those Belden cables are specified as NEC CL2, what about AWM communication wires that aren't NEC classified as CL2, or CM, such as flat moulded 4 wire phone cable pre-wired with RJ22 connectors at each end?

[ December 23, 2004, 04:59 PM: Message edited by: sunsys ]

 

[grecon]

Re: Article 725

NEC 800.53(E)(1)-(3) Table 800.53? I could not find in 2005 code book?

The equipment in question is OEM equipment.
Any cables that are NOT ON MACHINE or do not end up on the electrical equipment of the machine must apply NEC code not NFPA 79. (this is Chapter 1 of NFPA 79)

Have not taken the time to determine if the cables in question have to be in their own separate conduit. In the past we have always put CAT 5 cable in separate conduit.

If you find out let me know.

Thanks