Class 2 industrial photo-eye

[jomijen]

I have been researching the need for Class 2 wiring on our conveyor equipment. It seems that photo-eye and other device manufacturers are adding a "class 2" rating to the cables attached to their devices in order to get a UL listing. It has been our opinion that we need to provide class 2 power to these class 2 devices. This includes CanBus cabling used for communications on the equipment.

My questions:

As an industial equipment manufacturer, are we not bound by NFPA 79 as opposed to the requirements of the NEC article 725?

Does the fact that the device manufacturers class 2 listing on the cable trump the requirements of NFPA 79?

I feel that I am getting forced into Class 2 requirements per NEC 725 because of the devices, when our general wiring methods should be guided by NFPA 79.

 

[hbiss]

IMO within and on the equipment NFPA 79 applies. When wiring extends beyond the equipment, from one piece to another for example, NFPA 70 (NEC) would apply. As far as CL2 is concerned, I'm not familiar with NFPA 79 so I can't say if there is a CL2 equivalent for wiring but I don't think that matters beyond the physical equipment as far as the NEC is concerned. I believe what you are talking about is the equipment supplying power to devices or other equipment via wiring that extends beyond the equipment. Since that wiring falls under the NEC any power source in the equipment must be CL2 listed and the external cable or wiring must be at least CL2.

-Hal

 

[jomijen]

Thanks for the response Hal.

If the photo-eye with the class 2 rating is part of the equipment, as is it's power source (remote mounted disconnect box mounted to equipment), then this falls under NFPA 79 and I can ignore the CL2 requirement, even though the photo-eye is rated as CL2?

Thanks.

 

[petersonra]

I have no idea what your real question is. perhaps you could restate what your concern actually is. Is someone claiming there is a problem with an existing installation?

In any case, CANBUS (and its derivative DeviceNet) are both class 2 circuits, and have to be fed with class 2 power supplies. I am not aware of any requirement that devices attached to a class 2 circuit require any special listing in NFPA79 or any other standard that might apply to this type of equipment.

I am of the opinion that the wiring within a machine is not subject to the NEC anymore than the wiring inside your vacuum cleaner is.

The wiring between different parts of a machine is kind of iffy, but I am inclined to think it is not either, although there are no doubt a lot of people who think otherwise. If it is covered by the NEC, than the many, many machines that are wired together with factory supplied cords are probably in violation of the code.

At some point there has to be some common sense involved in these kind of things. Fortunately, most of the time this type of stuff is not inspected so it does not come up.

I don't see how having a cable that is listed as being suitable for class 2 circuits requires that it be used only in a class 2 circuit.

 

[jomijen]

Thanks petersonra -

This "research" started as I began looking into some cost savings on our equipment. Essentially, I am trying to understand the contradiction between CL2 requirements, and the use of NFPA 79 on industrial machinery.

1) All of the wiring I am referring to is "within the machine". This makes it an NFPA 79 application.
2) NFPA 79 does not reference CL2 installation guidelines in its standards.
3) NEC refers to CL2 methods for building wiring, and not machinery.
4) Why, then, do sensor and DeviceNet media manufacturers list thier devices as CL2 if they are primarily used on industrial machinery?

Scenario: I have a UL listed control cabinet that is physically attached to a machine. A DeviceNet cable with a CL2 rating runs along the machine frame and attaches to a node. Do I have to use a CL2 power source? Neither NEC 725 or NFPA 79 really answers that question as far as I can tell.

Thanks

 

[hbiss]

Why, then, do sensor and DeviceNet media manufacturers list thier devices as CL2 if they are primarily used on industrial machinery?

Because their devices are sold (or they want to sell) to other markets where they are not part of a piece of machinery. Not being NEC compliant would restrict their sales.

Scenario: I have a UL listed control cabinet that is physically attached to a machine. A DeviceNet cable with a CL2 rating runs along the machine frame and attaches to a node. Do I have to use a CL2 power source?

IMO no, as long as everything is within the machinery "boundaries".

-Hal

 

[petersonra]

Scenario: I have a UL listed control cabinet that is physically attached to a machine. A DeviceNet cable with a CL2 rating runs along the machine frame and attaches to a node. Do I have to use a CL2 power source?

IMO no, as long as everything is within the machinery "boundaries".

-Hal

I am inclined to agree as long as you are only referring to NEC requirements.

However, most of the manufacturers instructions refer to the NEC. One might conclude that as part of the manufacturer's instructions, whatever might apply that is in the NEC might be logically assumed as being required to list the control panel.

I also note that at least the 2005 version of NFPA79 only refers to class 2 circuits in passing by exempting them from ground detect lights if they are ungrounded. that would seem to imply that there is at least some recognition that class 2 circuits might exist within the boundaries of an NFPA79 covered application.

Note that in UL 508a, they define a class 2 circuit roughly the way the NEC does and seems to require that class 2 circuits meet special requirements, thus implying that there is at least some requirement to comply with class 2 issues. It is very poorly written though. The actual requirements are not real obvious.

 

[jomijen]

Thanks again for the responses.

I think the best method to ensure compliance with any AHJ is to use the CL2 source where the manufacturer of the device requires it. I do believe that UL and NFPA should collaborate on how these devices are applied on industrial machinery and come to some agreement on how they are listed. I don't necessarily agree that the same level of protection is necessary on machinery than it is in a building, but if that is the current code (as fuzzy as it is) then that is what we must design to.

 

[hbiss]

I think the best method to ensure compliance with any AHJ is to use the CL2 source where the manufacturer of the device requires it.

Well, I think you are putting the cart before the horse so to speak. According to the NEC it is the power source that dictates the wiring to be used, not the device (load). There is no such thing as a CL2 (or CL3 or Class1) load, only power sources. If you think about it, the loads can't be rated because if you parallel enough of them you will exceed the CL2 limits.

Of course, if the load (device) incorporates an integral CL2 listed cable for connection that pretty much limits what you can supply it's power with. However, if the device manufacturer just gives you a length of CL2 listed cable to be used with the device you are free to toss it and use whatever is appropriate for the VA of the supply. (Pretty much the way it is with LV puck lights.)

Then too, in practical terms, listed transformers and power supplies are readily and cheaply available. Use em and you won't have to worry about anything.

-Hal