Can Article 645 be used for Industrial Control Rooms with Raised Floor?

[jtinge]

To utilize the less restrictive wiring methods of Article 645, the six criteria listed in 645.4 of NEC 2011 have to be met. Three of those are the "room contains only listed IT equipment", "occupied by and accessible to, only those personnel needed for the maintenance and functional operation of the installed information technology equipment", and "only electrical equipment and wiring associated with the operation of the information technology room is installed in the room. Can an industrial control room having a raised floor be classified as IT room and utilize the Article 645 wiring methods if it contains industrial PLCs and other equipment in addition to listed IT equipment for control of processes or a plant and is accessible to operators of that of the non-listed equipment? It seems that many people classify these control rooms as IT rooms but the equipment and personnel accessible to that equipment don't meet the criteria of Article 645 that permits use of the less restrictive wiring methods. Is this correct? Can Article 645 be correctly utilized for industrial controls rooms as described above?

 

[pfalcon]

First off, don't let titles confuse the issue. For code purposes there is no such thing as an "Industrial Control Room".
The term "Industrial PLC (Programmable Logic Controller)" is a fancy term that under code is a piece of "Information Technology Equipment" with a special purpose.

Second, it doesn't matter what the IT equipment is controlling so the issue of "control of processes" or "the plant" are not relevant.

Third, most PLCs are listed for their purpose.

Fourth, it must be restricted to the operators of that equipment which does not restrict it to IT people.

Therefore the core concept of an "Industrial Control Room" does meet the base requirements for 645 EXCEPT

The portion of a PLC system that may violate the conditions of 645 is often called the Field Buss or I/O subsystem. A full cable field-buss such as DeviceNet, ControlNet, Ethernet/IP will probably still meet demands. Point-to-point I/O distribution will not. In short, all connections to the PLC must be "network" type connections. That also eliminates many useful PLC functions such as direct motor control through contactors or drives. Those are not permitted within the room.

 

[don_resqcapt19]

I don't see a PLC as being within the scope of Article 645. UL does not list PLCs as information technology equipment. PLCs are listed as industrial control equipment.

 

[pfalcon]

Paying too much attention to function and not category. PLCs are isolated from ITE under UL.

 

[don_resqcapt19]

Paying too much attention to function and not category. PLCs are isolated from ITE under UL.

The point is that Article 645 only applies to listed technology equipment. If the industrial control system is not listed as such you can't use the rules in Article 645. i agree that for practical purposes there is no real difference between some PLCs or other industrial controllers and information technology equipment, but there is a code difference and as it is now written you can't use the less restrictive wiring methods unless the equipment in the room is listed information technology equipment. 645.4(3).

 

[jtinge]

Thanks for the insight. I think I agree with Don that unless the PLC equipment, and other control equipment is listed IT equipment, one can't take advantage of Article 645 wiring methods. Anybody with design experience of control rooms with raised floors for say a process plant, chemical plant, refinery, windtunnel, etc? Do you treat these type control rooms as IT rooms under Article 645, assuming they meet the other criteria for disconnects, fire barriers, and HVAC?

 

[pfalcon]

Sorry, guess I was too brief with my reply to Don.

Initially I was paying too much attention to function. As Don stated, there is no real functional difference but...

Paying attention to category the UL says a PLC is "Industrial Control" under NIMX rather than one of the ITE categories that start NG--

So just as a rose by any other name is tax deductible ... ITE by any other name no longer qualifies for 645. Another one of those idiotsynchrases (sic) where function is overwhelmed by bureaucracy.

Out of curiousity. Where in the wiring system did someone think there were

less restrictive wiring methods of Article 645

I see no advantages.

 

[don_resqcapt19]

The wiring under the raised floor in an Article 645 application is not that same as what would be required in other locations. For example 645.5(D) permits cords below the raised floor, but in other applications those cords would be a violation of 400.8.

 

[iwire]

Out of curiousity. Where in the wiring system did someone think there were

I see no advantages.

If it was not for the less restrictive wiring methods allowed by 645 there would never be any reason at all to use 645 at all. The NEC does not require the use of 645 it only allows it.

 

[jtinge]

I agree that Article 645 permits a less restrictive wiring method if all the criteria is true. The quandry I have is that some of my customers want to use the Article 645 methods, like not having to use plenum rated wire in the below raised floor area, when the equipment in the control room don't satisfy the Article 645 requirements. I believe that the use of the PLC's and other control equipment in the control room prevents being able to take advantage of the Article 645 wiring methods.

 

[pfalcon]

The wiring under the raised floor in an Article 645 application is not that same as what would be required in other locations. For example 645.5(D) permits cords below the raised floor, but in other applications those cords would be a violation of 400.8.

PLCs don't have the massive number of cables present for IT equipment. A raised floor for industrial control would be more expensive than the conduit, better cables, and raceways. Add the self-contained air system 645.4(2), etc that are required by 645 and I sincerely doubt the cabling balances the expense. The special walls and doors required 645.4(5) will eat up any savings. There's far more expense in 645 requirements than savings from cheap cables.

I agree that Article 645 permits a less restrictive wiring method if all the criteria is true. The quandry I have is that some of my customers want to use the Article 645 methods, like not having to use plenum rated wire in the below raised floor area, when the equipment in the control room don't satisfy the Article 645 requirements. I believe that the use of the PLC's and other control equipment in the control room prevents being able to take advantage of the Article 645 wiring methods.

As posted earlier, first by Don, the PLC and its chassis will be UL listed as NIMX industrial control but not NG-- information technology equipment. Therefore a room with a PLC cannot follow 645.4(3)