Class 1, 2, 3 circuitry; whats the difference?

[rhamblin]

I work in a printing plant. About a year ago, one of our presses had some wiring "upgraded". This was not overseen by an engineer.:happysad: Recently I was called out to find out why the plates weren't kicking in. This is done by energizing a 24V DC valve. There are 6 valves per module, and 9 modules on this press. I discovered the fuse holder was in bad shape and that it had a 20 amp fuse in it. But the wire running to and from the fuse holder was 16 AWG. So it should probably have a 10 amp fuse in it.

Well after burning through a 10 amp & 12 amp fuse I replaced it with a 15 Amp. Later, I put an amp clamp on it to find out that we are drawing 13.99 amps when the plates are kicked in (valves energized). My first thought was that I would have to re-pull larger wire throughout the 130' long press. And then through each of the 9 modules. :jawdrop: Not looking forward to that.

Looking for a simpler work around, I checked out 240.21, to see about increasing the horizontal line, that runs down the press. And tapping off of it and not increasing the size of the wire going through the modules. If I were to do this the distance from the tap to the final valve would be between 10-25'. So then I looked at 240.21(B)(2), however the final connection between the valve and the last junction box is run with SO cord. So this would seem to eliminate that option.

Then I thought, since this whole circuit is fed from a DC Power-supply, maybe it could be considered a Class 1, 2, or 3 circuit. So I grab my 2011 NEC code book (in WI we haven't upgraded yet to 2014), but I am not sure what dictates the difference between a Class 1, 2, or 3 circuit.

Any help/suggestions for a simpler work around on the press or explanations on the Class 1, 2, 3 circuitry would be much appreciated.

 

[iwire]

I may be mistaken but class 2 and class 3 have to be marked on the unit per the maker.

You can see the power limitations by going to Tables 11(A) and 11(B) in chapter 9 of the 2011 NEC.

 

[__dan]

Class 1 is regular power wiring using one or more of the wiring methods provided, listed, in chapter 3, the NEC 300's.

Class 2 or 3 is an article 725 wiring method for power limited building control wiring, allowing the more fragile wiring methods of art 725 (CL 2 cable) and exceptions from the requirements of chap 3. Class 2 is allowed provided the upstream power supply is a listed class 2 device. Power limits of class 2 supplies are very low, in the range of 40 to 80 va along with inherently self protected circuitry / design.

It sounds like the load you are trying to power may be above the limits of class 2 listed methods but it is something to examine.

SO cord may be acceptable provided it plug in and not be hardwired. If it were me and I saw SO cord I might be automatically thinking FMC or LFMC.

 

[__dan]

Looking for a simpler work around, I checked out 240.21, to see about increasing the horizontal line, that runs down the press. And tapping off of it and not increasing the size of the wire going through the modules. If I were to do this the distance from the tap to the final valve would be between 10-25'. So then I looked at 240.21(B)(2), however the final connection between the valve and the last junction box is run with SO cord. So this would seem to eliminate that option.

Instead of tapping a larger horizontal run, you may be able to split the load into multiple circuits to get the draw down to the rating of the on module wire, or for convenience of isolating power supplied to different sections / modules. So keeping the module wiring but repulling more circuits to a point where the taps would be. The added individual power circuits could then be monitored by the automation system for outages.

 

[hbiss]

I know you said it was replaced, but was that wiring the same as what was originally provided by the manufacturer? Is it part of the "machine"? If so it may not fall under the NEC.

-Hal

 

[jusme123]

http://ecmweb.com/content/understanding-nec-circuit-classifications

 

[rhamblin]

Class 1 is regular power wiring using one or more of the wiring methods provided, listed, in chapter 3, the NEC 300's.

Class 2 or 3 is an article 725 wiring method for power limited building control wiring, allowing the more fragile wiring methods of art 725 (CL 2 cable) and exceptions from the requirements of chap 3. Class 2 is allowed provided the upstream power supply is a listed class 2 device. Power limits of class 2 supplies are very low, in the range of 40 to 80 va along with inherently self protected circuitry / design.

It sounds like the load you are trying to power may be above the limits of class 2 listed methods but it is something to examine.

SO cord may be acceptable provided it plug in and not be hardwired. If it were me and I saw SO cord I might be automatically thinking FMC or LFMC.

Actually, part of the upgrade was to replace the short length of LFMC with a short piece of SO cord that is hardwired. But I'm not sure why you think SO hardwired is a bad thing.

 

[iwire]

I'm not sure why you think SO hardwired is a bad thing.

As a general rule SO is not a wiring method to NEC. It is more or less limited to things that have plugs, move, flex, etc or are temporary.

In my opinion your installation likely violates 400.7(B) & 400.8(1).

400.7 Uses Permitted.
(A) Uses. Flexible cords and cables shall be used only for
the following:

(1) Pendants

(2) Wiring of luminaires

(3) Connection of portable luminaires, portable and mobile
signs, or appliances

(4) Elevator cables

(5) Wiring of cranes and hoists

(6) Connection of utilization equipment to facilitate frequent
interchange

(7) Prevention of the transmission of noise or vibration

(8) Appliances where the fastening means and mechanical
connections are specifically designed to permit ready removal
for maintenance and repair, and the appliance is
intended or identified for flexible cord connection

(9) Connection of moving parts

(10) Where specifically permitted elsewhere in this Code

(B) Attachment Plugs. Where used as permitted in
400.7(A)(3), (A)(6), and (A)(8), each flexible cord shall
be equipped with an attachment plug and shall be energized
from a receptacle outlet or cord connector body.
Exception: As permitted in 368.56.

400.8 Uses Not Permitted. Unless specifically permitted
in 400.7, flexible cords and cables shall not be used for the
following:

(1) As a substitute for the fixed wiring of a structure

(2) Where run through holes in walls, structural ceilings,
suspended ceilings, dropped ceilings, or floors

(3) Where run through doorways, windows, or similar
openings

(4) Where attached to building surfaces
Exception to (4): Flexible cord and cable shall be permitted
to be attached to building surfaces in accordance with the
provisions of 368.56(B)

(5) Where concealed by walls, floors, or ceilings or located
above suspended or dropped ceilings

(6) Where installed in raceways, except as otherwise permitted
in this Code
(7) Where subject to physical damage

 

[rhamblin]

I know you said it was replaced, but was that wiring the same as what was originally provided by the manufacturer? Is it part of the "machine"? If so it may not fall under the NEC.

-Hal

Hmm, interesting thought. Actually our printers were designed in house by engineers that we no longer have (budget cuts), and assembled in house (mechanically and electrically). From what I understand, these printers only exist in our two plants. They were never manufactured and sold to others.

There isn't per se a manufacturer, or there is, and it's us.

It was part of the machine originally, yes. One of the reasons for the upgrade was to change this wiring from 120V AC to 24V DC.

Does this mean the original machine wiring does not fall under the NEC? hmy:

 

[rhamblin]

As a general rule SO is not a wiring method to NEC. It is more or less limited to things that have plugs, move, flex, etc or are temporary.

In my opinion your installation likely violates 400.7(B) & 400.8(1).

Aahh, I don't believe it does because the short piece of SO cord is mounted on the printer, and is used for "connection of moving parts" 400.7(A)(9). You see the as the valve operates, it sends compressed air to a piston, causing the piston to expand or contract, which in the process causes the whole assembly to move/rotate a little bit.

 

[sii]

What kind of solenoid valve pulls 14 amps?

 

[chris kennedy]

This is done by energizing a 24V DC valve. There are 6 valves per module, and 9 modules on this press.

.

 

[hbiss]

Hmm, interesting thought. Actually our printers were designed in house by engineers that we no longer have (budget cuts), and assembled in house (mechanically and electrically). From what I understand, these printers only exist in our two plants. They were never manufactured and sold to others.

There isn't per se a manufacturer, or there is, and it's us.

It was part of the machine originally, yes. One of the reasons for the upgrade was to change this wiring from 120V AC to 24V DC.

Does this mean the original machine wiring does not fall under the NEC? hmy:

Likely then the whole assembly wasn't UL listed as a factory manufactured machine might be. If the original manufacturer used 16/2 SO cord, the machine was inspected and listed as such so any repair that maintains the original design is fine. Still, I don't think that the NEC applies to the internal wiring of machinery anyway unless that wiring extends out into the premises. It's up to the engineers who built it to determine what is suitable.

-Hal

 

[packersparky]

Class 1 is regular power wiring using one or more of the wiring methods provided, listed, in chapter 3, the NEC 300's.

Class 1 wiring is not regular power wiring. See 725.41(A)&(B).

 

[sii]

Oh I thought he was saying ONE valve was pulling all that current, my bad.

 

[hbiss]

Class 1 wiring is not regular power wiring.

No it's not but whenever you see Class 1 you might as well treat it as power and light because it requires the same wiring methods.

-Hal

 

[Smart $]

... Still, I don't think that the NEC applies to the internal wiring of machinery anyway unless that wiring extends out into the premises. It's up to the engineers who built it to determine what is suitable.

-Hal

I agree... but the AHJ has the final say, i.e. the machinery is subject to AHJ approval. In most cases, the AHJ will adjudicate without examination provided there is EOR (Engineer of Record) documentation. If an examination is performed, the standard used will likely be NFPA 79.