Electrician Talk banner

16-212

444 Views 14 Replies 4 Participants Last post by  CAUSA
Can class one and class two wiring be in the same tech cable.
Example two pressure transmitters (class 2) and one 120 volt (class one) input
1 - 15 of 15 Posts

· Registered
Electrical Contractor
Joined
·
5,666 Posts
Can class one and class two wiring be in the same tech cable.
Example two pressure transmitters (class 2) and one 120 volt (class one) input
You found the code rule, don't like what you read?
 

· Electrical Contractor
Joined
·
5,995 Posts
Pressure transmitters are usually connected with shielded cable. I think a multi conductor cable would have too much interference.
 

· Registered
Electrical / Instrument journey man
Joined
·
111 Posts
Discussion Starter · #5 ·
Pressure transmitters are usually connected with shielded cable. I think a multi conductor cable would have too much interference.
For sure that is a risk i think I know what was confusing me was sub rule 5 but it is only when a remote device is used. I got it now.
When i get back to work I have to see if the other devices in the cable I’m looking at are suppled be a class 1 or class 2 power supply
 

· Registered
Electrical Contractor
Joined
·
5,666 Posts
I assume the other thread you started is the same installation. You said it worked fine for 20 years (your guess) until a single pair cable shorted.

Have I understood all that correctly?

How does a short on an input to a PLC wreck a camera?

You mentioned welding slag on the cable, I assume it was not a teck cable. Any chance the welding itself took out the camera?

If the 16pr cable appears good all you would need is a new run to the camera. I'm sure you are familiar with terminating the shields on that type of cable.
 
  • Like
Reactions: glen1971

· Registered
Electrical / Instrument journey man
Joined
·
111 Posts
Discussion Starter · #7 ·
I assume the other thread you started is the same installation. You said it worked fine for 20 years (your guess) until a single pair cable shorted.

Have I understood all that correctly?

How does a short on an input to a PLC wreck a camera?

You mentioned welding slag on the cable, I assume it was not a teck cable. Any chance the welding itself took out the camera?

If the 16pr cable appears good all you would need is a new run to the camera. I'm sure you are familiar with terminating the shields on that type of cable.
[/QUOTE

the single pair which came out of junction box with the 16 pair did a pretty good job of wrecking the camera.
The 16 pair cable which is probably 150 meters long had a 120 volt signal which came from the camera to the plc.
What I’m trying to do is fix the problem and do it right by the code book.

1.120 volt in the 16 pair fed from a 15 amp breaker wrong.
If put this on a 5 amp fuse that would be correct by code. I believe it would class 1 circuit.
2. Class 1 by code can’t be ran with class 2 wiring which I’m pretty sure a pressure transmitter and temp transmitter that is in the 16 pair cable would be class 2.
3. I have a question about the code if I put a 500
Milli amp fuse on the 120 volt circuit does that make it class 2 wiring now ?
 

· Registered
Electrical Contractor
Joined
·
5,666 Posts
the single pair which came out of junction box with the 16 pair did a pretty good job of wrecking the camera.
The 16 pair cable which is probably 150 meters long had a 120 volt signal which came from the camera to the plc.
That is the part I don't understand. The 120V came from the PLC to a contact on the camera. How does a short in this cable wreck the camera? A short would just indicate to the PLC the contact is closed all the time.

What am I missing here?
 

· Registered
Electrical / Instrument journey man
Joined
·
111 Posts
Discussion Starter · #9 ·
That is the part I don't understand. The 120V came from the PLC to a contact on the camera. How does a short in this cable wreck the camera? A short would just indicate to the PLC the contact is closed all the time.

What am I missing here?
I have explained it wrong 120 volt comes from the Breaker and feeds a plc and controls for a flare and ignitor.120 volt feeds the pic power and a terminal strip. Out of the terminal strip in a control tech cable is 120 volt white wire from there It goes to pcu cabinet and connects to the 16 pair control cable to the far building jb which then goes to single pair cable which goes to a contact on the camera which closes on no flame and sends a 120 volt input down the black wire to the plc.
the single pair cable failed. This is all done with #16 Control cable and is ran in a16 pair with other which I’m sure Is class 2 wiring. For what ever reason the short fried something in the camera I’m not worried about it’s a replacement with a new camera different style.

The 16 pair cable has class 2 and wiring it goes to transmitters. The 120 volt wire was off a 15 amp breaker a which is wrong. I would not put a 120 volt input in the 16 pair cable but it is.

1. if I put a 500 mili amp fuse on that 120 volt signal wire coming from the plc cabinet terminal strip
Would that make the signal a class 2 circuit because now it below 100va. Or am I thinking of the code rule wrong ?
 

· Registered
Electrical Contractor
Joined
·
5,666 Posts
Not sure what kind of PLC you are using but if anything, you should fuse your PLC. Then any 120V signal wiring would be protected also. Relocate the hot from the terminal strip to the PLC output.

Regardless of what is fused, a shorted signal wire to a PLC gives you a closed contact, or a ground fault, not damage to a camera downstream of the short.

The camera failure is likely coincidental.

Is it actually a camera or a flame sensor?

You can't fuse your way to a class 2 circuit. What if someone puts a bigger fuse in?

If the pressure transmitters, camera, and plc are all from the same source, you can certainly have all of that wiring in one cable as long as the cable has a voltage rating equal to at least the highest voltage utilized. I have used shielded pair cable for similar applications.

The following is just my opinion. If you have suspect cabling, replace it. If at this time you want to separate the different classes of wiring, go for it. But there really no reason to re-invent the wheel as I see it.
 

· Registered
Electrical / Instrument journey man
Joined
·
111 Posts
Discussion Starter · #11 ·
Not sure what kind of PLC you are using but if anything, you should fuse your PLC. Then any 120V signal wiring would be protected also. Relocate the hot from the terminal strip to the PLC output.

Regardless of what is fused, a shorted signal wire to a PLC gives you a closed contact, or a ground fault, not damage to a camera downstream of the short.

The camera failure is likely coincidental.

Is it actually a camera or a flame sensor?

You can't fuse your way to a class 2 circuit. What if someone puts a bigger fuse in?

If the pressure transmitters, camera, and plc are all from the same source, you can certainly have all of that wiring in one cable as long as the cable has a voltage rating equal to at least the highest voltage utilized. I have used shielded pair cable for similar applications.

The following is just my opinion. If you have suspect cabling, replace it. If at this time you want to separate the different classes of wiring, go for it. But there really no reason to re-invent the wheel as I see it.
you are correct on fixing it.Just trying to understand the code more your last answer helped a lot
Thx
 

· Registered
Electrical / Instrument journey man
Joined
·
111 Posts
Discussion Starter · #13 ·
One more question hopefully my last on this 16-212 1 (c) if class 2 and class 1 circuits were ran on the Same control cable each par has a metal sheath if I bond this to ground by code the same cable can have both classes of wiring even if they were from different sources ?
 

· Registered
Electrical Contractor
Joined
·
5,666 Posts
One more question hopefully my last on this 16-212 1 (c) if class 2 and class 1 circuits were ran on the Same control cable each par has a metal sheath if I bond this to ground by code the same cable can have both classes of wiring even if they were from different sources ?
My opinion again, shielding is not considered a raceway, grounded or not. So I say no.

But that is a reasonable question. Anyone else?
 

· Registered
Sub transient reactance X”d worshiper.
Joined
·
638 Posts
16-212 Separation of Class 2 circuits from other circuits 1) Insulated conductors and cables of Class 2 circuits shall be separated at least 50 mm from insulated conductors of electric lighting, power, or Class 1 circuits operating at 300 V or less, and at least 600 mm from insulated conductors of electric lighting, power, or Class 1 circuits operating at more than 300 V, unless effective separation is afforded by use of

a) metal raceways for the Class 2 circuits or for the electric lighting, power, or Class 1 circuits, subject to the metal raceway being bonded to ground;

b) metal-sheathed or armoured cable for the electric lighting, power, or Class 1 circuits, subject to the sheath or armour being bonded to ground;

c) non-metallic-sheathed cable for electric lighting, power, or Class 1 circuits operating at 300 V or less; or

d) non-metallic conduit, electrical non-metallic tubing, insulated tubing, or the equivalent, for electric lighting, power, or Class 1 circuits
 
1 - 15 of 15 Posts
Top