Control Circuit - Opinion Needed

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Wattman

Member
To me the most non-compliant circuit I have ever seen, what do you think?:eek:

The project is an upgrade of the control system for some industrial existing equipment, basically the existing 1995 control panels were copied and the PLC system dated to a
Control Logix platform. It is my understanding that the system is for equipment safety, all of the CR's pertain to safety, this is a pressure vessel application.

Example "B" (new control panels contain this circuit)
I opposed this circuit for changes for several reasons
1st - a safety system must be done with Safety rated components relay, module, etc. (may have been OK in the 90's but not today)
2nd - the colors are wrong white can not be used as shown, would confuse electricians when troubleshooting
3rd - circuit does not comply with UL508A 45.
4th - I would have to check NFPA70 there has to be something in there, to prevent this.

I proposed at least a color code change of Example A

I was overruled and told these were "Safety Buss" circuits, we have always done it this way!

To me the most non-compliant circuit I have ever seen, what do you think?


Example1.jpg
 

Aleman

Senior Member
Location
Southern Ca, USA
Without seeing the rest of the schematic it's hard to say as far as safety compliance.

If all the relays are closed then all the white wires will be at N potential. The only line connection is on the output side of the relay.
Since these wires will never be above N then white is correct. My bet is that most guys would wire as shown on the A diagram. If
a tech couldn't figure out this out with a drawing in hand then they shouldn't be working on it to begin with. Unless you plan on
getting this listed then no worries.

And no I have seen a lot worse :)
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
A few comments.

I think it can be argued that either color code is OK.

I don't like opening the N side, both a NEC and UL508a violation.

I don't see how UL508a can be made to apply unless it is listed.

Often what are called safety circuits aren't.

Whether the circuit as shown is appropriate as a safety circuit or not depends entirely on the hazard analysis. What does it say?
 

Aleman

Senior Member
Location
Southern Ca, USA
Forgot to point out that the way this is wired is pretty screwy. All the relay contacts should be on the line side of the SV.
Then it would look normal.
 

Wattman

Member
Thanks for your input Mr. Perersonra

A few comments.

I think it can be argued that either color code is OK.
(I would argue at least Red, No switching can be done in the Neutral which is designated white, if circuit was 230VAC yea different story)

I don't like opening the N side, both a NEC and UL508a violation.
(I Agree)

I don't see how UL508a can be made to apply unless it is listed.
(I don't see how it does not apply, in theory all control panel are suppose to be UL listed as per NFPA70, maybe it gets a sticker, maybe not, but should try to comply.
not to mention NFPA79)

Often what are called safety circuits aren't.
(Good point - they use the term Safety Buss as if, it was a very common term to use, 25 years in the controls world and I have never heard it)


"Whether the circuit as shown is appropriate as a safety circuit or not depends entirely on the hazard analysis. What does it say?"

Yea this question could muddy the water more:
Yea in the USA end customer is suppose to take care of the "Risk Assessment" and specify their requirement
End Customer is likely a start-up company who purchased some used equipment, or one who has had the equipment since it was new, has no idea of a "Risk Assessment"
Send me a quote how cheap and how fast can I get it, type project.

The original OEM no longer exist.
I think any liability would fall to the end customer and the supplier of this new control panel.


----------------------------------------------------------------------------------------------------------------------------------------------------------------------
Thanks for your input Mr. Aleman

QUOTE=Aleman;1701628]Without seeing the rest of the schematic it's hard to say as far as safety compliance.

(There is not really much else to see, basically the CR's are driven by field devices, looking for pressures, and certain valves to be open or closed)

If all the relays are closed then all the white wires will be at N potential. The only line connection is on the output side of the relay.
Since these wires will never be above N then white is correct. (I think you are assuming they are all always closed, I have to lean toward never do any switching in the neutral)

My bet is that most guys would wire as shown on the A diagram. If a tech couldn't figure out this out with a drawing in hand then they shouldn't be working on it to begin with. Unless you plan on getting this listed then no worries. (I feel it can not be listed)
[/QUOTE]
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
The panel is either listed or not. Just meeting the standard is not remotely equivalent to being listed.

Nowhere in the NEC or nfpa79 does it require a control panel be listed.
 

Wattman

Member
The panel is either listed or not. Just meeting the standard is not remotely equivalent to being listed.

Nowhere in the NEC or nfpa79 does it require a control panel be listed.

I believe the answer is far more complex than you have stated:

Let me clarify all industrial control panels are required to be built to a UL508A and


NFPA 70 Section 409 the table 409.3
Meaning these articles are part of the code as well as UL508 and 508A soon to be replace in 2017 by UL 60947-4-1 specifications.

It is my understanding industrial control panel shall be UL labeled and built by Panel Builder with an UL 508A license
A UL 508A panel should be marked "industrial control panel" with the UL logo.
 

jap

Senior Member
Occupation
Electrician
From an overly simplistic person, to me, it would make more sense if the contacts were ahead of the load not behind it , but, if I was troubleshooting this and it was wired this way it would make more sense to me if it was wired per Example B where the Neutral "White Color" starts immediately at the load side of the solenoid.

The Red on the load side of the solenoid is confusing to me but thats JMHO.


JAP>
 

Smart $

Esteemed Member
Location
Ohio
How it should be done... IMO.

safety%20circuit.gif
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I believe the answer is far more complex than you have stated:

Let me clarify all industrial control panels are required to be built to a UL508A and

Nowhere in the NEC or NFPA79 is this ever made a requirement.

NFPA 70 Section 409 the table 409.3
Meaning these articles are part of the code as well as UL508 and 508A soon to be replace in 2017 by UL 60947-4-1 specifications.

Yes, and if you look at UL508a, the requirements from these sections are there, although not by reference as you are suggesting.


It is my understanding industrial control panel shall be UL labeled and built by Panel Builder with an UL 508A license
A UL 508A panel should be marked "industrial control panel" with the UL logo.

Yes, a UL508a listed control panel would have a listing sticker on it. It does not have to be from UL though. Other testing labs will list a product to the UL508a standard. We use UL for that purpose but I know there is at least one other company that lists control panels to the UL508a standard.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
How it should be done... IMO.

safety%20circuit.gif

it improves the wiring issues.

It would not surprise me if this was an attempt to protect the machine from people who change the PLC program without understanding the program or the machine very well. In that case it is not a safety circuit at all.

I used to see a lot of this kind of stuff that was tacked on after the fact by OEMs to protect themselves from plant people that like to fiddle with the PLC program. These days the OEMs just tell the owner that if the plant electrician fiddles with the PLC program the warranty is void, or they make it hard to change the PLC program by password protecting some or all of it.
 

Wattman

Member
Yes, a UL508a listed control panel would have a listing sticker on it. It does not have to be from UL though. Other testing labs will list a product to the UL508a standard. We use UL for that purpose but I know there is at least one other company that lists control panels to the UL508a standard.


Yes the UL508A stickers come from UL. we have an UL agent that comes to the office and checks our books.
 

Aleman

Senior Member
Location
Southern Ca, USA
Yes, a UL508a listed control panel would have a listing sticker on it. It does not have to be from UL though. Other testing labs will list a product to the UL508a standard. We use UL for that purpose but I know there is at least one other company that lists control panels to the UL508a standard.

TUV SUD can do UL508A listing.
 

kwired

Electron manager
Location
NE Nebraska
it improves the wiring issues.

It would not surprise me if this was an attempt to protect the machine from people who change the PLC program without understanding the program or the machine very well. In that case it is not a safety circuit at all.

I used to see a lot of this kind of stuff that was tacked on after the fact by OEMs to protect themselves from plant people that like to fiddle with the PLC program. These days the OEMs just tell the owner that if the plant electrician fiddles with the PLC program the warranty is void, or they make it hard to change the PLC program by password protecting some or all of it.
Rules and regulations aside, you can't idiot proof it, if you do eventually an improved idiot will come along.

If they are capable of changing the program, they are probably capable of modifying relay configurations as well.


Why can't these relays be internal to the program in the first place?


Next question for OP is what is operating voltage? If this is say a 24 volt class 2 circuit I see a lot less wrong with it then if it is a 120 volt circuit, just from NEC requirements perspective.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Rules and regulations aside, you can't idiot proof it, if you do eventually an improved idiot will come along.

If they are capable of changing the program, they are probably capable of modifying relay configurations as well.


Why can't these relays be internal to the program in the first place?


Next question for OP is what is operating voltage? If this is say a 24 volt class 2 circuit I see a lot less wrong with it then if it is a 120 volt circuit, just from NEC requirements perspective.
I think trying to outthink the idiots is a lost cause. Just tell the owner it is their problem if people modify the thing in any way. That usually reduces the fiddling around, or at least makes them understand.

The reason a lot of this kind of stuff was tacked on like this was because it is a lot easier to tickle the keys than it is to rewire stuff. It would not surprise me if the same interlocks are found in the code but are repeated externally in case someone gets the bright idea to improve something by fiddling with the code.

If it was a 24VDC circuit it is unlikely the OP would have referred to the power lines as L and N.
 
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