We are in a debate here, any information would be helpfull. Are there industry recommended standards for wiring PLC's. Ex. analog input would be xyz color and and digital input would be abc color
For Industrial Machinery in USA wiring color code is dictated by NFPA 79 "Electrical Standard for Industrial Machinery". In Europe it is EN 60204-1. Most if not all end users will hold machinery builders to one and/or both of these standards.
NFPA79 has some guidelines for some of these questions. I don't believe it encourages different colors for different types of PLC inputs, but rather by voltage and whether the conductor is grounded or not. Normally red is used for 120VAC I/O and blue for 24VDC I/O (the most commonly seen I/O voltages). Analog I/O generally uses some kind of shielded cable.
In a technical sense this standard only applies to machine tools (read the preface if you don't believe this). I believe there is another standard that applies to plastic machines. I don't believe there is a standard that applies specifically to the process industries (chemical, refinery, etc.). There may be an IEEE or ISA standard that could apply.
Interestingly, an issue arose today with a client. The question was raised as to whether it was "legal" to put solenoid valves inside control panels. NFPA79 prohibits this practice, but since they are not making machine tools NFPA79 really does not apply. I am not a huge fan of putting solenoid valves inside control panels for the obvious reasons, but cannot find an absolute
prohibition against it that actually applies in their case.
Bob Peterson
On December 11, 2002 11:30 am, Bob Peterson wrote:
<clip>
> Interestingly, an issue arose today with a client. The question was
> raised as to whether it was "legal" to put solenoid valves inside
> control panels. NFPA79 prohibits this practice, but since they are not
> making machine tools NFPA79 really does not apply. I am not a huge fan
> of putting solenoid valves inside control panels for the obvious
> reasons, but cannot find an absolute prohibition against it that
> actually applies in their case.
<clip>
I'm not sure how the various laws and regulations are applied in the United States. However under the health and safety acts for industrial establishments here if there is a situation which does not have a standard which applies directly to it you are expected to find a suitable standard somewhere which could reasonably be applied.
In other words if there was a standard which applied to machine tools but no comparable standard which applied to the exact type of equipment I was working on, I would need to have a very good reason to show why the machine tool standard was *not* suitable for the application before I simply ignored it.
Your feelings with regards to the solenoid valves are probably correct. The question should be though whether the reasons for prohibiting control valves in machine tool control panels are also valid for the type of machinery you are dealing with.
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Michael Griffin
London, Ont. Canada
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In their case its very convenient to put a stack of pneumatic valves into a small local PLC panel so its all in one box. It seems sort of silly to add an extra jbox on a skid to enclose the solenoid valve stack. One of my big objections is allowing the air to exhaust inside the control enclosure, which leads to oil collecting inside the enclosure. They actually run a vent line to the outside of the box.
These things are not machines at all (water treatment vessels) so the usual thinking about why things are done in the machine tool world just don't apply.
Bob Peterson
Bob,
Something I ran into a number of years ago (and you likely have considered this for your electrical cabinet): On a positioning machine the exhaust was expelled into a frame member (to avoid air disturbances near the operator). Some time later a consciences millwright plugged a hole that was "leaking some oil" on the far side. The square tube frame became pressurized and with might expelled the plug...lucky no one was in the way.
Hugo
The exhaust ports are tubed to the outside of the enclosure and a mud dauber fitting installed. It seems unlikely anyone would plug such a port. And if they did, it would become immediately apparent as the equipment would fail to operate.
Bob Peterson
I've never seen this done anywhere else (although I have seen valves inside their own box). One point you may want to investigate though is that some types of valves have a separate exhaust for pilot air. This extra exhaust port is not always very obvious or well documented by the valve manufacturer. They often don't put a muffler on this port, so it is sometimes just a small hole at the bottom of the manifold.
> These things are not machines at all (water treatment vessels) so the
> usual thinking about why things are done in the machine tool world just
> don't apply.
<clip>
I assumed the prohibition had something to do with the oil presenting a fire hazard, or causing damage to insulation or electrical component materials. There is also often water in the air, sometimes quite a bit if there are
problems with the compressor or the air piping is not installed correctly. This could present a potential electric short or shock hazard if there was a leak.
Another point to consider is that the tradesmen who service the pneumatics are not generally electricians, and do not work inside electrical enclosures.
I don't know your project very well, so I can't reasonably offer an opinion on it. However, while the location of the valves seems to be an issue, what about the FRL, dump valve, and pneumatic lock out? If the condensate bowl is
inside the enclosure too, how does it get emptied (or checked)?
I'm sure that all this has been thought of in your situation, but these sort of problems are probably why we don't often see pneumatics inside electrical enclosures.
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Michael Griffin
London, Ont. Canada
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> > In their case its very convenient to put a stack of pneumatic valves
> > into a small local PLC panel so its all in one box. It seems sort of
> > silly to add an extra jbox on a skid to enclose the solenoid valve
> > stack. One of my big objections is allowing the air to exhaust inside
> > the control enclosure, which leads to oil collecting inside the
> > enclosure. They actually run a vent line to the outside of the box.
>
> I've never seen this done anywhere else (although I have seen valves inside
> their own box). One point you may want to investigate though is that
> some types of valves have a separate exhaust for pilot air. This extra
> exhaust port is not always very obvious or well documented by the valve
> manufacturer. They often don't put a muffler on this port, so it is
> sometimes just a small hole at the bottom of the manifold.
As far as I know, the valves used do not have pilot air. The valve is directly actuated by the solenoid (through a spring). I have not seen any
buildup of oil or water in these cabinets over many years of service, except in cases where they are left open in dirty environments.
>
> > These things are not machines at all (water treatment vessels) so the
> > usual thinking about why things are done in the machine tool world
> > just don't apply.
> <clip>
>
> I assumed the prohibition had something to do with the oil presenting a
> fire
> hazard, or causing damage to insulation or electrical component
> materials. There is also often water in the air, sometimes quite a bit
> if there are problems with the compressor or the air piping is not
> installed correctly. This could present a potential electric short or
> shock hazard if there was a leak.
A good reason not to allow the valves to exhaust inside a cabinet.
> Another point to consider is that the tradesmen who service the
> pneumatics are not generally electricians, and do not work inside
> electrical enclosures.
Most places here in the US, either the instrument tech or electrician would service these small valves. They have no issues with working inside
electrical cabinets.
> I don't know your project very well, so I can't reasonably offer an opinion
> on it. However, while the location of the valves seems to be an issue,
> what about the FRL, dump valve, and pneumatic lock out? If the
> condensate bowl is inside the enclosure too, how does it get emptied (or
> checked)?
The FRL is located on the outside of the enclosure. Generally, the pneumatic lockout, is supplied by the end user, and would be external to the enclosure and would supply a group of these vessels, rather than a single vessel. Sometimes a ball valve is used to isolate the air supply to each vessel. This would also be on the outside of the enclosure, in front of the FRL (but we never use a lubricator!).
> I'm sure that all this has been thought of in your situation, but these sort
> of problems are probably why we don't often see pneumatics inside
> electrical enclosures.
Bob Peterson
In Europe control panels I have seen this standard.
1. Power - Black
2. Neutral - Light blue
3. Protection - green-yellow
4. Control volts 220V Ac-Red
5. Control Volts 24V AC-Red
6. Control Volts 24 V DC- dark blue
7. Analog Input - White
8. Analog output - Violet
9. Digital Input - Brown
10.Digital Output - Grey
11.External voltage(dry contact signals)-orange
11.Ex -i/d -blue (separated)
Also the terminal blocks are to be grouped as follows.
1. Power - X1
2. Protection - ground bus The ground bus is insulated from the panel back plate and back plate separately earthed to the busbar.
3. Control volts 220V Ac-X2
4. Control Volts 24V AC- X2
5. Control Volts 24 V DC-X3
6. Digital Input - X41
7. Digital Output - X42
8. Analog Input - X43
9. Analog output - X44
10.External voltage (dry contact outputs)- X5
11.Ex -i/d - X6 (separated)
Hope this helps
Regards.
Sekar
Hi Sekar,
I notice from your list that you use three different varieties of blue, with one reserved for "Ex i/d".
Note that IEC codes require that circuits protected under IS rules need to be specifically identified. Although it is not specifically stated in the code, this is conventionally done using blue coloured terminals, cables, etc. If you have IS circuits, it would be wise to restrict blue cores to those parts of the circuit protected by a barrier or isolator.
Bruce
In Canada we have the CSA Electrical code which is very much like the NEC code in the US. The CSA code states the following:
grounding or bonding: green or green with yellow
1 phase AC or DC (2 wire): 1 red 1 black or 1 black and 1 white
1 phase AC or DC (3 wire): 1 red, 1 black, 1 white
3 phase AC:
phase A red
phase B black
phase C blue
and 1 white (where neutral is required)
This is regardless of voltage.
We have to use these codes for field devices. We supply panels for many industries and countries, in-panel wire color codes vary widely and no standard seems to exist across all industries and all countries. In other words use anything but green (always used for grounding or bonding).
Allen Bradley offers a manual on THEIR recommended guidelines- and it's been pretty useful for our group. You can locate the manual in .pdf format by searching for the file: 1770-in041 a-en-p.pdf.
Hope this helps!
> ..... 1770-in041 a-en-p.pdf.....>
Has anyone been able to find this file at A-B or anywhere on the web?
You are right, this link to a standard Allen-Bradley document is a little
hard to find! Try:
http://www.ab.com/manuals/gi/1770-in041a-en-p.pdf
Hope this helps!
Larry Lawver
Rexel / Central Florida
Refer to the ISA standards publications. There is a lot of useful information in there, including the recommended practices for wire color codes. (Note that ISA standards are written in conjunction with the other standards organizations.)
Go to http://www.theautomationbookstore.com/public.html >item search > item
number 1770-4.1
Regards
Peter Green
on 
