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Old October 29th, 2002, 09:41 AM   #1
TimothyMoulder
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Talking Color Code Application

So here's a little one for your consideration:

I have a 24 VDC system, with blue wire for +24 VDC and white-with-blue-stripe for 0 VDC

I have a sourcing input tied to a momentary pushbutton.

Wire-A goes from the input to one side of the PB

Wire-B goes from the other side of the PB to 0 VDC

Now the question : what colors should A and B be?

It may be argued that the input is a "24VDC Source), and A should be blue. Since B is tied to 0VDC, it should be white-blue

It may also be argued that the switch is transmitting 0VDC to the input, so both wires should be white-blue.

Finally, since this is a DC input circuit, there is an arguement that both wires should be blue, and white-blue should be reserved for dedicated power connections.

This one has me stumped. Any ideas?

TM
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Old October 29th, 2002, 09:51 AM   #2
Rick Densing
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A should be blue. B should be White/Blue, assuming your 0Vdc is grounded. B is always connected to ground, thus the white/blue. A could be 24VDC or 0. Go with the marking for the higher voltage. It could also be argued that since when A is brought down to 0V by the switch, it is not a "true" ground, being that is through a switch. The white indicates a grounded conductor, thus it cannot be white.
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Old October 29th, 2002, 11:09 AM   #3
rsdoran
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Personally I think if the 24vdc or any SOURCE/Reference voltage is using 2 specific colors those colors should NEVER be used to represent anything but SOURCE/Reference voltage.

I also prefer input wires to be a different color than output wires.

To me this makes the troubleshooting simpler, the maintenance/electrician will KNOW that the blue/white is a 0vdc reference to the blue 24vdc. IF a PB is being supplied by a blue/white then he knows that is a 0v reference and to check/verify can use the appropriate techniques. If you use the blue/white as an input wire from a PB then you lose reference points and it makes it more difficult to trace the circuit.

I go in cabinets daily that barely have more than all red or all black and it makes it slow to troubleshoot. The colors used do not matter that much (except for NPA and IEC conventions). WHAT does matter is that there is a method to the madness just like when writing code and documentation to explain.
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Old October 29th, 2002, 06:11 PM   #4
harryg
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NFPA 79 16.1.3 The use of other colors for the purpose of identification shall be as follows:
-BLACK: Ungrounded line,load,and control conducters at line voltage.

-RED: Ungrounded ac control conductors,at less than line voltage.

-BLUE: Ungrounded dc control conductors.

-YELLOW: Ungrounded control circuit conductors that may remain energized when the main disconnecting means is in the OFF position. These conductors shall be YELLOW throughout the entire circuit, including wiring in the control panel and the external field wiring.
NOTE: The international and European standards require the use of ORANGE for this purpose.

-WHITE or NATURAL GRAY: Grounded circuit conductor.

-WHITE WITH BLUE STRIPE: Grounded (current carrying) dc circuit conductors.

NOTE: The international and European standards require the use of the color LIGHT BLUE for the neutral conductor.

-WHITE WITH YELLOW STRIPE: grounded (current carrying) ac control circuit conductors that remain energized when the main disconnecting means is in the OFF position. For additional circuits powered from different sources that remain energized when the main disconnecting means is in the OFF position, striping colors other than GREEN, YELLOW or BLUE shall be used for the unique identification of the grounded conductors.
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Old October 29th, 2002, 08:28 PM   #5
Eric Nelson
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I agree with Rick (and Ron seems to be saying the same thing)...

Whatever color is designated as 0vDC should always reference 0vDC.

I use a "non-standard" (well, it's MY standard) color code for 24vDC supply conductors. DC+ (24vDC) is always orange, and DC- (0vDC) is always yellow. Yes, I know about the use of yellow (see Harry's post), but I don't care. I've been doing it this way for too many years to change now... moon2

I always use blue for switched DC (sinking or sourcing). Inputs OR outputs (sorry, Ron)

Heck, I might as well list MY "standard" color code (for what it's worth)...

BLK - AC conductors (ungrounded... AKA "Hot") that are not switched (other than by a circuit breaker)
WHT - AC conductors (grounded... AKA Neutral)
RED - AC conductors (ungrounded) that are switched
GRN - Ground conductors (though I'm using GRN/YEL as a standard now)
ORN - DC+ (unswitched)*
YEL - DC- (unswitched)
BLU - DC switched conductors
BRN - DC motor conductors (usually 90vDC in most cases)
VIO - Any "oddball" low voltage (a DC speed control "inhibit" circuit for example)
GRY - "Unknown" voltages (things like a dry-contact circuit for external signals when I don't know what voltage the customer might use)

*I do use orange on a "switched" circuit in one special case. To supply power to DC output card commons through an MCR, since it's essentially "unswitched" during normal operation. The same is true for "unswitched" AC conductors through an MCR. I use black for these.

beerchug

-Eric
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Old October 30th, 2002, 06:47 AM   #6
TimothyMoulder
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Request for Clarification

Ron :

>>Personally I think if the 24vdc or any SOURCE/Reference voltage is using 2 specific colors those colors should NEVER be used to represent anything but SOURCE/Reference voltage.<<

I gather from your post that neither A nor B should be blue or white-blue, but a separate color altogether for both? If so, would you use the same color or different ones?

Harry :

I'm trying to get a bit more standardized, thus the question The code seems to indicate blue-blue, but perhaps my interpretation is wrong.

Eric :

>>Whatever color is designated as 0vDC should always reference 0vDC. <<

Agreed, but perhaps I should clarify the question a bit.

The circuit is a sourcing input circuit. In the case of Wire B, is the wire considered part of the input circuit, or just a grounded neutral conductor? Look at it from the "input" side, it should be blue. Look at it from the "power-flow" side, the button is switching 0VDC, and both should be white-blue. Or is a compromise in order?

Which is the correct approach?

>>I use a "non-standard" (well, it's MY standard) color code for 24vDC supply conductors. DC+ (24vDC) is always orange, and DC- (0vDC) is always yellow. Yes, I know about the use of yellow (see Harry's post), but I don't care. I've been doing it this way for too many years to change now... <<

I think most people have their own special variations. My boss used to use orange for inputs and pink for outputs. I am introducing a few carefully-thought-out changes since he left, and one obvious one was to standardize the color code. Thus the question.

Thanks for the feedback!

TM
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Old October 30th, 2002, 07:12 AM   #7
Steve Etter
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Timothy,

In your original post, you wrote:

>>I have a sourcing input tied to a momentary pushbutton.

Wire-A goes from the input to one side of the PB

Wire-B goes from the other side of the PB to 0 VDC<<

As you describe your convention and several of the other posts that agree that the grounded conductor should always be the same color, I don't really see a delima: Wire A should be blue and and wire B should be white/blue.

Neither the fact that "the switch is transmitting 0VDC to the input" nor the observation that "this is a DC [PLC] input circuit" are relevent. The switched side of the circuit (wire A) MAY OR MAY NOT be at 0 VDC at any given time, therefore it acts the same as any other PLC input wire; at any random point in time you don't know for sure at what potential it will actually be. Wire B, on the other hand will ALWAYS be at 0 VDC and its color should indicate this.

Steve
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Old October 30th, 2002, 07:47 AM   #8
TimothyMoulder
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Steve :

That's what I was looking for. Thanks!

TM
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Old October 30th, 2002, 08:01 AM   #9
rsdoran
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Tim in this case Wire B goes from 0vdc to PB therefore it can be blue/white, at all times it will be a 0vdc reference point.

Wire A to me should be a different color that represents an input wire, inputs and outputs can be same color but to me it makes life a little easier if certain things are known. Example:
Black = 120vac hot
White = Neutral
Blue = +24vdc
Blue\white = 0vdc
Pink (or any specific color) is outputs
Purple (or any specific color) is outputs

Just makes troubleshooting/tracing ckts a little easier.
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Old October 30th, 2002, 08:29 AM   #10
Tom Jenkins
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I use a simple rule in deciding on which color to use for the wiring. If a conductor is ALWAYS at the same voltage as a referenced color, it should be that color. If the state is unknown or varies, use the color of the higher voltage.

In the original example, the second contact on the pushbutton is tied drectly to the "-" side of the power supply, so it's wire should be the same color as the wire on the "-" terminal of the power supply: in his case blue/white. The other contact may be at 24 VDC or it may be at 0 VDC depending on the state of the pushbutton. Therefore, it should be blue.

As an aside, in my opinion unless the "-" side is verified as tied to ground it should be blue, not blue/white. The wire number marker can be used to distinguish between "+" and "-" if both are blue.

Eric, there is nothing against code in your wire color standards. Unfortunately, maybe from the automotive industry, blue for DC is "almost" universal in the US. Do you put a sticker with your wire color code inside the panels to alert other electricians to yor standard?
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Old October 30th, 2002, 10:55 AM   #11
Eric Nelson
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Quote:
Originally posted by Tom Jenkins
Do you put a sticker with your wire color code inside the panels to alert other electricians to yor standard?
No, it's only on the electrical schematics legend, but that's a great idea! If the documentation gets "misplaced", at least there will be some reference permanently attached to the panel.

Any ideas on better (clearer) descriptions to use, rather than stuff like "unknown" and "oddball"?...

beerchug

-Eric
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Old October 30th, 2002, 12:35 PM   #12
Tom Jenkins
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Instead of "unknown" we identify voltages from outside our panel, such as power to a dry contact, as "foreign" voltage. I've seen this in specs and other company's drawings as well. We usually use yellow for this, even if I expect it to be 24 VDC, on the assumption that it is safer to assume a higher than actual voltage is present than the converse.

The "oddball" is not a usage we need often - perhaps "application specific" or "device generated" would sound better?
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Old October 30th, 2002, 04:17 PM   #13
Eric Nelson
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Thanks Tom, those sound much more professional!...

beerchug

-Eric
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