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Electrical wiring color code standards

K

Ken S.

I understand that there are some differences with UL and NFPA 79. Generally we design the panels and have a UL shop manufacture them and label them. The question is whether BLUE wires shall be permitted to be used for ungrounded dc control conductors per 13.2.4.3 in NFPA 79, or whether ORANGE wire must be used per 13.2.4.1.

Note that the power supply within the control enclosure has a separate 120vac feed which allows the emergency stop functions to remain operable in the enclosure when the the main supply circuit disconnecting means is in the off position.
 
S

Steve Myres

I've used blue with an orange stripe for that scenario. Blue for voltage, orange for before-the-disconnect.

And, since the voltage is very low, the hazard intended to be communicated by the distinct color before the disconnect is low as well.
 
B

Bob Peterson

now you have changed your question from what UL508a says to what a different standard says.

I don't have a current copy of NFPA79, and in my 2002 version wire color codes are found in 14.2. In my version it is unclear what the requirement actually is for the specific question you ask.
 
D

Dr. G7

I know this is an old tread...nevertheless,
what is the bizarre history behind the standard industry practice of blue color wire for all +24VDC wiring in an industrial control panel (with the exception of a grounded 0 volt / negative) and then all wire is identified with wire number labels to help in troubleshooting down the road.

I am curious: circuits, sensors, & actuators wiring, blue is neutral, brown/black is +24DC. Do you know the reason/history of the switching around of the colors for panels? Also if all the wires are blue, I guess the only way to tell which wire is which is by wire labels and referring to a schematic?

why is
 
D

Dr. G7

I know this is an old tread...nevertheless,
what is the bizarre history behind the standard industry practice of blue color wire for all +24VDC wiring in an industrial control panel (with the exception of a grounded 0 volt / negative) and then all wire is identified with wire number labels to help in troubleshooting down the road.

I am curious: circuits, sensors, & actuators wiring, blue is neutral, brown/black is +24DC. Do you know the reason/history of the switching around of the colors for panels? Also if all the wires are blue, I guess the only way to tell which wire is which is by wire labels and referring to a schematic?
 
A

AMBIT AUTOMATION

Greetings from Ambit Automation
This is traditionally through a 250 Ohm resistor located somewhere in the return path. Recently 'Electrical' engineers and AC electricians have been trying to design and install according to what they know - AC, which is different from DC and also NOT found in most existing instrumentation installations.
nice discussion
 
D

Don Sigman

Dr. G7 said:
I know this is an old tread...nevertheless,
what is the bizarre history behind the standard industry practice of blue color wire for all +24VDC wiring in an industrial control panel (with the exception of a grounded 0 volt / negative) and then all wire is identified with wire number labels to help in troubleshooting down the road.

I am curious: circuits, sensors, & actuators wiring, blue is neutral, brown/black is +24DC. Do you know the reason/history of the switching around of the colors for panels? Also if all the wires are blue, I guess the only way to tell which wire is which is by wire labels and referring to a schematic?

why is
Click to expand...
The BRN/BLU is based on Asian and European wire colors.
 
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