24 vdc color code

[nappuc]

I am in the process of installing several new process lines and corresponding MCC's with 24vdc plc control circuits. My company built the cabinets and used blue wire as the +24v line and white/blue as the 24v common wire. Electricians that build 100's of UL listed control cabinets are doing the electric work for us and they say white/blue is not legal as per the NEC and it should be a blue/white wire. In fact, they've never seen control circuits with white/blue wires. I inspected existing cabinets from other manufactures and they also use the blue/white and not the white/blue wire.

To verify which is correct, I searched the NEC and it clearly states 24v dc grounded conductors are to use the white/blue color code. I need to know which is correct. If we're wrong, we need to change our wiring practices.

 

[james wuebker]

Re: 24 vdc color code

nappuc
I'll try to find it in the morning. We have tons of machines with 24vdc wiring. They used blue for the 24v+ and purple for the 0v or what you called the common. The newer machines have changed and I'll check it out in the morning. I'll even call the machine company to find out what book they go by on the color code.
Jim

 

[jim dungar]

Re: 24 vdc color code

Per NFPA79 and UL508A, the suggested (but not required) color code for 24VDC grounded conductors is white with a blue stripe.

 

[dereckbc]

Re: 24 vdc color code

nappuc, I do not design 24 VDC control for PLC, but tons of design for 24 and 48 VDC power used in telephone offices. From my experience there is absolutely no code requirement for any type of color code Each industry has there own voluntary practices, but no regulatory requirements.

I have used every color scheme you can think of. my favorite is black for both battery and return. I use heat shrink labels/tags to identify origination and destination.

 

[james wuebker]

Re: 24 vdc color code

nappus
Blue is used for 24vdc+ and white with a blue stripe is used for - or 0 volts. Still haven't found what book they use to go by but NEC doesn't have it in theirs.
Jim

 

[petersonra]

Re: 24 vdc color code

Mostly we use blue with a white stripe or blue with a white band of tape on each end, because many of our panels are built to spec.

I think the trend is towards white with a blue stripe though.

NFPA79 extract

14.2.3.2 The use of other colors for the following applications shall be as follows:
(1) WHITE with BLUE stripe for grounded (current carrying)dc circuit conductor.

It appears this is not a suggestion, but rather a requirement if your panel is covered under NFPA79.

 

[LarryFine]

Re: 24 vdc color code

Is there any rule that defines what percentage of a conductor's circumference a stripe cannot exceed? In other words, what if it just happens to be a really wide stripe?

 

[nappuc]

Re: 24 vdc color code

I did a bit more digging today. i'm not sure but the blue/white wire may be a UL 508a code requirement. I do not have the UL code book, so I'm still not sure.

 

[jim dungar]

Re: 24 vdc color code

UL508A is not a code, it is a standard. For most items built under UL508A 24VDC color codes are not specified. There is only one specific section in the standard that does require the white with blue stripe. However UL508A does suggest NFPA79 which also suggests white with a blue stripe.

I would have a problem calling anything over 50% coverage a "stripe".