24VDC Control level wire colors.... whatever I want? 1

[FreddyZ]

Central USA...

4-circuit control panel for in-house testing, to run timered tests of 240V single phase items up to 2HP...

It's OK to use red for (+) and green for (-) on the 24VDC which runs the timer, current sensors, etc., right?

As it is in-house and not for others, I can use any color that's handy, right? Never mind that green is usually a ground color. The wires are small, like #24 AWG, so there should be no confusing a control level green with a 240V much larger diameter ground.

Thanks!

 

[djs]

We usually use blue for +24VDC and gray for 0VDC

 

[controlnovice]

Green can be used if:

NEC Article 250.119 says green cannot be used for un-grounded conductors with the Exception: Power-limited Class 2 or Class 3 cables, power-limited fire alarm cables, or communications cables containing only circuits operating at less than 50 volts where connected to equipment not required to be grounded in accordance with 250.112(I) shall be permitted to use a conductor with green insulation or green with one or more yellow strips for other than equipment grounding purposes.

Limited energy circuits are not required to be grounded (double check NEC)

Double check your class of system to know if you can do it.

NEC 400.23 says green shall not be used for other than grounding conductors.

Even with this, I would not use green in my plant for a current carrying conductor. The Electricians would kill you.

______________________________________________________________________________
This is normally the space where people post something insightful.

 

[FreddyNurk]

No way would I want to run red and green for +24V DC, as controlnovice mentioned its expected to be the ground wire so isn't really a good idea. I'd also avoid any colours that can be arbitrarily confused by people with less than adequate colour identification abilities, using red and green together in such a manner would certainly be one of those cases.

I've seen grey and brown used for 24V DC, I've seen orange and brown used for 24V DC, and I've also used orange and grey for 24V DC, the last one largely due to concerns about confusing colours with phase colours.

If possible, I'd also review the other wire colours likely to be used in the equipment and avoid them if possible, although that's not always easy to do.

As for the size issue, I've never seen an application where the expectation that 240V stuff is bigger and therefore not 24V DC or ground would hold. I still wouldn't do it even if you're using 0.5mm2 cable only for DC.

 

[MikeHalloran]

I'd definitely not use green, as noted above, nor red, for similar reasons.

Before our guvvamint forced manufacturers to go crazy removing weight from cars, you wouldn't find a wire smaller than 18AWG anywhere on an automobile, just because the smaller sizes are too delicate, as in easy to break just while cinching up the ty-raps. Try to strip some 24AWG wire with a pocketknife, and you'll find another reason to avoid it.





Mike Halloran
Pembroke Pines, FL, USA

 

[eeprom]

NFPA 79 has color standards for control panels: DC is blue and DC common is white with blue stripe.

But I wouldn't use green because most likely you don't want to ground your DC system, and having a green wire will imply that this is ground, as opposed to DC common.

EE

 

[FreddyZ]

OK, thank you folks very much.

Technically, it was not I performing this wiring but a co-worker.
It seemed not quite kosher to me, to use green for not-a-ground, and I wanted unbiased input.

I would rather use a different color, so if I am charged with the task, I will try to go that route. Blue and white sounds great to me.

 

[controlsdude]

example: Have this manufacturer of encoders 24vdc that have a green wire for an encoder direction bit. Every installation I have the electricians always associate green = ground. Try to follow the green = ground rule save you a lot of headaches.

 

[MatthewL]

MikeHalloran,

I worked for 10 years in the telecomm industry as an installer and splicer. I always used my fingernails to strip insulation from 24 and 26 AWG solid core to prevent nicking the core. Also, we would regularly tug on the wire once attached to the terminal to make sure there wasn't a nick on the copper that was covered by the stretched insulation. Those Ideal T-Strippers were notorious for marking the copper and causing an open fault, and were a pain to find.

Matt

Quality, quantity, cost. Pick two.

 

[MikeHalloran]

I love the Ideal strippers, for wire larger than ~24 gage.
It took me a while to figure out the trick of squeezing them all the way, so they would stay open briefly instead of kinking the wire.



Mike Halloran
Pembroke Pines, FL, USA