Hi Guys,
Been ages since I've started a new thread in this area, but I have a question for our Aussie and NZ folks.
I do a lot of work on dairy systems, where they use a 24 Volt control system to power the coils in contactors and what-not.
With some of these systems, you get a box that comes pre-wired and you merely hook the field wiring up to it, that's all well and good.
But, is there a standard that tells us all what wire colours are positive and negative when using the output side of a 24VDC SMPS in a box?
I've seen pink used as the negative, I've also seen orange as the negative, with violet being the positive most times.
Pretty much is seems like it is at the whim of the person that wired the enclosure, this is the reason why I ask if there is actually a standard to be referred to for this sort of thing?

On this side of the world I have seen all sorts of different colors used for low voltage and I do not think there is a standard.
Red hot and black common is used a lot. Then the next box over might use white for the hot and black for the common. That is exactly the opposite of what the mains voltage will be.
It seems low voltage engineers don't ever talk to mains voltage engineers.
Once you get past 2 colors, anything goes for the rest.
The only thing that you can usually count on is green with the yellow stripe is <earth> ground ... unless it is a car or a boat.

I have noticed (here in UK) that there seem to be numerous "conventions" observed peculiar to specific areas of technology. For example alarm engineers always seem to use the same colours for trigger and tamper circuits; Telephone engineers always use the same colours for line and ringing circuits. If you open up your PCs, the power unit wires seem to correspond between manufacturers, Vehicle wiring seems to have at least some consistency, USB cables seem the same, etc. I don't know where these "standards" originate, but they certainly do exist.

True, yet there were several power supply manufacturers that deviated from the usual black/red/yellow for computer 5 and 12 V wiring. I've seen orange instead of either red (Amiga) or yellow (Apple) and blue instead of black (Amiga). Could it be that IBM set the black/red/yellow standard and eventually everyone else followed?

Phone standards were probably once set by monopoly phone companies and then became unwritten law. They're occasionally subject to change though.