Metric Hardware

[ravichauhan]

This was posted by one of our mentors on our team forum:

I have a bag of metric nuts for the power blocks. These need to be colored with a blue sharpie and used to replace the current hardware. A free soft drink to the first person who can tell me why we shouldn't color them green.

Anyone have any ideas?

[Chris is me]

Green is a legal color for wire, blue is not. Green would imply a particular polarity needs to go through the Metric nut.

[kstl99]

Originally Posted by Chris is me

Green is a legal color for wire, blue is not. Green would imply a particular polarity needs to go through the Metric nut.

Wouldn't green imply earth ground?

[EricH]

Sorry, Chris. Blue is a legal color for ground per 2010's <R48-B>, as is black. Green is not legal on PDB branch circuits (red, white, brown, or black with stripe is legal on + connections, <R48-A>). (NOTE: May change for 2011, does not apply to non-PDB circuits like sensor returns)

Green implying earth ground is not relevant for FRC robots, as they don't have an earth ground unless it's specifically installed, and then it's typically a drag wire attached to the frame.

Given the question, I'd guess that green is a team color code for something else--and green is currently on the robot.

[ATannahill]

It might be that your mentor is trying to teach you not to use green because it does stand for earth ground in the professional world.

While it is not listed in the rules, I would suggest never using green because it may confuse someone that is not familiar with FRC or it might carry forward with someone who later uses green inappriately outside of FIRST.

[ravichauhan]

So to confirm, it would be because green means earth ground?

[Karibou]

On a related note: We have a set of metric alan wrenches, and they are blue-coated instead of the traditional gray/black that we are used to. After a quick Google search (er, several), it seems like blue is the color that is used to denote metric items.

I don't know anything about wiring. From what I can gather between google and my own experience, green could just be a random color. Your mentor might have said red, and it would not have made a difference.

I wouldn't trust this unless someone can back me up, though. How many guesses are you allowed?

[kramarczyk]

Unless the OP wants to disagree I'd say the green for ground wins. That it is ground in the real world is probably why it doesn't show up on the FRC color code.

Bonus points for Kara for figuring out that blue = metric.

[Al Skierkiewicz]

Green is the standard color in the US for ground. Electricians understand that the green screws connect to earth somewhere but do not actually represent a good earthing connection for equipment that actually requires earth for some particular reason. (RF suppression for instance) Electrical codes differ widely in different parts of the country and in different settings. Hospitals for instance carry very strict electrical codes for patient safety when connected to electrical monitors and other equipment. Your house may have green wires running to outlets, electrically bonded metal conduit and metal boxes, or a bare wire in romex or BX Cable (sometimes called Greenfield). Most codes call for that wiring to connect to a metal water pipe or ground stake near the electrical box.
As pointed out, there is no 'ground' on the robot. When coloring the hardware, be aware that the hardware may be providing electrical connection.

[Taylor]

We've got several hex key sets. For each of them, the metric is blue; the SAE is red.

I'm not a technician, but I'd wager this has something to do with it.