Wire color...

Technical Electrical
#1

Hi All,
Once again I find myself apologizing for asking a question whose answer may be easily found… …by someone but not by me.

Is there any rule that defines the wire color between a motor and its driver device (a Jaguar, in my case, but the question applies equally well to Victors and Spikes)?

I know that 12V and ground going TO the motor driver device has to be certain colors by rule but I could not find anything that defined the color going between motor to driver. I also know that there are rules on minimum gage (based on fuse size, if I understand it correctly).

Finally, I also understand that, generally speaking, in FIRST rules, what is not forbidden is allowed, but I fear that I have missed something.

Thoughts?

Joe J.

#2

There is no such rule prescribing wire colors for ControlDevice->Motor wire, as polarity shifts here. You are allowed to use any colors, however, its common for teams to use all black, Red/Black signifying the forward direction, or some non-Red/Black color.

#3

Joe,

<R48> All active Power Distribution Board branch circuit wiring with a constant polarity (i.e., except for relay module, speed controller, or sensor outputs) shall be color-coded as follows:
A. Use red, white, brown, or black with stripe wire for +24 Vdc, +12 Vdc and +5 Vdc connections.
B. Use black or blue wire for common (-) connections.

You can use any color you choose for the output side. Red and black can get confusing if you change the motor polarity at the output of the controller. Still red and black wiring keeps you from having to buy additional colors.

#4

On the contrary Al… we find using two colors to be helpful and to help avoid confusion. If you need to disconnect something at any point from the speed controller, hooking it back up could be confusing if both leads are the same color - potentially hooking it up backwards could be an issue.

IMO (which is not the opinion of the GDC or the inspectors), It’s always beneficial to use two colors for motors, and always have them wired to the speed controllers in the same way (red to the M+, black to the M-, for example). This way, you can avoid mistakes a lot easier, and ensure you always hook it up the same way for your programmers (or they’ll hate you when they have to change the direction of things in code constantly).

#5

Jon,
I was not implying to use the same color for both output terminals simply that the color code does not cover the speed controller outputs. We use red/blk pairs for everything and make the direction changes as needed at the motor end of the wiring.

#6

Avoid using green. In our rookie year, we used green between Victors and motors because we had a large supply. At inspection the inspector said that green was reserved for ground (which he just made up, this was nowhere in the rules) and made us rewire all the motors. Probably wouldn’t happen again but best to be safe.

#7

Jeff,
I would have made that same assessment. Green or green with yellow is a universal color for safety ground that implies a low impedance connection to a ground rod or water pipe. It is also the wire to which you should attach a ground fault interupter. Although there is no robot rule that covers this color, we do want to keep students using standard color codes so they don’t get in trouble elsewhere.

#8

I think this is too strong of a statement. Automotive wiring uses green in many places for wires other than ground. Automatic equipment mfg do not limit themselves to non-green colors within their PLCs. There is a lot of green wire out there being used in non-safety ground applications.

If there is no rule against it, I think it should be allowed.

Joe J.

#9

This is dead wrong. It is not the inspector’s place to make up rules on the spot based on his own personal opinion just to teach a lesson. There are very few water pipes and GFI’s in an FRC robot. If he wants to teach a lesson about house wiring and encourage students to not use green wire then he is free to offer that advice, but you do not make up rules and force teams to rebuild their robot at a tournament because you feel they used poor practice. There are 1000 rules of thumb about good mechanical and electrical practice that are not in the rules and you cannot ask teams to accommodate the pet peaves of every inspector. As a mechanical inspector I would not force a team to put lock washers under their nuts even if I felt strongly that they should, because it is not in the rules and it is not my place to add it. If the GDC intended for a wire color to not be used they would put it in the rules. The inspectors have a checklist for a reason.

#10

Whoa Tex,
I didn’t say I would make the team remove it. I said I agreed with the assessment that green is a color used for safety ground. As such I would inform the team of my assessment and let them decide. Inspectors do have a responsibility to try and help teams. We are on the front line to help you be competitive because it is best for all involved. As green is often thought of as being a common/earth/ground/safety, an electrical person would walk up to help you troubleshoot and naturally think that the green is tied to battery common. If used in the output of a speed controller, that could allow a person to tie a meter or other electrical device to it thinking it was common and find a pulsed 12 volt signal there. Smoke may follow. In auto electrical, as Joe has pointed out, there are other color codes.
As always, teams have the right to question the inspector and ask the LRI for a ruling. An LRI will usually include the head ref and FTA in discussions that transcend the rules. As much as we try to help, teams often disregard our advice. A testament to this is teams who mount the breaker panel upside down and have breakers fall out or teams that attach chain sprockets directly to the shafts of CIM motors without the use of additional bearing surfaces and have the motors fail during a finals match. The list is long, these are just a few.

#11

Ok. He said the inspector made them rewire it, and you said you agreed with that assessment.

#12

Our policy is to use different connectors on the wires so that there is no way of hooking anything up backwards. This can be a big problem if there are 2 cims in the same gear box that run opposite of each other.

#13

in that situation (two CIM’s that have to always run opposite each other), we would handle it in code, and still have the red lead go to the M+ and the black to the M-. What do you mean by different connectors?

#14

We generally use all yellow wires to go from our relays/speed controllers to our motors. I’d say about 50% of inspectors express a concern over this, so we politely point out that the reason we do this is to alert people that we don’t know whether the wire is going to be + or - at any given time, and explain how the relay and speed controller work to change direction of the motors.

Usually that satisfies them. They come away knowing a bit more about robots and FRC inspections (many are doing this for the first time and are just trying to be thorough), and we’re happy to help educate them about the reasons for our choice. If they still have concerns we advise them to discuss the matter with their lead inspector, check the rule book, and get back to us.

We’ve never had a problem.

Well, with coloured wires, that is. We used speaker wire once many years ago (only “downstream” of the controls), and the lead inspector did raise a concern that it had a different fire resistance rating for the insulation than did the less flexible automotive/home wiring. It turned out his concerns were based on the fact that he had built speaker wire into the walls of his house and then had a building inspector make him rip it all out.

We pointed out that all of our wires were significantly larger diameters than required by the rules, and that the wires were not buried out of sight in an insulated wall, so the chances of overheating were essentially zero. This was a big deal as the wiring runs were not going to be replaced in less than four to six hours of intensive work, and we needed that time for other issues.

Note that we kept our sarcastic comments about the state residential building code not really applying to robots to ourselves and, while firm with our arguments, went out of our way to be respectful.

Thankfully the lead inspector, with the encouragement of the tournament director, sought a second opinion “from FIRST” on Thursday night. I don’t know who they called, but: a) we passed tech WITH the speaker wire and b) we’ve been very conservative with our wiring choices ever since.

FIRST usually makes the right call, if you give all the volunteers a chance to do so by being polite, listening to what you’re being told, and presenting a calm, reasonable explanation of your position.

Jason

#15

Jason,
It really depends on the speaker wire but what is of prime importance is the ability of the insulation to withstand voltage breakdown. Most wire is capable of withstanding 300 volts which we never achieve. Speaker wire is generally unrated but typical home systems running 100 watts per channel can easily peak over 80 volts P-P so the wire is able to handle that. Building inspectors following most electrical codes expect/demand that any wiring over 25 volts must be in conduit. It is for this reason, that PA amplifiers have a 25 volt output as well as a 70.7 volt output. It doesn’t change the fact that higher voltages are present, but make the inspector happy. In many states, conduit is not required in residential installations. Minnesota is one of these and the wire used is a dual insulation type.

#16

Ouch. I happen to fall into this boat; we considered everything that could fall/hang/dangle off/down/from the robot’s electrical system (which was mounted upside down as a safety measure against balls and to save space on the robot) - however, I guess we never considered the breakers falling out since we have a hard time pulling them out by hand as it is. But, I guess I can see how this is just another thing we need to consider. Any suggestions on how to guarantee the breakers don’t fall out, other than mounting the board right-side up? Has that been a problem with the new Power Distribution Boards?

-Danny

#17

Danny,
I was speaking to the old fuse blocks. The new PD holds pretty tight until it has been used repeatedly. However, if your robot comes off the bump hard, it might pay to think of a way to put a piece of lexan over the breakers that will not obstruct their view for inspection.

#18

In 2005 we mounted all of our electric upsidedown and we had no problem with fuses falling out. We also used ruber bands to help hold in the PWM cables. This year every thing is mounted upsideright and our fuses have almost fallen out many times. We have to keep checking them and pushing them back in.

#19

Joe,
Are you using a new PD or last year’s?

#20

We are using the new one.

I have never seen a game shake up a robot as much as this one.