Aluminum Wire

[MikeDubreuil]

Originally Posted by http://forums.usfirst.org/showthread.php?t=519

Q:The rules state that any amount of additional wire may be used, provided it is of proper gague or larger, and properly color coded. Must the conductors be copper?
A: Aluminum wire is not permitted. All the specifications are based on the use of copper wiring for all electrical connections.

Can anyone provide anything in the manual that explicitly mandates the use of copper wiring? If this is the rule it should be made clear in a team update.

[Elgin Clock]

Besides the fact that it is in the rules, and it is not to be questioned.. lol

This is a good enough reason for me.

During the 1970's, aluminum (instead of copper) wiring became
quite popular and was extensively used. Since that time,
aluminum wiring has been implicated in a number of house fires,
and most jurisdictions no longer permit it in new installations.
We recommend, even if you're allowed to, that do not use it for new
wiring.

http://www.faqs.org/faqs/electrical-...ection-16.html

&

http://homerepair.about.com/od/safety/a/alumwire.htm


Seems kind of dangerous. I'm not using that on my robot.

[MikeDubreuil]

Seems kind of dangerous.

From my research the problem is not with the wire itself but at the connections. Environmental changes can change the physical properties of the aluminum wire causing the connection to loosen, resistance to go up, heat to be generated, and then ignition.

See:
Aluminum - Household Wiring

I'm not advocating the use of any kind of wire. I'm just an advocate for the horse before the carriage. If FIRST wants only copper wire to be used then there should be a rule for it. The Q/A system does not create rules, it only clarifies them. Manuals and team updates create and modify rules. I understand that in years past there has been a rule that limits teams to only use copper wire. However, we all know that previous years rules don't apply to the current year.

[Mike Betts]

Originally Posted by MikeDubreuil

Can anyone provide anything in the manual that explicitly mandates the use of copper wiring? If this is the rule it should be made clear in a team update.

Mike,

In answer is no but perhaps there should be.

Here I go again…

Disclaimer and preemptive apology: I know you to be a very competent engineer and you are already aware of many of the points I’m about to make. I apologize as the tone of this (rather lengthy) dissertation will appear condescending but I offer it for those teams which have a limited engineering mentor base…

This response is part engineering, part legacy and part common sense..

Legacy:

Originally, we were only allowed to use the wire provided in the KOP. Then, FIRST allowed us to purchase additional wire which had to exactly match the KOP wire.

In 2003, FIRST supplied us with wire and modified the rule to "The wire supplied in the Kit is to be used to conduct electricity. The chassis of the robot is not be used to conduct electricity. You may use additional wire as long as it meets the gauge and insulation color requirements." All wire in the kit was copper...

There was a conscious effort at FIRST to reduce the size of the rule book. We, mentors and engineers, asked for this…

Today, FIRST no longer has hookup wire in the KOP and specifies only minimum AWG.

Engineering:

From the mid 1960’s though the early 1970’s, the NEC allowed aluminum wire to be used in residential housing. It seemed like a good idea at the time. Copper prices were becoming astronomical (or so it seemed back then).

A lot of houses burnt down…

1. Aluminum wire has a higher coefficient of thermal expansion than copper. As a result, the lug connections will loosen and fail easier than with copper.

2. Aluminum has a higher resistivity than copper. For a given insulation type, you need a larger conductor to service a load safely.

3. Aluminum is more flammable than copper.

4. Aluminum wire is subject to micro fretting and has an increased risk of arcing.

Back to burning houses… The U.S. Consumer Product Safety Commission estimates that homes with aluminum wiring (pre-1972) are 55% more likely to reach “fire hazard conditions”.

After 1972, aluminum alloy wires were introduced as well as special sealing compounds for aluminum. This mitigated but did not eliminate the expansion and fretting problems. Also, the NEC restricted the use of aluminum wire to “single purpose circuits” such as central air conditioners, electric ranges and main electrical services.

Lastly, manufacturers of electrical connections designed wire clamps to “spring” and compensate for the aluminum expansion. However, these aluminum rated connections are usually confined to the aforementioned “single purpose applications”.

As such, most general purpose clamp and crimp connectors are rated for use with copper wire only. This includes, to the best of my knowledge, all of the connections and connectors we are given in the KOP.

In order to safely use aluminum wiring on a robot, a team would need to reengineer the entire connection system. This task is outside of the abilities of most teams…

Common Sense:

FIRST has based its wire sizes (and much of its power distribution design) on automotive industry standards.

Companies like Ford, GM and Toyota have the ability to assign hundreds (thousands if you count Tier I suppliers) of engineers to design their power distribution systems.

If they could save a few dollars and a few pounds from each of millions of automobiles by switching to aluminum wiring harnesses, wouldn’t we be driving in them?

Bottom line:

Perhaps FIRST should specify “copper wire only” and perhaps they should add some words to the effect of “use proper engineering judgment”…

At any rate, I would recommend against attempting a switch to aluminum wire on a FIRST robot.

JMHO,

Mike

[MikeDubreuil]

Thank you for the kind words Mr. Betts, I'm sure that many teams will find your dissertation useful. For those who are curious, my team uses Ultra Cable from Street Wires for connections to motors in the kit. It is made from tinned copper but looks like aluminum wire.

My concern with the aluminum wire answer from the Q/A is that there is no rule backing up the answer. Perhaps I am misinformed but the Q/A system does not make rules, it just clarifies them. Rules come from the manual. Rule changes come from team updates. This year I will be a robot inspector at the Boston Regional. Therefore, if a team comes to the Boston Regional with a robot with aluminum wires have they broken a rule?

[Mike Betts]

Mike,

I agree that they should make a change to the rules.

Slightly off topic: I have had a problem with the Q&A system for a couple of years now. My problem is that, if a team presents a Q&A of a particular post, the inspector will generally accept it as "law".

Since FIRST changed to the online Q&A system, I have asked repeatedly for a downloadable, seachable Q&A document... No joy.

As such, I have not volunteered as an inspector and really sympathize with those who do that job. They are are at a disadvantage...

Mike

[Alan Anderson]

In light of the Q&A, a robot wired with aluminum will almost certainly be judged as breaking rule <S01> due to unsafe design.

[Richard Wallace]

Originally Posted by Alan Anderson

In light of the Q&A, a robot wired with aluminum will almost certainly be judged as breaking rule <S01> due to unsafe design.

I agree with Alan that a robot wired with aluminum would be unsafe and would therefore violate <S01>. However, as written, <S01> is enforceable by the head referee, not the robot inspectors. Some head referees may choose to delegate that authority. To address Mike DuBreiul's question: if you were on my inspection team in St. Louis, I'd ask you to let me know if you see a robot with aluminum wiring, and to tell the team it is unsafe. And I'd let the head referee know about the safety risk.

Every head referee I have worked with has given safety on the field very high priority. In one case (2005 STL finals) the head referee called for an on-field inspection of a robot drivetrain unit that appeared to have become unsafe. Based on the inspector's recommendation, he required the team to disable the suspect motor before proceeding with the next round.

We all need to thank Mike Betts for the fine summary on aluminum wiring that he provided above in this thread.

Back to Alan's point: aluminum wiring is just one example of how a "catch-all" safety rule helps put some common sense about good engineering practice into our design thinking.

[Al Skierkiewicz]

Gentlemen,
This may be a mute point, but I haven't seen AL wire in #14 or #18 or even #12 for quite a while. It may be that AL wire is not code in Illinois or in Cook county. If it is not readily available to all teams, it is not included in acceptable materials. (BTW, throw the rules out as they apply to AWG and breaker choice.) As to the Q&A, I have always been of the opinion that the Q&A answers questions that not only relate to the current manual, but to questions that were not thought of during the documentation process. As such the voice of authority is either First or the GDC when answering Q&A. Additionally, the Q&A often drives modification to the manual and team updates. Hence the two per week team updates and the fact we are already up to Rev D on the Robot rules. As an inspector, I bring with me, searchable files of the Q&A, all team updates and the latest revisions of the manual sections. I require that any team who claims a particular device was allowed in a Q&A to prove it by showing me a copy of the Q&A or searching my files.

[Gary Bonner]

Originally Posted by Al Skierkiewicz

...As an inspector, I bring with me, searchable files of the Q&A, ...

Are searchable files of the Q&A available? I didn't think they were.

[Mike AA]

Originally Posted by MikeDubreuil

Can anyone provide anything in the manual that explicitly mandates the use of copper wiring? If this is the rule it should be made clear in a team update.

While use of aluminum would not be dangerouse, it is not exactly cost effective. With aluminum wire you would have to go to atleast the next size wire, as aluminum doesn't conduct as well or carry current as well as copper. Also, you would need to use de-ox on EVERY copper connection so as to prevent oxidation. You would likly save very little by using aluminum wire, if you can even find it in the required sizes.

Coming from an electrician I am telling you do not use aluminum. Use copper. As to it being cause of fire, this is partially true. Older homes had/have aluminum wire as it was cheaper, problem is if recepticles and switches weren't rated for it, this would cause problems. Aluminum devices are still available but much more expensive. Many services serving houses and some businesses use aluminum for the service conductors, 100% safe and being its only 10-30 feet there isn't worry about it being larger as the NEC hase code for this.

-Mike Aalderink

[Schneidie]

Originally Posted by MikeDubreuil

Can anyone provide anything in the manual that explicitly mandates the use of copper wiring? If this is the rule it should be made clear in a team update.

Aluminum is bad. It heats up , corrodes, does not work well eith Copper crimp connectors and does not carry charge very well.

You can use it if you want, but I would advise against it.

[Cory]

Originally Posted by Schneidie

Aluminum is bad. It heats up , corrodes, does not work well eith Copper crimp connectors and does not carry charge very well.

You can use it if you want, but I would advise against it.

No...

If you had read the original post in this thread, you'd see that you CAN'T use aluminum wiring.

[Al Skierkiewicz]

Originally Posted by Schneidie

Aluminum is bad. It heats up , corrodes, does not work well eith Copper crimp connectors and does not carry charge very well.

You can use it if you want, but I would advise against it.

These are all misconceptions. Aluminum is OK, it is used in specific areas of the electrical industry all the time where the properties are advantagous for the application. Aluminum doesn't heat up but bad connections where the joint loosens do heat up because of local high resistance. (This can occur with copper and does occur all the time on robots.) Aluminum oxide is conductive but aluminum is subject to the same electrolytic action other metals are subject to under similar conditions. It can be crimped very well but has a different heating expansion/contraction coefficient than copper which cause problems over time. It is only slightly higher resistance than copper but much less than brass which is used all the time for electrical as well. (aluminum is about .0017 ohms per foot vs .001 ohms for copper #10 wire, hence the need to use the next higher guage for the same current.)


Gary,
One of the mentors on my team has been able to convert all the Q&A into a Word document for me in the past. I am not sure if the current system will allow that but FIRST should make that possible. Then it was necessary to do a key word search for an item or a section number.

[Evil Robotics]

Copper oxide conducts electricity, aluminum oxide does not, therefore if you come across house wireing and do not have the means to replace it be diligent to coat the AL wire with oxide inhibitor.

Also be aware aluminum wire will not take repeated flexing as well as copper.

As with welding alumnum the oxide doesn't conduct and therfore needs to be removed. If it is not cleaned if will generate heat across the AL oxide. That is also why rookie welder often blast thru before the heat is high enough to make a good weld.

Most house main input feeds into the load center are copper plated Al. In my house they are raw AL. Also most grounding rods (pounded into the ground) are also copper clad AL. It is basicly done to save cost.

I do not recommend using Al wire on FIRST robots.

Knowledge is power but ingnorance is false bliss.

I just wish I knew how to spell.