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Author Topic: Using Aluminium instead of Copper for high amp 12v  (Read 2950 times)
Nissan_DownUnder
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« on: September 11, 2007, 01:34:23 PM »

Good Morning  Smiley

One of my neighbours recently replaced the main cable to his workshop with new underground cable ( 3 phase 240v).   Due to the high cost of copper here the electrician used aluminium cable.  According to them  Al cable is just as good as Cu, you just allow an extra 20% cross section in the size.  At the end of the job they had 11 metres (35') left over, which the owner has given to me.  This just happens to be the length of my bus.

The cable is 4 core each core is approx 200 sq mm.  Given that 4/0 cable is 104 sq mm, I calculate that this cable should easily handle my expected 12v load ( max 2400 watt).

The electrician also gave me 1/2 a box of the appropriate connectors to terminate the cables.

Given the very high cost of copper here and the fact that this Al cable is free, I am very hopefull that it will work.

As normal, I would appreciate an comments from members of the board.

Regards
        Peter
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Peter
Nissan UA440,  Wellington, New Zealand
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« Reply #1 on: September 11, 2007, 01:51:52 PM »

I'm sure it will work fine from an electrical point of view - the only concern would be the fact that the malleability of aluminium is extremely low compared to copper, so you will have to be careful when laying the cable to avoid bending it as much as you can - and certainly don't bend it in the same place more than once if you can possibily avoid it.

Overhead power lines are generally aluminium I believe (where obviously weight saving is an issue too) - it will be interesting to see if it becomes more commonplace in other applications too - although the cost of aluminium itself is also rising quite rapidly. It so happens I weighed in 90kg of scrap aluminium from my bus yesterday - mostly seat rails and lengths of extrusion that held the ceiling panels and luggage racks. I got £73 (UKP) for it, which I was pretty happy about - makes a change for the bus to earn money rather than absorb it.

Jeremy
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« Reply #2 on: September 11, 2007, 03:41:24 PM »

Hi Peter,

Thanks for posting!

If you were to use the aluminum cable, just keep in mind that aluminum is very soft and will get loose in any connection especially

in a moving vehicle. They make an anoxicedent paste to keep your connections fron corrodeing. Use It!  Furthermore, it would be a safe practice to retighten

all your connections at least twice a year..... Loose connections can and will cause fires!

Be Safe!
Nick-
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« Reply #3 on: September 11, 2007, 06:09:06 PM »

Peter,
Don't blow off Nick's advice to use the antioxidant paste.  Also, you should leave a loop for absorbing any motion or vibration.  Other than that, I suggest "eyeballing" it once in a while and checking for tight connections.
Dennis
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« Reply #4 on: September 11, 2007, 07:42:02 PM »

Aluminum wire carries high voltage much better than low voltage and high current.

Power lines are done with it and the line voltage is very high 4,800 volts and up
that keeps the current low.

That's not to say that using aluminum is good or bad, But years ago when aluminum wiring came out for mobile homes and new construction, It was banned in many places because of fires started by wiring problems. Aluminum melts around 700 degrees
copper is much much higher. It's a matter of density..

I stay with copper, The price is cheap when compared to potential loss...

Dave....
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« Reply #5 on: September 11, 2007, 07:48:49 PM »

DrDave posted while I was typing, but here is my input anyway.

For stationary use, like home or shop, aluminum works ok - most of the time as a service entrance.
BUT, how often are you pulling the rated load at home? Running 200 amps thru the alum wire will heat it faster than if it was copper. This heating is not good.

I lived in a house that was wired with aluminum only. I saw more failures in the wiring than you'd believe. Wires would break inside a wall with no known cause except fatigue failure from thermal cycling. I'm still amazed it didn't burn down.

I wouldn't use the aluminum for several reasons:
It expands & contracts more than the metal in the clamp & thats one of causes the need to continuously retighten the clamps. You are suppposed to torque the clamp to a specified value - over torque will crush the wire & make it loosen quicker from the thermal cycles.
Aluminum will suffer fatigue from the vibrations & eventually break - may take a few months, may take years or longer.

In summary, the savings aren't worth the potential hassles & loss for my conversion.

The cost of the copper wire isn't that big for what you get.

But I'm no electrician, so this is just an opinion.
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« Reply #6 on: September 11, 2007, 08:17:47 PM »

Peter, Kyle 4501 hit the nail on the head with his post. The expansion and contraction differences make aluminum very problematic.

 When it expands it causes a looser connection and becomes worse each time it happens. Overtightening/crimping is also a common problem as it reduces the circular mil area of the wire and decreases the current carrying capabilities.

 As long as there isn't a very large temperature difference (no large load or ambient) it works ok.

The National Electric Code forbids the use of aluminum in certain instances.

I personally wouldn't use it.

Sept. 18th will be my 39th anniversary working as an electrician.
 I've seen a lot of failures attributed to aluminum that wouldn't have happened with copper.

Ed
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« Reply #7 on: September 11, 2007, 09:23:28 PM »

All of the information that I have seen posted I would find to be accurate. The only addition that I would make is to mention that MOST of the problems associated with aluminum wiring in homes is related to SINGLE STRAND ALUMINUM not multi strand aluminum. I'm sure you are working with multi strand aluminum and the newer aluminum wiring is made from better alloys that are not as problematic as older aluminum wire. HOWEVER I personally would heed all the cautions that have been given and I would probably use it if it were up to me --- Just an opinion and it probably isn't worth much.

YMMV

Melbo
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« Reply #8 on: September 11, 2007, 09:47:32 PM »

Thank you all for your input.  As I expected, you have give me a greater understanding of the pitfalls of of using the aluminium. The wiring is multi strand

Generally I am very open to using new ideas & experimenting.  However, the bus is taking a lot of work & will be home to my family when we are touring.  If the risk was of the wiring simply not working, I would accept it, but given the risk could be a fire if I get it wrong.  I will let someone else run this experiment.

Thanks again for all the advice.

Cheers
       Peter
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« Reply #9 on: September 12, 2007, 12:16:28 AM »

Peter,

Given that you have already made your choice, I will save my breath except to applaude your decision.  I too had a house with alu wiring.  My sterio system was great but not outlandish and every time a serious base note was hit in a song you could detect a flicker in the lights.  $.5 M condo!!!!! go figure.

Best wishes on your project.  Your reservations about fire are well placed as I have friends that barely escaped and in each of those instances they were awake and clothed.  Both were propane but still.  In both a flare fitting cracked at the "single flare".  Always do double flares no matter what and pay attention to how tight you torque the fitting as you can work harden the copper as well as mash it flat.  It is usually the simplist things, no?

John
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« Reply #10 on: September 12, 2007, 03:23:33 AM »

That's what I like about this board. A person explains what he or she wants to do and a friendly discussion takes place. The facts mentioned are not to be ignored, glad Pete made the right decision. The wealth of knowledge from those posting answers is fantastic. I always learn something, hopfully it will also benefit those who are contemplating building their own dream bus.

Paul
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« Reply #11 on: September 12, 2007, 05:30:49 AM »

A curious thing is that utility companies run aluminum underground from the transformer to the meter pedestal and the NEC requires copper of twice the size from the meter to the house. Shouldn't those overloaded/aluminum wire pedestals be on fire?
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« Reply #12 on: September 12, 2007, 07:12:54 AM »

A curious thing is that utility companies run aluminum underground from the transformer to the meter pedestal and the NEC requires copper of twice the size from the meter to the house. Shouldn't those overloaded/aluminum wire pedestals be on fire?

Utility companies generally use thier own rules. It's thier equipment and they do what they want.
( Called cost vs effect )... Once the meter is installed, they technically own everything up to your breaker box since they control all wiring to that point.

Most of the people that do the line work are not electricians and are not expected to follow codes from the book, They are provided training on entry hookups and the engineer is the one that takes the blame if accepted practices are not followed.

My stuff is all copper from the weatherhead, Because I had to provide that part including the meter housing installation and main panels. So they hooked aluminum from the pole to the weatherhead, It's their problem from that point back.
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« Reply #13 on: September 12, 2007, 07:35:07 AM »

Dr. Dave is right, everything from the transformer is paid for and installed by the customer (American Electric Power).

They give you a sheet with all the info needed to do your service and it is based on the NEC. If not done to their specs they will not hook you up.

Utility companies are not bound to comply with the NEC, they are exempt. NEC 90.2 (B) (5)

The wire they use for a service drop is usually areial wire and different from house wiring.
 Also it is considered single conductor in free air and according to the NEC, wire current carrying capacity from that chart is different than multi conductor, in a a raceway or concealed in walls.

 For instance # 12 copper that we use is rated for 20 amps, but # 12 copper as a single conductor in free air is rated at 60 amps NEC Table 310.21

The standard rule of thumb is, when you go from copper to aluminum go to the next size larger, ie: from #12 copper to #10 aluminum.

Ed
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« Reply #14 on: September 12, 2007, 08:13:08 AM »

Apparently I wasn't specific enough in my comment. In south western Arizona it is common to have meter pedestals because many lots get a mobile home which doesn't have a meter socket so the developer puts in meter pedestals.. The power is generated and supplied by Arizona Public Service (APS) and they provide the underground aluminum cable to the meter socket which feeds a main breaker below the meter. From the main breaker NEC (and/or local regulation) requires copper underground of a size which is more than two sizes bigger than  the aluminum feeder to the meter.

My comment referred to the reduced current capacity, the loose connections and the overheating of aluminum that doesn't seem to be a problem in these installations.

I might also point out that I live in a 35 year old house that has all aluminum wiring that has not been a problem. Some houses in the area have had problems with it and my personal opinion is that the quality of components used and the quality of workmanship made a big difference.
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