bad or good idea?

We all know that copper cost are still up...We are going to install a new panel, 8sets of 250 MCM (about 500ft run), what are your thoughts on aluminum instead of copper? or should I not even bring it up....


Edit: 6 sets not 8

It depends. On a lot of things, not the least of which is the enviornment.
Other criteria to asses include How good is your electrician/contractor at properly terminating Al? What is the mechanical load (vibration) likely to be? How long do you plan on the installation being in service?

My best suggestion would be to actually speak with an engineer from the company providing the cable, and see their thoughts. Almost all companies that make large constructions have very good applications engineering departments.

I wouldn't have considered AL years ago, but time has changed.

I was in a plant ten years ago that had four cables run through the plant instead of busbars, and you just tapped in with split bolts. The had the utility jack up the power to 488 volts where it was supplied in the center, and the two outlying ends were 463 and 436 volts when the plant was running. Thew cable was sized for the original 1963 requirements, and by the 90's, was grossly overloaded.

Had one engineering company spec 4/0 with fiberglas insulation to save money over 535mcm runs.

A good contractor or supply house may be able to come up with a cost effective solution for you.

regards.....kc

In the past 3 months, I have switched to aluminum for main panel feeders. I have specified 600 MCM aluminum cables with 90-degree C insulation, good for 385 amperes per cable. The terminal lugs and terminal points must be rated for use with aluminum.

I also plan to use 17 runs of 1000 MCM aluminum cables for a 2500 kVA transformer-to-switchboard feeder in a pre-cast surface cable trench.

Just a word of warning regardless of which route you go. Wire theft is on the rise big time. A customer of mine had someone break into a control van at a rock quarry that had MCCs in it. The thieves knew that the site was generator powered so nothing was live. They stripped out every conductor inside, including the MCC bus bars and aluminum feeder cables going to large crusher motors. And it's not just the cost of the wire itself, they stripped even the control wires so now everything must be rebuilt. Being that they knew how to remove the MCC buckets to get at the bus, I'd say they were electricians that did it too. Sad state of affairs.

There is nothing wrong with using aluminum conductors as long as it is properly installed. The problem is, aluminum conductors are not always properly installed. The most common problems with aluminum conductors is expansion and contraction due to heat can loosen connections and oxidation.

Some things to note – You will end up using a larger size aluminum conductor to obtain the same ampacity of a copper conductor. Make sure you apply the adjustment factors for number of conductors and the correction factors for ambient temperature. Make sure your connections are rated for aluminum. Make sure you torque the connections according to the manufacture’s recommendations. Make sure you clean the conductors properly. Make sure you use an anti-oxidizing compound. Make sure you don’t use a temperature rating greater than the connector rating. Not all connections (lugs and such) are rated for 90C. If you have a THHW conductor, which is rated up to 90C but are installing it in a lug rated at 75C, you need to use the 75C ampacity rating of the conductor.

In the end, make sure you (or someone) knows what they are doing, there is a lot more involved in determining conductor size than just looking at Table 310.16 in the NEC.

Correct me if I'm wrong, but isn't aluminium going up in price as well?

Tark said:

There is nothing wrong with using aluminum conductors as long as it is properly installed. The problem is, aluminum conductors are not always properly installed. The most common problems with aluminum conductors is expansion and contraction due to heat can loosen connections and oxidation.

Some things to note – You will end up using a larger size aluminum conductor to obtain the same ampacity of a copper conductor. Make sure you apply the adjustment factors for number of conductors and the correction factors for ambient temperature. Make sure your connections are rated for aluminum. Make sure you torque the connections according to the manufacture’s recommendations. Make sure you clean the conductors properly. Make sure you use an anti-oxidizing compound. Make sure you don’t use a temperature rating greater than the connector rating. Not all connections (lugs and such) are rated for 90C. If you have a THHW conductor, which is rated up to 90C but are installing it in a lug rated at 75C, you need to use the 75C ampacity rating of the conductor.

In the end, make sure you (or someone) knows what they are doing, there is a lot more involved in determining conductor size than just looking at Table 310.16 in the NEC.

Click to expand...

Good post!

I have installed Al conductors many times in the past... No really, I have had some people who knew how to do this install them for me. There is a lot involved but you can save sometime 50%

hmm... copper will be always better than alu and gold better then copper

is it possible to use alu instead copper properly?
a) if yes... will customer prefer cost or quality?
b) if no... will you dare to use alu anyway?

marius said:

hmm... copper will be always better than alu and gold better then copper

Click to expand...

Contrary to popular opinion, gold is actually a poorer conductor than copper. Gold is good for connections because it does not oxidize. Of the pure metal elements, silver is the best conductor.

For your reference, here is the resistivity of some metals:
Silver 1.628 micro-ohm*cm
Copper 1.724 micro-ohm*cm
Gold 2.44 micro-ohm*cm
Aluminum 2.828 micro-ohm*cm
Molybdenum 5.78 micro-ohm*cm
Brass 6.21 micro-ohm*cm
Iron 10.1 micro-ohm*cm
Steel 12.7 micro-ohm*cm

The resistivity of air is 3 gigaohms*cm


so you really don't need any condutors at all, just more air.

Sorry, I couldn't find the resistivity of beer to try to determine how much beer you would need in a pipe to equal 250 kcmil (no longer called MCM) but it would probably be enough to keep us all happy for a while .

brucechase said:

The resistivity of air is 3 gigaohms*cm


so you really don't need any condutors at all, just more air.

Sorry, I couldn't find the resistivity of beer to try to determine how much beer you would need in a pipe to equal 250 kcmil (no longer called MCM) but it would probably be enough to keep us all happy for a while .

Click to expand...

Thanks, Bruce... I'll just tell the electrical contractor just bring beer...we can make our own power:beerchug:

OK on a more serious note: I am attaching a picture (at least I hope I will) that is showing what happened on my new (4 year old) house in which the electrical contractor installed an aluminum set of wires from the breaker to my oven/stove. Luckily I was at home when my wife screamed at me that the oven was on fire (I just thought it was her normal cooking) . When I went into the kitchen, it was the unmistakeable smell of electrical burning. There are several problems with this install other than the aluminum attached to the copper with UNAPPROVED wirenuts. I know that no one attaches 250 kcmil with wirenuts, but my point, just like everyone else's in this post, is that the wrong person doing this will cause a catastrophe!!!. Imagine you facility feeder arcing and then catching on fire because someone did not properly install the aluminum conductors. I'm sure the money saved will be long forgotten. I'm not sure I would take the chance of installing the aluminum. I know copper 250 kcmil is running about $5/foot single strand. I don't have triplex armored pricing nor does my price list show aluminum. Of course prices change daily and my price list is a couple of months old so I'm not even sure it is accurate. I guess the first question is how much will you save?


OK I knew I couldn't upload the picture:smas:



It only took me 30+ minutes to post this. I'm sure I won't remember next time I try to do this. Anyway, back to installing new I/O on a conveyor system. Only have a couple more days to get it in and checked out. By the way, I am using copper for that job.

[Rant Threadjack]
A couple of years ago during a facilities expansion new switch gear was added. An existing 1500A panel was to be backfed from from the new gear. It was February and someone from the contractor slapped a meter on the existing gear, saw that it was drawing only 450 amps, and decided to downsize it to 1000 amps to save a few bucks on copper and breakers for the new feeder to the 1500A panel. A bean counter, ie, a genuine electrically clueless accountant, approved it and didn't check with our facilities people (There are 3 100 HP, 8 50HP motors, and perhaps a dozen 25HP motors on that panel, not counting AC and lighting loads - of which some must have been off when they measured).

Fast forwared to the present day; we are experiencing regular outages for the part of the facility which is fed by the downgraded panel. We get the same contractor in here to bid on fixing it and he says "Well it was never intended to have that kind of a load on it." I felt like slapping him. The load is what the load was - and it doesn't matter what he intended, it matters what we needed. As far as I am concerned, his attitude cost him the opportunity to be considered for the job.

Now with the price of copper, we are looking at a huge bill to get the problem straightened out. [/rant threadjack]

Tark's input just about says it all.

IMO, or $00.02 is the key to using aluminum conductors is 3 simple steps, "PROPER TERMINATION, PROPER TERMINATION and PROPER TERMINATION".
I have seen many transformers wound with aluminum working just fine. With the advances in metalurgy I would imagine that aluminum conductors might work right well in some applications. I have not yet seen it anywhere. I imagine it is only a matter of time.