aluminum vs. copper

[that-guy]

need to run service wire from my house breaker to my detached garage. I'm running a 100amp breaker and am pricing out the wire needed. I am running copper all over on the inside, but the service wire is almost 5 times more expensive for copper over aluminum. what are the downsides of running aluminum over copper?

please keep the preference nut swinging to a minimum, just cold hard facts please

 

[Cmreschke]

Bigger pipe size, lug size, um.....yeah
Not that much of a down side really.
AL all the way imo.

 

[pattenp]

The biggest downside to aluminum is where underground (even in conduit) if the insulation gets damaged during installation exposing the wire to moisture/water, the wire will oxidize and fail overtime. Copper is a lot more resistant and will last much longer if exposed to water. With that said, the cost benefit of aluminum for long runs out weights the potential of failure. Power companies run aluminum underground all the time and is the norm. So, if aluminum is installed properly and with care not to damage the insulation during the install it will last a lifetime.

 

[wyliesdiesels]

AL feeders are the way to go unless u have money to blow on cu.

As pattenp said, the only potential issue is insulation failure. This can be mitigated by use of conduit for the underground run.

How long of a wire run are we talking?

If u truly need and want 100a in the garage, u will need a minimum of #1 AL. #2 AL is only good upto 90a in this application.

 

[bczygan]

Silver is better!

 

[Elginz]

As stated with aluminum "if the insulation gets damaged during installation exposing the wire to moisture/water, the wire will oxidize and fail overtime. "

With copper it just keeps bleeding off electricity and you won't know where, raising the bill with no idea what is going on.

 

[that-guy]

AL feeders are the way to go unless u have money to blow on cu.

As pattenp said, the only potential issue is insulation failure. This can be mitigated by use of conduit for the underground run.

How long of a wire run are we talking?

If u truly need and want 100a in the garage, u will need a minimum of #1 AL. #2 AL is only good upto 90a in this application.

I haven't taken an exact measurement, but I am guesstimating 50-75 feet, probably 40 to be buried 18" down in conduit.

by a chart I found, #2 aluminum THHN is good to 100a...I was thinking I could run 2/2/2/4, assuming the 4 will be for the ground

 

[CNGsaves]

What Country are you in ??? Update GJ Profile with location.

GJ Sparkies above have got you on right track with cheapest/best solution which is MHF (mobile home feeder) aluminum 2-2-2-4 which is around $1.50/ft. Run 2" conduit end-to-end and you'll have lifetime solution.

You will need to limit the breaker in house to 90A feeding the MHF Al 2-2-2-4 to garage.

 

[that-guy]

What Country are you in ??? Update GJ Profile with location.

GJ Sparkies above have got you on right track with cheapest/best solution which is MHF (mobile home feeder) aluminum 2-2-2-4 which is around $1.50/ft. Run 2" conduit end-to-end and you'll have lifetime solution.

that's exactly what I was looking into, but wanted to make sure that it is what I need for my application. so am I right in assuming that two 2's are my hot, third 2 is my neutral, and 4 is my ground?

 

[pattenp]

#2 aluminum is good to 90A @ 75 deg C as a branch feeder per NEC.

 

[pattenp]

that's exactly what I was looking into, but wanted to make sure that it is what I need for my application. so am I right in assuming that two 2's are my hot, third 2 is my neutral, and 4 is my ground?

Correct.

 

[Norcal]

Copper is the conductor of choice, AL is cheaper, but either installed incorrectly will cause problems.

 

[CNGsaves]

Post up PICs of your main panel in house (panel on / panel off) along with subpanel in garage, and the GJ Sparkies will give you best advice on what they observe. They will need your Country location as rules vary a bit country-to-country.

 

[justsam]

You mention THHN, which is wire, i.e. individual conductors. You will want THWN for wet location. The MHF (Mobile Home Feeder) mentioned is a cable with all 4 conductors molded together.

Either way will get you there, the MHF may be cheaper.

I suspect all would use copper as opposed to AL unless weight is a factor, but at some point the cost is not justified. There is a reason there are copper thieves but no AL thieves.

 

[Speedy Petey]

You mention THHN, which is wire, i.e. individual conductors. You will want THWN for wet location.

I see this mentioned CONSTANTLY, and while it is true I have yet to see a modern (within the past maybe 15-20 years) THHN conductor that is not dual rated THHN/THWN.

 

[that-guy]

I am located in Virginia. this is exactly what I am referring to:

http://www.lowes.com/pd_70203-295-13102915_1z0v13t__?productId=4294349&pl=1

 

[brewchief]

That is SER cable and cannot be run underground.

Sent from my XT1254 using Tapatalk

 

[Speedy Petey]

I am located in Virginia. this is exactly what I am referring to:

http://www.lowes.com/pd_70203-295-13102915_1z0v13t__?productId=4294349&pl=1

That is Type SE cable and CANNOT be used underground.

You need URD or MHF cable.

 

[that-guy]

I never read anything about that...what is the reasoning for not being able to bury this under ground with conduit?

 

[yaidunno]

I never read anything about that...what is the reasoning for not being able to bury this under ground with conduit?

Quoted from an electrical forum:

"Since any raceway underground is by definition a wet location, and the equipment ground wire in SER cable is a bare conductor, it is subject to corrosive locations, and is also a bare conductor in earth, even though it is in a raceway. The outer jacket of the cable is not an insulation, it is a covering and thus cannot be used as an insulated conductor underground.
The same rules apply to SEU since the neutral is a bare aluminum conductor. "

I was just as disappointed as you are to find that SER is not underground rated. I wanted the full 100A service to my shop, and did not want to deal with pulling 1/0 AL, so i went with #2 CU THHN/THWN wire, and have no regrets. 150' run of wire in my application, so I bumped up the wire size from #1 AL or #3 CU, which is normally used for 100A service.

 

[theoldwizard1]

I never read anything about that...what is the reasoning for not being able to bury this under ground with conduit?

Because the National Electric Code said so ! It really does not matter. Likely the insulation is not water resistant.

This what you want MHF

MHF MUST be run in conduit anywhere it is above ground. Do yourself a favor and use a Schedule 80 "sweep" when coming out of the ground and up to you LB. Weed whips can break a Schedule 40 conduit.

 

[pattenp]

Since URD was mentioned. One important note about URD is that it is not allowed inside the structure and must be terminated outside. The reason is URD does not have a fire resistant rated insulation. MHF can be installed inside because it does have a fire resistant insulation. But as said, MHF needs to be in conduit where exposed above ground and where installed inside the structure.

 

[wyliesdiesels]

I never read anything about that...what is the reasoning for not being able to bury this under ground with conduit?

Since the EGC is bare, if water ever gets inside the jacket(which isnt insulation) the bare aluminum ground wire will turn into a mushy substance.

 

[Slowgsr]

I just picked up a cable for a job im going to on Sunday,

57m of 2/3 teck 90, and of course its copper.
I'll get my mini loaded up Saturday after work, should just in time before the ground freezes.

I only run copper, reason being 90% of my work is enginerred, and for some reason they always spec copper. Unfortunately sometimes I get stuck bidding against guys who sneak in Al.

Is it better? Yes in every way other then cost. So do I think it's worth it? Probably, my shop has 3/3 copper, and my spa has 6/3 copper.

For guys doing work themselves who aren't paying labor, I'd go aluminum. Since you've probably got the dollar on your mind anyways.

 

[My Old Tools]

2-2-2-4 MHF and a 90 amp breaker and your in business. Lowes carries it here. Minimum of 2" conduit, bigger doesn't hurt if you have many bends.

 

[Crazyjake8493]

2-2-2-4 MHF and a 90 amp breaker and your in business. Lowes carries it here. Minimum of 2" conduit, bigger doesn't hurt if you have many bends.

I think 1 1/2" is the minimum size conduit for MHF, but 2" would make it a bit easier.

Also, Lowes may not have the breaker in the store but they can order it. Around here, the big box stores only carry breakers up to 60a, and a 100a for each line of panels. They all carry 70a and 90a breakers online.

 

[MikeF2316]

This has no bearing on anything but my prejudices. And I'm sure a few others share these. My dad was always against aluminum wiring back in the '60s and '70s when they were wiring houses with it. And it turns out he was right, considering all the problems. No way no how was anything that he did going to have aluminum wire. (He was not an electrician.) I was young and impressionable during that time, so a couple of years ago when I upgraded my detached garage from 12/3 (20 amps) to 6/3 (60 amps) aluminum didn't even enter my calculations no matter how much cheaper it was. The electrician I hired thought the same way, and he was a relatively young guy. Teck90 was pretty much all he used.

 

[wyliesdiesels]

Al wire has come along ways over the decades.

Todays Al is different than the infamous fire prone stuff of the 60s and 70s

http://www.southwire.com/commercial/ALBuildingWire30YrsOfReliability.htm

 

[Norcal]

Today's aluminum alloy, and the aluminum of the past are light years apart, for feeders aluminum alloy conductors are a legitimate way to reduce costs.

 

[tfi racing]

Well if people want to throw extra cash at copper feeders for no valid reason,who are we to convince them otherwise?They can be smug and sleep well at night with the satisfaction of money well wasted,I'm just gonna buy more beer with the cash I saved and be smug and satisfied with that instead...

 

[that-guy]

the weather finally let up for me last night, so I got outside to measure how much service cable I will need, and I came up with roughly 80 feet. looking more and more into this, it seems that certain size cable will only carry the load up to a certain distance

so my new question is, for an 80 foot run, what size cable do I need to run, in aluminum, for a 100amp service?

for those who respond, please provide literature, etc. for your findings

 

[404]

Well if people want to throw extra cash at copper feeders for no valid reason,who are we to convince them otherwise?They can be smug and sleep well at night with the satisfaction of money well wasted,I'm just gonna buy more beer with the cash I saved and be smug and satisfied with that instead...

Yes, but in 20 minutes the beer will be gone, and next day that smugness as well. Then one has to get more beer thus spending more money. So in the long run it is better and cheaper to use copper and have the smugness last forever.

 

[My Old Tools]

the weather finally let up for me last night, so I got outside to measure how much service cable I will need, and I came up with roughly 80 feet. looking more and more into this, it seems that certain size cable will only carry the load up to a certain distance

so my new question is, for an 80 foot run, what size cable do I need to run, in aluminum, for a 100amp service?

for those who respond, please provide literature, etc. for your findings

Drop down to a 90 amp breaker and run 2-2-2-4 MHF. If you stay at 100 amps you'll need to upsize. You can still use a 100 amp panel, just feed it with a 90 amp breaker.

 

[myredracer]

The problem with aluminum in the 60s & 70s was with #14 & #12 branch circuit wiring not larger feeder sizes. Alum. is used on commercial jobs all the time without problems as long as the correct installation procedures are followed like using Noalox anti-oxidizing paste, using wire stripper, keeping min. bending radius when pulling and correct tightening of lugs (required torque), etc. I used to spec. on projects that aluminum could only be used on 200 amp conductors and larger. Not sure what the NEC allows for min. alum. sizes.

For 100 amp feeder, you should be able to get that in 1" conduit which can make it much easier to connect to a box or enclosure. If you need larger than 1" conduit, you might price out 2" DBII thinwall conduit for use underground. It may be cheaper but you'd probably need a pull box or two at either end to reduce to smaller conduit before going into a panel and you may need to bed it in a sand layer.

If you have larger motor loads in the shop, you may want to think about increasing the wire size another gauge or two to reduce voltage drop on startup. Motors momentarily draw 6 times their FLA and excessive voltage drop can be hard on some motors and cause annoying lighting flicker.

I would not hesitate to use alum., either indoors or below grade. The usual rule of thumb is that it needs to be one wire gauge heavier as compared to copper (refer to NEC for exact requirement). With fatter wire, it will often force you into a larger dia. conduit (NEC "conduit fill") and that should be factored into a price comparison. Fatter wire can be harder to pull through conduit but for the size and distance in question, probably not an issue. Keep conduit bends to a min. (max. 4 between pulling points) and use lube when pulling.

For someone to nick the insulation badly enough to allow water to contact the conductors, they'd have to be pretty negligent. I've never heard of this happening. Insulation is pretty tough stuff.

I installed parallel 200 amp rated aluminum conductors in 2" DBII conduit with about 200' overall length in the last house I built. I built a custom sized concrete pullbox outside the house to allow for pulling upwards vertically. Used lots of lube and pulled hard with a friend's help and no problem. (When with a parallel feeder to reduce voltage drop.) 100 amp wire at 50 - 75' would be easy peasy. If you can find a cable like teck or similar for a good price and it can be direct buried, that would simply things.

 

[that-guy]

Thank you for that Gil-...I don't believe I have anything that will make a large enough start up draw that I should be concerned about voltage drop. this is a one man shop where no more than a few things could possibly be running at once. and I have already planned out my route for my feed line, and it will only have one bend where it comes out of the ground and into the building, and I am using a pre-bent 90* piece of conduit for that

in your opinion, would you say that what "My Old Tools" said is fairly accurate?

 

[Norcal]

AL branch circuits were always 12 AWG for 15A, & 10 AWG for 20A, 14 AWG was never used, except when reduced equipment grounding conductors were permitted which went away in either the 1968 or 1971 NEC.

 

[My Old Tools]

Do not try to get 2-2-2-4 AL into 1" conduit. DAMHIKT. 1.5" will work, 2" is easier if you have many bends to pull through. I used plastic for my underground feed.

 

[newfie]

Aluminum when used as a wire with current flowing will heat up and expand. Over time this will cause the connection to become loose. This is called "cold flow". In Canada we used AL wire in houses for a few years until the cold flow was creating a high point of resistance in the connection. With high resistance and constant current we burnt a bunch of houses down with improper connections and not re torquing the lugs. Copper will expand less and is by far the best choice.

 

[dslabuda]

Well if people want to throw extra cash at copper feeders for no valid reason,who are we to convince them otherwise?They can be smug and sleep well at night with the satisfaction of money well wasted,I'm just gonna buy more beer with the cash I saved and be smug and satisfied with that instead...

Some people use the same argument for chicom vs USA made.

 

[pattenp]

Aluminum when used as a wire with current flowing will heat up and expand. Over time this will cause the connection to become loose. This is called "cold flow". In Canada we used AL wire in houses for a few years until the cold flow was creating a high point of resistance in the connection. With high resistance and constant current we burnt a bunch of houses down with improper connections and not re torquing the lugs. Copper will expand less and is by far the best choice.

That issue was with old style aluminum wire back in the 60's and 70's. New aluminum alloy used today in larger feeder/service wire does not have that problem and is safe and does not require re-torquing if installed correctly in the first place. Inferring that the old history of aluminum wire as being applicable with today's newer aluminum wire is incorrect.