Aluminum vs Copper

[snturner]

I am adding a sub-panel to a detached garage. I have 300 amp service in the house ( two boxes ). One of the boxes ( 200 amp ) has a jacuzzi tub on it, and that's it. I plan to use a 100 amp breaker from that box to supply the sub-panel.

The detached garage will be used as a woodworking shop, with a 220 table saw. Everything else will be 110. The only other electricity hog will be a window unit A/C. Probably a small electrical heater in the winter. The garage is only 20 X 22.

My question is: What are the pros and cons of aluminum vs cooper for the feeder cable from the house to the sub-panel? Will I be fine using aluminum? If I choose cooper I plan to use 4 ga. If I use aluminum, I will use 00 ga. I will use copper for all lights and receptacles.

The reason I ask is the aluminum is about half the cost. I understand the differneces of copper and aluminum as far as amps, heat and expanding wire. But the house is feed with aluminum wire. What would keep me from feeding a sub-panel 100 ft away with aluminum?

 

[browntown]

Re: Aluminum vs Cooper

Interested in the answer as well. My eyes bulge when I see the price of copper wire these days.

 

[Firestarter]

Re: Aluminum vs Cooper

Aluminum can be used for main service entrance and sub panels.

 

[snorky18]

Re: Aluminum vs Cooper

Aluminum Pros:
Cheap
Works
As Firestarter said, fine for sub panels.

Aluminum Cons:
Larger conductors for the equivalent ampacity as copper.
Can be very difficult to bend SER (typical subpanel cable) in anything but a very large radius b/c it is 3-4 very large wires bound together.
Also maked working in a very crowded panel much more difficult b/c of the size of wires and bend radius required.
Known for problems in wiring from the olden days, but IIRC that was branch circuits.

Copper Pros:
Smaller Wire Size-easier to work with

Copper Cons
The hole in your pocketbook.

If you use AL, look into Noalox.

 

[pattenp]

Re: Aluminum vs Cooper

Are you in the US? If so use aluminum(AL). You need to use 1/0 AL for 100A. I recommend Mobile home feeder but I don't think it comes in 1/0, you would need to get 2/0-2/0-2/0-1.
See this link: http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet15

And #4 copper(CU) is not large enough for 100A, you need to use at a minimum #2 CU.

Be sure to use aluminum antioxidant paste on all of your connections when using AL wire.

Also, I think 100A service to your shop may not be needed. I think you'd find that 60A will work fine and will cost less. I have 60A to my garage and run everything you are looking at plus I have a car lift, 240V compressor and etc. and never have tripped the 60A breaker. If you use AL HMF 2/2/2/4 you can breaker it up to 75A.

 

[ishiboo]

Re: Aluminum vs Cooper

Are you in the US? If so use aluminum(AL). You need to use 1/0 AL for 100A. I recommend Mobile home feeder but I don't think it comes in 1/0, you would need to get 2/0-2/0-2/0-1.
See this link: http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet15

And #4 copper(CU) is not large enough for 100A, you need to use at a minimum #2 CU.

Be sure to use aluminum antioxidant paste on all of your connections when using AL wire.

Also, I think 100A service to your shop may not be needed. I think you'd find that 60A will work fine and will cost less. I have 60A to my garage and run everything you are looking at plus I have a car lift, 240V compressor and etc. and never have tripped the 60A breaker. If you use AL HMF 2/2/2/4 you can breaker it up to 75A.

Agreed.

Aluminum is the standard for service entrance installations here, and has been for quite some time. It is much safer than the old aluminum installs right to the devices and wire nuts, which were prone to issues. I wouldn't run copper even if I got it for free - I'd sell the scrap and buy Aluminum - unless I had an exceptional reason

 

[PRH44]

Re: Aluminum vs Cooper

Your garage is detached so you will need to run a 4 wire conductor arrangement. 2 phase conductors 1 neutral and a ground conductor. If you plan on using USE (underground service entrance cable) cable or “Mobil home feeder cable” For 100 amps you will need to use at least a #2 ( permitted to be on a 100 amp breaker per NEC 240.4(b) and 240.6) or #1 copper. For aluminum 1/0 or larger is fine. This is based on 2011 NEC 310.15(B)(16) using the 60 degree column.
The distance of 100 feet will not give you a significant voltage drop. 1/0 Aluminum at a load of 80 amps at 240 volt will net you less than a 1.62% voltage drop.

Copper is a better conductor than aluminum always has, always will . It does not suffer from creep or oxidize as readily as Aluminum. However with the rising cost of copper aluminum has become the material of choice when economics are considered. It is a fine conductor when used in large sizes such as #1 and larger. It is used commercially as feeder conductors more often than copper these days. The new compact stranding has reduced creep greatly. So to answer your question as a feeder Aluminum is fine. My opinion is never use aluminum for smaller branch circuits use copper as you stated.

There are a few things you need to keep in mind when installing aluminum.
1. Use lugs that are rated for aluminum most load centers today have dual rated lugs for copper or aluminum. Dissimilar metals can cause galvanic reactions.
2. Try your best to not nick or ring the aluminum conductor when stripping the insulation.
3. When terminating coat the entire exposed surface of the conductor with an anti-oxidant compound such as Noalox. A small brush works fine for this. This will prevent
4. Lug information such as torque can normally be found on the breaker or on the label of the panel. Use a torque wrench to set the lugs to the proper torque.
This will give you many years of trouble free current flow.

 

[Teken]

Re: Aluminum vs Cooper

Your garage is detached so you will need to run a 4 wire conductor arrangement. 2 phase conductors 1 neutral and a ground conductor. If you plan on using USE (underground service entrance cable) cable or “Mobil home feeder cable” For 100 amps you will need to use at least a #2 ( permitted to be on a 100 amp breaker per NEC 240.4(b) and 240.6) or #1 copper. For aluminum 1/0 or larger is fine. This is based on 2011 NEC 310.15(B)(16) using the 60 degree column.
The distance of 100 feet will not give you a significant voltage drop. 1/0 Aluminum at a load of 80 amps at 240 volt will net you less than a 1.62% voltage drop.

Copper is a better conductor than aluminum always has, always will . It does not suffer from creep or oxidize as readily as Aluminum. However with the rising cost of copper aluminum has become the material of choice when economics are considered. It is a fine conductor when used in large sizes such as #1 and larger. It is used commercially as feeder conductors more often than copper these days. The new compact stranding has reduced creep greatly. So to answer your question as a feeder Aluminum is fine. My opinion is never use aluminum for smaller branch circuits use copper as you stated.

There are a few things you need to keep in mind when installing aluminum.
1. Use lugs that are rated for aluminum most load centers today have dual rated lugs for copper or aluminum. Dissimilar metals can cause galvanic reactions.
2. Try your best to not nick or ring the aluminum conductor when stripping the insulation.
3. When terminating coat the entire exposed surface of the conductor with an anti-oxidant compound such as Noalox. A small brush works fine for this. This will prevent
4. Lug information such as torque can normally be found on the breaker or on the label of the panel. Use a torque wrench to set the lugs to the proper torque.
This will give you many years of trouble free current flow.

Please define and describe *creep* to those not in the know.

Teken . . .

 

[Falcon67]

Re: Aluminum vs Cooper

I used 2/2/2/4 aluminum cable for my shop feed. It's a little under 100' and I fused it at 70A because that breaker size was handy. I figure if I trip 70A, I really got it going on. Or, there's a short. My shop is 960 sq/ft with electric heat and two AC units, plus a ton of power equipment.

 

[PRH44]

Re: Aluminum vs Cooper

A few other things you need to consider when installing electrical service to detached garages.
You will be required to provide means of disconnect at the garage per NEC 225.31 The disconnecting means shall be at a readily
accessible location nearest the point of entrance of the conductors.
This can be in the form of one of the following options:
1. Use a MLO (main lug only) load center. Install no more than 6 breakers in the panel. NEC 225.33
2. Install a separate disconnect switch outside or inside ahead of the MLO panel.
3. My preferred method. Use a main breaker load center. Load centers can be purchased with mains and a few breakers packaged together at an affordable price.
The subpanel in the detached garage you will Terminate the neutral on an insulated neutral bus only. Terminate the ground to a ground bus, do not bond then together.

 

[pattenp]

Re: Aluminum vs Cooper

Aluminum wire creep is the expansion and contraction that caused AL wire to be problems when used in branch circuits supplying devices such as outlets, lights, etc. Connections would become loose.

 

[Teken]

Re: Aluminum vs Cooper

Aluminum wire creep is the expansion and contraction that caused AL wire to be problems when used in branch circuits supplying devices such as outlets, lights, etc. Connections would become loose.

Thank you for the clarification. I was not aware of this phrase as it pertains to Aluminum wiring.

Teken . . .

 

[PRH44]

Re: Aluminum vs Cooper

Please define and describe *creep* to those not in the know.

Teken . . .

CREEP (COLD FLOW)
Creep is the cold flow of the metal under
pressure, and it continues until the pressure
reduces to a value at which any further creep
is negligible. Creep properties depend on the
particular metal or alloy and on its hardness;
alloys having less creep than pure metals,
and harder metals have less creep than soft
metals. In a typical connection, the conductors
are generally of pure metal and often of
soft temper and therefore, subject to considerable
creep. In addition, the condition is
further exaggerated when aluminum is the
conductor as compared to copper, since its
creep rate is many times that of copper

This is from Burndy

 

[PRH44]

Creep has been lessened notably by the advent of compact stranding. Aluminum strands were originally round creating air space between them. This would increase the creep affect, as well as air pockets that would aid in oxidation.
Compact stranding created a more flat or hexagonal shape filling the voids making the conductor smaller and more “compact”.
The once present gaps no longer aid in creep and oxidation.

 

[Teken]

Creep has been lessened notably by the advent of compact stranding. Aluminum strands were originally round creating air space between them. This would increase the creep affect, as well as air pockets that would aid in oxidation.
Compact stranding created a more flat or hexagonal shape filling the voids making the conductor smaller and more “compact”.
The once present gaps no longer aid in creep and oxidation.

Most excellent! I find it interesting that this technique / technology is not being used more often in more wiring industries? I have to gather it is direct cost to manufacture the cable in this manner.

Impressive to say the least . . .

Teken . . .

 

[PRH44]

Aluminum is sold almost exclusive as compact stranding anymore. There are motivations for the manufacture to produce compact stranding as will elaborate. Copper is available but not as readily available

 

[PRH44]

The Aluminum conductor in the larger compact stranded form have come a long way. Although it will always be inferior to copper in its ability to carry current as it takes more mass, it has it has its place. In today’s market it is extremely more affordable than copper.
Used often as feeders and service entrance conductors in the residential market.
Its greatest contribution is in the Commercial and light industrial markets. Where once conduit sizes needed to be increased substantially to use aluminum, there for driving job cost up. Coupled with the age old maintenance issues attributed to creep and oxidation. Aluminum conductors were less attractive. Compact stranding has improved this dramatically allowing smaller conduit ( and lugs as I can explain in another post.) Driving the cost of large scale projects down making them more affordable for the owner. The fact aluminum is just plain cheaper that copper is one aspect.

The aluminum salesmen now like to state you do not need to increase conduit size over copper at all if you use compact stranding. Well……. this is true to some degree.

 

[snturner]

Thank you for all the information. One thing that stands out to me about my plans is 100 amps is over kill. Probably go down to 70 or 75 which ever is more common. I know I am going to be upset if I every expand in the near future and don't have enough. But 70 amp sounds like it will be good for me. I am thinking the most I would ever have running at one time would be 35 to 40 amps, tops.

All the information on the aluminum tells me I won't have any issues using it.

Thanks, the information is greatly appreciated.

 

[ishiboo]

Thank you for all the information. One thing that stands out to me about my plans is 100 amps is over kill. Probably go down to 70 or 75 which ever is more common. I know I am going to be upset if I every expand in the near future and don't have enough. But 70 amp sounds like it will be good for me. I am thinking the most I would ever have running at one time would be 35 to 40 amps, tops.

All the information on the aluminum tells me I won't have any issues using it.

Thanks, the information is greatly appreciated.

Id run 100... 100A is a VERY common service size so the wire is cheap and available everywhere. For the minimal if any cost increase of running the wire, I'd rather be protected down the road if I ever missed that 30A

 

[PRH44]

I would agree with ishiboo

 

[pattenp]

To go 100A vs. 70A is not a lot of money. My guess would be $75 more. The main thing is going to be working with the larger wire for 100A, harder to pull and harder to terminate in the box, not a big deal, just needs a little more effort.

 

[Aceman]

Re: Aluminum vs Cooper

If you plan on using USE (underground service entrance cable) cable or “Mobil home feeder cable” For 100 amps you will need to use at least a #2 ( permitted to be on a 100 amp breaker per NEC 240.4(b) and 240.6) or #1 copper. For aluminum 1/0 or larger is fine. This is based on 2011 NEC 310.15(B)(16) using the 60 degree column.

I see the articles you posted but I still don't see how you are coming up with your ampacities and breaker sizes.

Mobile home feeder is rated RHH/RHW/USE-2, so it's taken straight from the 75 degree column.

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet15

#2 AL is 90 amps. 90 amp breaker max.
1/0 AL is 120 amps. 125 amp breaker max.
#1 CU is 130 amps. 125 breaker max.

 

[pattenp]

Re: Aluminum vs Cooper

2011 NEC 338.10(B)(4)(b) for USE requires compliance with 340.80 which states you have to use the 60C conductors in 310.15.

There are different requirements when SE and USE are used in branch/feeder circuits vs. when used as the main service entrance from the meter base to the main panel.

See foot notes at bottom of chart for 60C. This NEC 2008 reference http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet12

I see the articles you posted but I still don't see how you are coming up with your ampacities and breaker sizes.

Mobile home feeder is rated RHH/RHW/USE-2, so it's taken straight from the 75 degree column.

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet15

#2 AL is 90 amps. 90 amp breaker max.
1/0 AL is 120 amps. 125 amp breaker max.
#1 CU is 130 amps. 125 breaker max.

 

[PRH44]

Re: Aluminum vs Cooper

I see the articles you posted but I still don't see how you are coming up with your ampacities and breaker sizes.

Mobile home feeder is rated RHH/RHW/USE-2, so it's taken straight from the 75 degree column.

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet15

#2 AL is 90 amps. 90 amp breaker max.
1/0 AL is 120 amps. 125 amp breaker max.
#1 CU is 130 amps. 125 breaker max.

the reference is #2 ( permitted to be on a 100 amp breaker per NEC 240.4(b) and 240.6) or #1 copper. both references to #2 and #1 are for copper 95 and 110 respectively at 60 degrees.

1/0 USE AL cable at 60 degrees is 100 amps

 

[Aceman]

Re: Aluminum vs Cooper

2011 NEC 338.10(B)(4)(b) for USE requires compliance with 340.80 which states you have to use the 60C conductors in 310.15.

There are different requirements when SE and USE are used in branch/feeder circuits vs. when used as the main service entrance from the meter base to the main panel.

See foot notes at bottom of chart for 60C. This NEC 2008 reference http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet12

I'd buy that if this was straight rated USE, because they do make it, but this is not it. It's rated RHH/RHW as well, which bumps it to the 75 degree column.

 

[Aceman]

Re: Aluminum vs Cooper

the reference is #2 ( permitted to be on a 100 amp breaker per NEC 240.4(b) and 240.6) or #1 copper. both references to #1 and #2 are for copper 95 and 110 respectively at 60 degrees.

Where will the OP find a 60 degree wet location cable with #2 or #1 copper in it?

 

[pattenp]

Re: Aluminum vs Cooper

I'd buy that if this was straight rated USE, because they do make it, but this is not it. It's rated RHH/RHW as well, which bumps it to the 75 degree column.

Where in the NEC does it allow an exception to the 60 degree requirement because of being RHH/RHW. The code in article 338 and 340 are blanket in coverage of SE and USE to me regardless of the make up of the conductors in the cable.

Also SE and USE as to article 338 are cable types not conductor types. RHH/RHW/USE-2 are conductor types, can be used to make up USE.
Plus USE is being used with two meanings, one as a multiwire cable and also as a conductor type which adds to the confusion.
We also may be talking pass each other. The 60 degree requirement is for when buried or run inside of insulation. If in free air then 75 degree is used.

 

[Provincial]

I always figure that the amp rating of the circuit should be as high as practical for a shop because motor starting loads produce high current flows for short durations. While the breaker might not trip, you will experience a voltage drop if the wire size is not larger than the minimum required for the normal running (full-load) amperage. Thus, going to 2/0 wire when 1/0 is allowed by the code is not wasteful if you start larger motors.

If you will never have larger motors in the shop, it does not matter, but someone may wish for more capacity later. Wire, while expensive, is pretty cheap compared to a do-over.

 

[PRH44]

As reguested copper USE cable.

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet7

 

[dgkrzy]

I would suggest a 100 amp w/aluminum conductors. If you look around you should be able to find a 100 amp valu-pack. Which is a panel packaged with several breakers (usually single pole 20 and 15 amp breakers and a double pole 30 amp). You may find that the 100 amp combination is cheaper than 70 amps because the 100 amp equipment/breaker is more readily available. It may be allowed by your inspector to use a lug kit in the main panel (rather than a breaker) and feed the 100 amp breaker in your garage panel, thus saving money by not needing 2 100 amp breakers.
You will need to run 4 conductors (2 hot / 1 neutral / 1 ground) and provide grounding electrodes (rods/plates/or reinforcing steel) at the garage.

Conductor ampacity can be found in NEC 310.15 (B)(16). There is a special table NEC 310.15 (B)(7) but that is only valid for the main service conductors, not conductors to a sub panel.

According to Table 310.15(B)(16), a 1/0 AL USE has an ampacity of 100 amps in the 60 degree column.

If you are going underground, you should try to order 1/0 URD quad (underground residential distribution / 4 conductor) for this, because it will be easy to use (already bundled and twisted so pulling it in conduit is easier), and should be readily available at any electrical supply house.

URD is listed for direct burial (no conduit required) but unless you have really clean fill I would recommend conduit, 1 1/2" is larger than absolutely needed but would be easier to work with than 1 1/4". Where the wire emerges from the ground it will need to be protected by Schedule 80 PVC conduit or metal conduit. The additional benefit of using conduit is that it will reduce the minimum cover depth (how deep you have to dig) to 18" vs. 24" for direct bury wire.

 

[pattenp]

I disagree with the bold statement below because NEC article 338 and 340 require USE to be calculated from the 60 degree column. The device temp rating does not come in to play.

................

According to Table 310.15(B)(16), a 1/0 AL USE has an ampacity of 100 amps in the 60 degree column. If all parts of your circuit (breakers & lugs) are rated for 75 degrees, you could go as small as #1 AL USE, but I have never used that size wire in aluminum so I don't know how common it is.
...................

 

[PRH44]

I disagree with the bold statement below because NEC article 338 and 340 require USE to be calculated from the 60 degree column. The device temp rating does not come in to play.

Agree with pattenp

 

[dgkrzy]

NEC 338.10 (4) restricts the wire to the 60 degree rating for interior installations with thermal insulation, and although part of this circuit is inside, the majority of it is exterior. I think this is a code interpretation issue
The explanation in the NEC Handbook does refer to 110.14 for device temp ratings if thermal insulation is not a factor

 

[dgkrzy]

I interpret "installation in thermal insulation" to mean fiberglass or some other type of insulation used to prevent heat loss within the dwelling

 

[pattenp]

I interpret "installation in thermal insulation" to mean fiberglass or some other type of insulation used to prevent heat loss within the dwelling

Read post #23. I'm using 2011 NEC and talking about the USE not SE. USE can not be installed inside. SE installed in free air not in insulation can be calculated from the 75 degree column.

 

[Falcon67]

Thank you for all the information. One thing that stands out to me about my plans is 100 amps is over kill. Probably go down to 70 or 75 which ever is more common. I know I am going to be upset if I every expand in the near future and don't have enough. But 70 amp sounds like it will be good for me. I am thinking the most I would ever have running at one time would be 35 to 40 amps, tops.

All the information on the aluminum tells me I won't have any issues using it.

Thanks, the information is greatly appreciated.

I did a test on my old shop - 14 4 foot lights, drill press, 5kW heater, 240V 3.5hp air compressor, lathe, mill, bench grinder, belt sander all running at once. The clamp meter peaked at 49A

 

[dgkrzy]

I am also referring to the 2011 edition - I interpret this restriction to mean that if the cable or conductors are routed through an interior area that has thermal insulation (ie: fiberglass), then the ampacity of the conductors is limited to those listed in the 60 degree column. Otherwise, they would be restricted by the component of the circuit with the lowest temperature rating.
In other words if I were to pull the wire through an insulated ceiling I would be limited to the ampacity in the 60 degree column, but if the ceiling were uninsulated I would not necessarily be limited to the 60 degree column if all parts of the circuit were of the same rating.

This is probably way more involved/technical than the OP expected.

 

[pattenp]

You are correct about the 60 degree requirement for inside in insulation or in free air. This would apply to SE cable. I'm talking about service feeds under ground (USE) which you have to use the 60 degree column. USE can not be used for interior wiring.

I am also referring to the 2011 edition - I interpret this restriction to mean that if the cable or conductors are routed through an interior area that has thermal insulation (ie: fiberglass), then the ampacity of the conductors is limited to those listed in the 60 degree column. Otherwise, they would be restricted by the component of the circuit with the lowest temperature rating.
In other words if I were to pull the wire through an insulated ceiling I would be limited to the ampacity in the 60 degree column, but if the ceiling were uninsulated I would not necessarily be limited to the 60 degree column if all parts of the circuit were of the same rating.

This is probably way more involved/technical than the OP expected.

 

[dgkrzy]

I assumed the OP was talking about an outdoor installation as his distance listed was 100' +/-.
I understand your point, so I don't see why you would disagree with my original statement, the USE is not allowed to be installed indoors, so it would not be in thermal insulation, therefore the ampacity is only limited by the 'weakest link' of the chain, not the specific statement in NEC 338.10 (B)(4).

 

[Falcon67]

In other words if I were to pull the wire through an insulated ceiling I would be limited to the ampacity in the 60 degree column, but if the ceiling were uninsulated I would not necessarily be limited to the 60 degree column if all parts of the circuit were of the same rating.

And that makes no sense at all, from a practical perspective. I ran my cable through an insulated attic - and the cable is not in the insulation, it is kept off it. Deliberately. So you are required to de-rate the cable because insulation happens to be close by. Do what?? If it was buried it it - sure. But just because insulation is present - thats a poor engineering basis, IMHO.

Also - just for fun - two local masters AND the inspector all said "100 amp" when I said "2-2-2-4 aluminum". I 'splained fully the run, length, cable, conduit size, etc - all said "meets code". Utility engineer - same thing. I could put a 100A breaker on the run and nobody would say boo about it. I enjoy the technical discussions - just seems that locally, whats really OK may be a little different for local reasons.