[crote]

With regards to the copper market: it keeps surprising me that some people seem to assume copper is a hard requirement for conducting electricity.

In reality copper is just convenient. We use it because it's easy to work with, a great conductor, and (until recently) quite affordable. But for most applications there's no reason we couldn't use something else!

For example, a 1.5mm2 copper conductor is 0.0134kg/m, which at current prices is $0.17 / meter. A 2.4mm2 aluminum conductor has the same resistance, weighs 0.0065kg/m, which at current prices is $0.0195 / meter!

Sure, aluminum is a pain to work with, but with a price premium like that there's a massive incentive to find a way to make it work.

Copper can't get too expensive simply due to power demands because people will just switch to aluminum. The power grid itself had been using it for decades, after all - some internal datacenter busbars should be doable as well.

[dzink]

You just have to not mix and match. If you mix them the two need special bonding at every single connector or they can cause arching and fires.

[amluto]

If by “special” you mean ordinary low-cost lugs, then sure.

Check it out:

https://lugsdirect.com/WhyAluminumOverCopperFAQ.htm

And you can browse that site for lugs, and they’re mostly rated for aluminum and copper. Copper-only lugs are actually rather unusual.

Sure, you can’t stick copper and aluminum wires into a wire nut, and finding terminations for smaller-gauge aluminum wire can be hard. But for larger wire, it’s really no problem.

[quickthrowman]

Most wiring device terminations and lugs are Al/Cu rated. You’re supposed to use specific fittings for splicing together aluminum and copper wire (specific WAGO lever nuts are UL listed for this purpose along with some others), I assume that’s what you meant.

[y-curious]

I am not an electricity/wiring guy so maybe you can help me understand. I thought aluminum is dangerous to wire with because it is a fire hazard (I bought a home this year and this was a prominent warning in my reading). Is that because it needs to be done very carefully? I imagine most data centers would not mess with a fire risk on such a scale.

[crote]

That's the "a pain to work with" part.

Residential aluminum is a Really Bad Idea because DIY Dave will inevitably do something wrong - which then leads to a fire hazard. Copper is a lot more forgiving.

But a large scale datacenter, solar farm, or battery storage installation? Those will be installed and maintained by trained electricians, which means they actually know what a "torque wrench" is, and how to deal with scary words like "corrosion" and "oxidation".

Like I said: it's what's used for most of the power grid. With the right training it really isn't a big deal.

[jabl]

Aluminum got a bad rep due to a lot of poor installations made in the 1960 and 70'ies. Subsequently new alloys (AA-8000 series) for wiring, new installation and termination procedures etc. have been developed, and AFAIU the situation today is much better. It's still trickier than copper wiring, so probably not a good option for DIY, but for some industrial installation with competent personnel and where the savings can be substantial it could certainly be an attractive option.

https://en.wikipedia.org/wiki/Aluminum_building_wiring

[scherlock]

Aluminum oxide has high resistance and if you mix aluminum wiring with copper outlets, etc the impedance mismatched is what causes fires. You need to either have special copper pigtails installed or use fixtures that are rated for aluminum wiring.

For commercial installs, it shouldn't be a problem as long as it's planned for.

[auxym]

It's because aluminium has a higher coefficient of thermal expansion. It expands and shrinks more as it heats, and as those cycles add up it tends to loosen electrical connections. Loose connections have higher resistance, heat up and can cause fires.

That said, there is no reason we can't design better connectors that can withstand the expansion and shrinkage cycles, like spring loaded or spring cage connectors.

[quickthrowman]

Wiring devices have almost all been universally rated for Al/Cu conductors for the last 50 years, what you’re talking about only lasted a handful of years in the early 1970s.

Go look at the terminals on any light switch or receptacle at Home Depot, they’re all Al/Cu rated.

[_heimdall]

Unless I'm mistaken, the risk with aluminum is that it can expand and contract if it gets too hot. Aluminum sized properly with the correct connectors torqued to spec would be fine, aluminum wires in a residence with a DIYer working on it can be riskier and is why inspectors will always note it.

[u8080]

Aluminum wires became brittle over time(tens of years), fluid which requires some maintenance for screw terminals and inducts galvanic corrosion when coupled with copper without special care. If wiring was properly done and maintained, it is okayish.

[quickthrowman]

If you apply antioxidant paste, torque the terminations to the correct value, and use wiring devices rated for Cu and Al conductors, there are zero problems.

Most homeowners know none of the requirements of aluminum wire installation so I don’t recommend using it, oxidation is bad and can cause fires. Just pay for copper NM cable, it’s dirt cheap anyways.

FWIW I sell and run electrical work for a living. I assume crote and amluto work in the electrical industry, since they’re the only other posters in this discussion who know what they’re talking about.

[Analemma_]

It’s a fire hazard in residential houses where people frequently do their own wiring, because it needs more expertise to wire correctly. Copper wiring is a lot more forgiving to being hooked up by amateurs.

The biggest reason is that aluminum oxidizes, and unlike copper, the oxide layer has high resistivity. In theory that shouldn’t be an issue in datacenters hiring expert technicians.

[pixl97]

Yea, in a data center setup the cost difference can justify the things like soldiering connections rather than mechanical connectors with a higher resistance.

[MSFT_Edging]

Old aluminum wiring in your walls with cloth insulators, designed for a time where electricity consumption was a small fraction of today's electrified usage is dangerous because you're overloading an old, unprepared system.

Aluminum bus bars(solid, often exposed) would be designed for the required power levels and installation criteria.

[Aurornis]

Aluminum home wiring was from the 60s and 70s. It’s not the same as cloth covered knob and tube from earlier years. It has its own problems, but I’d take a house with knob and tube over a house with aluminum wiring.

[margalabargala]

Household electrical usage has decreased, not increased, since that time. Your scaling is backwards.

Old aluminum wires in your walls were designed for a time when you lit your home with 100 watt incandescent lamps rather than 12 watt LEDs.

[quesera]

Only true for lighting circuits though, and most household circuits are mixed.

The quantity and (edit: aggregate) power draw of modern appliances is far greater now than 60 years ago, so the overall load on the old wires is much higher.

[Jblx2]

> power draw of modern appliances

Here's a article that claims that refrigerator energy efficiency has improved dramatically from 1972 to 2012.

https://appliance-standards.org/blog/how-your-refrigerator-h...

I'd bet that modern TVs are more efficient that CRT televisions. Do most people even have desktop computers anymore, or have they mostly been replaced by laptops, tables, and phones? I'd be interested to see the efficiency numbers for electric clothes dryers over time. I wouldn't be surprised if they are also slightly more efficient than older models, even if they are still using resistance heating. Due to smarter electronics that automatically turn the unit off after the clothes are dry (air humidity sensor). I think electric ranges, dish washers, toasters and coffee machines have been ubiquitous since the 1960s (but are probably about the same energy-consumption wise). Air conditioning units are one thing that I'd believe are much more common today than in the 1970s and 1980s. Household sizes are also smaller, so less electricity used for electric water heaters, and the oven, etc.. Electric vehicles are an up and coming user of electricity. What other appliances are likely to be using more now than before?

[quesera]

These are good points, but having worked on a few older houses, I usually see overextended and overloaded circuits, not the opposite.

Standard small-house service used to be 60A, sometimes as few as 4 circuits! It's now 100A minimum by code, with 200A common.

Ovens/ranges have gone from 30A to 50A (dedicated) circuits by code. Microwaves also require dedicated circuits now. Gaming computers with big GPUs are common. Air fryers and electric pressure cookers are newly-common countertop appliances. People definitely use resistive electric space heaters more now (very cheap, much safer than the older options). And there's a trend away from gas and to electric ranges and water heaters. Heat pumps are also increasingly common. You mentioned air conditioners and EV chargers. Kitchens and bathrooms are now required to have dedicated (and GFCI) circuits. Household sizes are smaller, but houses are larger.

So I guess I'd say that, properly expanded, individual circuits should carry less current than they used to. But very often, appliances (AC, microwave, gaming rig, air fryers), are just "plugged in" to an unexpanded system, with varying results.

If you're lucky, they pop a breaker and you call an electrician. If you're not lucky, they push the power draw into uncomfortable zones, esp for Al wire.

[quickthrowman]

This is absolutely not true in areas where heating the air and water and cooking are done with natural gas. Every single appliance in a house is more efficient today than in 1970 due to advances in motor speed control, without exception. The only thing that didn’t get more efficient is electric resistive heat and it’s impossible to improve on that anyways.

I can’t think of a single appliance from 1970 that consumes less energy than its modern equivalent. Anything with a pump or fan is more efficient and so is lighting. LCD TVs use less energy than CRTs.

I also can’t think of an appliance that has become common in households that draws more than 100 watts of continuous load since the 1970 aside from just ‘computers’. An ancient 500W 80% efficiency PSU at max load only has 5.2A of current at 120V single-phase.

If you convert your natural gas furnace to a heat pump, you will use more electricity but excluding that and NG to electric HPWHs leaves only more efficient equipment.

[quesera]

Sure, but there are more appliances plugged in today than there were. The simplest evidence for this is that there are never enough outlets in an old (unrenovated) home.

In a renovated house, you won't have aluminum wire at all, so these concerns are null.

My original statement should be qualified. Since we were talking about aluminum wire it's relevant -- an updated house will have new (copper) circuits that can handle all this stuff. An NON updated house might have Al wire and be overloaded in a more severe way than it was in the 60s.

But FWIW, new >100W appliances:

  - microwaves (1200+W)
  - air fryers (1500W)
  - electric pressure cookers
  - rice cookers (mine claims 610W on the plate)
  - stand mixers (old: 80W, new: 475W)
  - desktop computers (esp gaming rigs)
  - resistive space heaters (1500W)
  - *bigger* TVs (compare 72" LCD to 19" CRT?)
  - air purifiers (mine clocks 175W on high)
  - towel warmers? :)
  - and the ubiquity of 10-20W small stuff has of course exploded, and it all adds up

[knollimar]

Old aluminum is dangerous. Modern aa-8000 series aluminum is fine. Bigger pipes though.

[nerdralph]

Most residential 200A electrical panels use tin plated aluminum busbars. https://www.eaton.com/cr/en-us/catalog/power-connections/bus...

[quickthrowman]

Most commercial panelboards and transformers also use aluminum buss.

[pfdietz]

One good reason for moving from copper to aluminum is that copper contaminates recycled steel, but aluminum doesn't. Fortunately these days it's profitable to carefully extract most of the copper wire and such from scrap steel before it's melted down.

[zahlman]

> In the Earth's crust, aluminium is the most abundant metallic element (8.23% by mass[68]) and the third most abundant of all elements (after oxygen and silicon).

TIL. I thought it would be relatively expensive due to the difficulty of extracting it.

(Iron is much cheaper than I thought, too.)

[crote]

It used to be extremely expensive!

The Washington Monument has an aluminum cap, which at the time was as expensive as silver. Two years later the Hall-Héroult process was invented, and as a result the price plummeted.

[newyankee]

Aluminium essentially reflects electricity prices and increasingly recycled

[candiddevmike]

AFAIK Aluminum wires will become a heat liability, especially at higher amps

[crote]

That's why my calculation example used a 1.5mm2 copper wire but a 2.4mm2 aluminum one.

Aluminum has a higher resistance, which means the same diameter will get hotter than copper. Make the cable thicker and its resistance drops, which means it gets less hot.

Want more amps at the same temperature? Ohm's law still applies: just use a thicker cable.

[pfdietz]

Aluminum has lower resistance per kg, or per $. This is why transmission lines use aluminum (around a steel core).

[greggyb]

Any wire---of any non superconducting material---will be hotter at higher current flows. You size the wire to the application.

[quickthrowman]

You are incorrect.

Wire can be used for up to whatever ampacity is listed for that size wire and temperature rating in Table 310.16 (Conductor Ampacity) Copper and aluminum have separate ampacity tables because you need to use larger aluminum conductors.

Example:

#250MCM THHN copper can handle 255A in a commercial setting (75C column)

#250MCM THHN aluminum can handle 205A in a commercial setting (75C column).

NEC ampacity table: https://media.distributordatasolutions.com/ThomasAndBetts/v2...

[mmulqueen]

It depends on design, environment and maintenance. If it's well protected against oxidation and it's static, it's not really a problem. Heat issues are often at the joints, which are most vulnerable, but can be coated and encapsulated to mitigate. For some uses, aluminium is superior to copper all things considered. Obviously the diameter of the wire/cable depends on which conductor you use, AC/DC, current and service temp - for some applications, that may favour one material over the other.

[MSFT_Edging]

If the two wires are the same gauge, yes. If you size up the aluminum, at the same resistance/current would mean the same amount of power over the length of the conductor and same heat.

[lillecarl]

Thicker cables or higher voltage(lower current) is the answer which is why it's used in power distribution networks where they can control the voltage by planning what to transform to.

[kmbfjr]

Aluminum conductors are dangerous unless the entire system is designed for it. It is not a case of switching to something cheaper.

Look at the electrical fires of the 1950’s and 1960’s as an example, and that was at household levels of current.

Aluminum is used, but everything accounts for the insane coefficient of linear expansion and other annoying properties.

[greggyb]

I would imagine most large-scale data center construction projects will include electrical engineers to design the electrical subsystem. A rack's floor footprint is a few square feet. You can put several million dollars of hardware into that rack. A data center will have at least a few racks. It's a very reasonable investment to bring someone in to do electrical design.

[knollimar]

This isn't true at all unless you narrowly dwfine "the entire system".

Each feeder can be aluminum if you put special goop on any copper connections. Breakers accept it just fine, etc.

You should avoid it for smaller wiring, though. There's special 8000 series aluminum if you're trying to be serious with Al feeders

[amluto]

The goop is generally considered to be unnecessary. What you need is a termination that is rated for aluminum wire, and these are very, very common as long as the wire in question is fairly large (8AWG or so and larger).

[knollimar]

I only put it in the comment since the commenters here seemed uninformed.

It's better to be safe and follow specs; it's more when you're doing some compound splice where it makes sense. I figure it'll make more people feel easy about it if there's a preventative measure

[nirui]

> In reality copper is just convenient. We use it because it's easy to work with, a great conductor, and (until recently) quite affordable

It's convenient, it's easy to work with, great conductivity, and cheap enough all at the sametime... Dude, I think you just explained why cropper is used instead of anything else.

[jandrese]

> and cheap enough

Not anymore. :(

[quickthrowman]

Wire has barely gone up in price, I was paying $175 for 1000’ of #12 THHN a year ago and today it’s about $190 for 1000’ of #12 THHN.

It’d be nice to get 1000’ of 12-2 MC cable for $500 again, but those days are gone.

[amluto]

> Sure, aluminum is a pain to work with

Really? In larger sizes, an equivalent ampacity aluminum cable is generally lighter and more flexible than copper. The main downside is that it’s thicker.

(Common terminations for larger wire sizes are often dual-rated for aluminum and copper. The engineering details for how to design lugs that work well for aluminum and copper were worked out long ago.)

[fedeb95]

interesting, thanks!