So my electrician was planning to run 60 feet of aluminum wire from my fuse box to the garage and he said if he makes the wire thicker it will be as good as copper and save me a few hundred bucks. This house, I’m only gonna be here a few more years so don’t need the best however I want to get the 25-30 miles/hour charge rate. My dad, an EE and not a fan of Tesla/EVs, said to go with copper because he said the resistivity of Al was “twice that of copper” and that I would have to spend more on my electricity bill cf copper due to electrical losses related to heat. I’m a life sciences kinda guy (physician) and electrical things have always sorta been my kryptonite so just curious if this is true in reality.
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Aluminum vs Copper NEMA 14-50
- Thread starter cryovain
- Start date
Your dad is an idiot... and I mean that in a kind way.
Cerrowire Resources - Ampacity Charts
Aluminum's resistivity is about 50% more than copper. It is indeed fairly common to upsize aluminum conductors for the same resistance or ampacity over a distance.
You plan to put in a 14-50, so I assume you are planning a 50 amp circuit(of which you'll actually only use 32, since the UMC is limited to 32).
Voltage Drop Calculator | Southwire is a decent resource. It shows that for 8 gauge copper, the resistance will be 0.7421 ohms per 1000 feet, or 2.652 volts for your 60 foot run, which is 85 watts of heat lost in the wire(2.65*32). Using 8 gauge ALUMINUM gets you 1.236 ohms per 1000 feet, or 4.357 volts loss for the 60 feet(139 watts). Upsizing to 6 gauge AL gets you 0.77 ohms per 1000 feet, or 88 watts of heat lost. Those heat losses may seem large, but keep in mind that the car is getting around 7700 watts at that same time.
So yeah, with upsized AL conductors, you lose 3 more watts out of ~7700 delivered.
Visiting Wire & Cable Your Way | Electrical Wire By the Foot, I see 6-3 copper for $4.53/ft, or 4-3 aluminum SER cable for 2.52/ft
Cerrowire Resources - Ampacity Charts
Aluminum's resistivity is about 50% more than copper. It is indeed fairly common to upsize aluminum conductors for the same resistance or ampacity over a distance.
You plan to put in a 14-50, so I assume you are planning a 50 amp circuit(of which you'll actually only use 32, since the UMC is limited to 32).
Voltage Drop Calculator | Southwire is a decent resource. It shows that for 8 gauge copper, the resistance will be 0.7421 ohms per 1000 feet, or 2.652 volts for your 60 foot run, which is 85 watts of heat lost in the wire(2.65*32). Using 8 gauge ALUMINUM gets you 1.236 ohms per 1000 feet, or 4.357 volts loss for the 60 feet(139 watts). Upsizing to 6 gauge AL gets you 0.77 ohms per 1000 feet, or 88 watts of heat lost. Those heat losses may seem large, but keep in mind that the car is getting around 7700 watts at that same time.
So yeah, with upsized AL conductors, you lose 3 more watts out of ~7700 delivered.
Visiting Wire & Cable Your Way | Electrical Wire By the Foot, I see 6-3 copper for $4.53/ft, or 4-3 aluminum SER cable for 2.52/ft
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Your electrician is correct but may be either overlooking or missing some details. Every EV installation is highly recommended to be copper- only, in the instructions. In addition, the connectors at the breaker panel and the recepticle MUST be AL compatible. I would assume every good electrician knows this, however I would not go against every manufacturer's recommendation of copper only.
I would accept that he could run AL to a separate sub-panel, which would then connect to your recepticle or wall connector with copper, but negates most of your savings. The power-loss is negligible compared to a home-loss to fire.
roblab
Active Member
I've never been a fan of doing things based on how much money I'd save but rather how good the job got done. Copper does a better job. The only people that want you to use Aluminum are the aluminum people. Do it right and you won't be sorry.
BTW, I'm also in the Copper-only camp, but I'm not an electrician by trade(far from it!). If its going through conduit, it would be fine to put in a 6-50 outlet and avoid the neutral, which saves you around 1/3 of the overall conductor cost. Technically, even if its NOT going through conduit its fine to put in 6-2 NMB at $3.39/ft, its just sort of a problem when the next owner wants to turn it into a 14-50 and needs a whole new line installed instead of just pulling a neutral through the conduit.
In approximate terms, and without electrician markup, its around $120 more for the Cu.
Kimmi
Member
stopcrazypp
Well-Known Member
Yep, Tesla recommends copper for 14-50 also, when used in conjunction with the mobile connector:
"Conductors: 6 AWG copper wire for circuits up to 150 feet"
https://www.tesla.com/sites/default/files/pdfs/installation-guides/nema-14-50-installation-guide.pdf
The 9450FR outlet which is quite popular also is only rated for copper only:
https://hciapps.hubbell.com/hcipunchout/LiteraturePDFS/3B/Original_BSS57.pdf
There was a previous discussion that brought out NEC requirements:
"110.3(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling."
Is it safe to use 70 amp breakers for home wall connectors to charge Model 3?
Sure, the chances of an inspector (either during inspection for the install or for insurance if your house burns down) discovering such a difference is low, but might not be worth it.
For OP, I would make sure exactly how much money you save from going to aluminum, as 60ft isn't too long a run. From above, if "6-3 copper for $4.53/ft, or 4-3 aluminum SER cable for $2.52/ft". Copper costs $272, Aluminum costs $151, so you only save about $120 in materials.
For myself, going with copper would be no brainer for such a small difference, especially given you can be pretty much sure everything that goes with it is compatible. It also makes pulling and installing much easier. #6 fits just right in a standard sized box for a 14-50 (I did mine DIY), #4 may be much harder. And don't forget box size calculations (which your electrician will do):
Master Thread: Definitive 14-50 NEMA Outlet Guide
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stopcrazypp
Well-Known Member
If they bump up the size from #6 copper to #4 aluminum there shouldn't really be much difference in actual fire risk (or even energy consumption). The difference is if a fire happens because of something else, and the insurance inspector finds out about this difference, you may end up not getting coverage, because they can blame you for not following manufacturer instructions (which is required by NEC).
Of course, the chances of that is low, but it's up to you to find out the exact cost difference (as calculated above, from others numbers for material costs, the difference is about $120 for pure materials cost for a 60ft run) and if it's worth it to risk it. Your electrician may have margin on top, or have more of some particular material available, so the cost difference may be different than calculated above.
AL is the sacrificial metal in a panel. I it Will corrode. If installed properly in will last longer but eventually it will fail.
Thanks for the replies. It’s only a few hundred collars difference as noted above so am just going to go with copper. My electrician made it seem like it was a no brainer to save some money with aluminum so I was just curious the pros/cons and the risks are too high not to do it for such a low cost difference. Thanks again.
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