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Wiring for NEMA 14-50 outlet in garage...need your thoughts

Wiring for NEMA 14-50 outlet in garage...need your thoughts

Hey, all, I have two estimates for installing the NEMA 14-50 outlet in our garage for use with the UMC. The main difference among them is the choice of wiring.

One is proposing to use "#6 Romex," which I assume is 6/3 copper, for $450.

One is proposing to use "#6 SER AL wire type XHHW," which is aluminum and rated for 50Amps at 75'C (per http://www.barr-thorp.com/wp-content/uploads/2011/04/Digest-176-NEC-Tabl...), for $350.

I'm not very jazzed about the idea of aluminum wiring. Anyone with electrical experience have some advice or opinions?

Thanks in advance.

Tom | July 9, 2013

Stick with the copper wire! My experience with aluminum is that it gets hotter, eventually causing high resistance in the connection. P.s. I am not an electrician, but have had poor experience with homes wired with aluminum. PG&E uses aluminum for the supply line. Hope this helps!

jbunn | July 9, 2013

I would stick with the copper. If its romex, should have the w/g designation (with ground), meaning two hots, a neutral, and a ground wire, for 4 wires total. Ground wire can be number 8 copper.

Byong | July 9, 2013

How far is your wire run? and are you putting the wire inside the wall of a finished garage? My understanding on Romex is that it needs to be inside a wall, and not on the outside where it can get damaged. I used 3/4" conduit and ran individual wire inside since I did not want to tear into the drywall of the garage.

mallynb | July 9, 2013

#6 aluminum will get hotter than #6 copper. The conductors are the same diameter. Copper is a better conductor, will have less power loss, and therefore will be more efficient. A better comparison would be #4 aluminum vs #6 copper. The electrician who quoted copper expected a relatively long length of wire or he might have quoted #8.

nickjhowe | July 9, 2013

Best source of info in this is this very comprehensive thread over at TMC. Explains everything:

http://www.teslamotorsclub.com/archive/index.php/t-12615.html

cfOH | July 9, 2013

Thanks for the feedback, all. I am going to insist on #6 copper, although even that can be interpreted in several ways. I appreciate the link, @nickjhowe.

AlMc | July 9, 2013

As people have noted, depending on the distance if I were comparing the two I would compare 6 copper with 4 alum. As people have noted, copper would be my choice.

$450 is reasonable considering the price of copper. I suspect the run is less than 30' for that price.

pdx4s | July 9, 2013

stay away from aluminium if you can, copper has better conductance :

ρ (Ω•m) at 20 °C
Copper 1.68×10−8
Aluminum 2.82×10−8

I used Romex 6 AWG x3 rated for 55amps (Home Depo, ~$2/ft), all parts incl. 50 dual breaker, 5ft of the 6x3 and in wall box for ~$40 at HD. Not recomended to do it by yourself unless you have experience/knowledge of electrical wiring/circuits.

nickjhowe | July 9, 2013

Make sure you think about exactly how the 20' UMC cable will lay/hang in your garage, including the 2' nearest the outlet that contains the controller. People have put the outlet too high or too low without realizing. Check out the link at the start of my Model S delivery checklist for various UMC management solutions.

cfOH | July 9, 2013

@nickjhowe Heh...I spent about 2 hours the other day with an 18' length of heavy extension cord simulating various cord management options in my garage (yes, Tesla-itis is a terrible disease...terrible, delightful disease ;-). I am going to mount the outlet up near the ceiling on a rafter of my garage (about 8' up) near the driver's front fender. That way, I can suspend the UMC using bungies along a ceiling rafter to get it to the charging port regardless of whether I pull in frontways or back in. Having that flexibility is important because I'm not sure how I'm going to prefer trying to get the boat that is my MS into my garage on a daily basis.

nickjhowe | July 9, 2013

+1 @cfOH

EJH | July 9, 2013

I ran #3 wire from the house to a panel in the garage, and then # 6 from the panel to the HPWC. I have 60 amps to the HPWC now, but the #3 allowed me to go up to 100 amps if ever required.

After living with the car for the last few months, I now feel that #6 wire with a 30 or 40 amp breaker is more than adequate for 99% of our needs.

I vote for copper as well.

deezomaxima | July 9, 2013

Copper is the best conductor.

Kleist | July 9, 2013

@deezomaxima - "Copper is the best conductor"... actually Silver is.

Brian H | July 9, 2013

But it has lousy mechanical strength. ;p How about braided aluminum and silver? :)

Kleist | July 9, 2013

Brian - and Silver is too expensive.

Brian H | July 10, 2013

No kidding!?!

frankkoh | June 30, 2015

The problem with aluminum wire is the thermal expansion / contraction. That tends to loosen connections which increases the resistance of the connection. When you run current through resistance it produces heat -- just like a toaster. You can minimize the danger by re-tightening the connections periodically. But are you really going to do that?

The savings are minimal and the danger with AL increases over time. Why take a chance?

Earl and Nagin ... | June 30, 2015

@frankkoh,
My understanding is that the problem with Al is not its thermal expansion/contraction. It is that, unlike Cu, it crushes when squeezed by a connector. Copper, acts like a spring and pushes back, keeping the connector in contact with the copper wire.
An Al connector must have a spring to maintain pressure against the Al wire. Al connectors, then are much more expensive.
Without a spring, for example, just a screw as a connector, the Al will crush a bit and oxide will form between the wire and the connector screw. This oxide is high resistance so heat will be produced. Heat can lead to fire.
Al can be done safely but it takes a lot more effort. It isn't clear that it isn't worth the risk given what is at stake (car, house, lives)

neilhamrin | June 30, 2015

If I were doing it over, I'd stay with the 120V already in the garage. It is more than adequate for my daily usage. Found this out in the rental condo while snowbirding in Ca for 4 months. Went to a sc once a month because of driving visitors.

neilhamrin | June 30, 2015

I should add, in Mn I use my 14-50 mainly as it is metered and priced about half the rest of the home