Installing NEMA 14-50. Is 8 gauge wire crazy?

rfmurphy81 · Jan 18, 2016

Hi everyone,

I'm having an electrician put in a new 50 foot run from my panel to garage ending in a 14-50 outlet on Thursdsy. He mentioned putting in an 8 gauge wire, but I swear I read that 6 gauge is better. I've seen conflicting information about whether 8 gauge would be acceptable for my upcoming Model S and possibly needing to reduce the car settings from 40a to something lower. Should I insist that he put in a 6 gauge wire or would 8 gauge wire be acceptable to fully use the single charger on the car? What kind lf cost difference is acceptable? I'm not needing to put in the HPWC but I want to make sure I'm able to charge as much as possible without paying the 2k for the dual charger and the extra costs for the 2 or 3 gauge wire to run 100a to the garage. I would love some advice from all you experts!

Tedkidd · Jan 18, 2016

Think you'll ever want to charge 2 cars?

arnolddeleon · Jan 18, 2016

If the electrician knows what they are doing then it will be the right 8 gauge wire and it will be fine. You can look up the cost differential for wire in your area. The thicker wire can be quite a bit harder to work and I don't recall if a larger conduit would be required. I would expect that electricians would normally quote the most economical solution that will properly do the job since they assume you are shopping on price. You should be able to ask them for their reason for using 8 versus 6, if they can't answer to your satisfaction then you need a new electrician.

arnold

rfmurphy81 · Jan 18, 2016

Great question. At this point, it's unlikely. If there was a second car, we would swap as we each only drive a few miles to and from on the daily commute.

- - - Updated - - -

arnolddeleon said:
If the electrician knows what they are doing then it will be the right 8 gauge wire and it will be fine. You can look up the cost differential for wire in your area. The thicker wire can be quite a bit harder to work and I don't recall if a larger conduit would be required. I would expect that electricians would normally quote the most economical solution that will properly do the job since they assume you are shopping on price. You should be able to ask them for their reason for using 8 versus 6, if they can't answer to your satisfaction then you need a new electrician.

arnold

Should I ask him if the 8 gauge is copper and rated for 50-55a then? Not sure what question to ask to make sure I'm getting the right wire.

David99 · Jan 18, 2016

Larger diameter is always better. It means less resistance = lower losses in the wire = they stay cooler = good! I think the electrician wants to give you a low quote and as long as the wire size is to code, there is nothing wrong with it. I personally like to oversize wires. I like to minimize losses and be on the safe side. And it gives you the option to install a HPWC later if you want to, or hook up two chargers.

Chris TX · Jan 19, 2016

Individual wires (non-Romex) inside conduit might be fine for heat dissipation, but 50' could be pushing it. I stick to 6AWG for all my 50A circuits.

arnolddeleon · Jan 19, 2016

rfmurphy81 said:
Should I ask him if the 8 gauge is copper and rated for 50-55a then? Not sure what question to ask to make sure I'm getting the right wire.

Short: Ask him for the cost for 6 gauge. If it's within your noise budget then go for it.

Long: I found the thread with the discussion here: Wire Gauge Size for 50 Amps

arnold

arnold

GSP · Jan 19, 2016

arnolddeleon said:
Short: Ask him for the cost for 6 gauge. If it's within your noise budget then go for it.

Long: I found the thread with the discussion here: Wire Gauge Size for 50 Amps

arnold

arnold

Great info in that thread. Sounds like the OP is best to go with 6 AWG if the cost is reasonable. Less voltage drop, so slightly faster and more reliable charging, and less heat (wasted electricity and faster degradation of connections).

If going with 8 AWG, then all connections need to be rated for higher temperature, not just the wire. I would go with 6.

GSP

Rocky_H · Jan 19, 2016

Did you look at the install guide for the 14-50 outlet on Tesla’s website? (That’s a rhetorical question.) Click on the Model S page, and then click on charging. At the bottom of the page, they have links to the install guides for both the 14-50 outlet and the HPWC.

And why didn’t any of you replying with your opinions just give the link to it? Here’s what the install guide says:
“Conductors:6 AWG, Copper Wire Only. Upsize wiring for installations over 150 feet”

https://www.teslamotors.com/sites/default/files/downloads/US/universalmobileconnector_nema_14-50.pdf

Opinions are cool for some things, but when there is a clear authoritative answer for something, how about we go ahead and give that?

rfmurphy81 · Jan 19, 2016

Thanks for the responses all, and pointing me to the Tesla 14-50 guide, Rocky_H. I saw it previously but this just re-emphasizes that I need 6 AWG.

jcaspar · Jan 19, 2016

When I wired my garage I ran 2/3 to a 100 amp panel and 6/3 to each of two 14-50 outlets. I used NM-B type (3 wires plus ground wrapped together) as it is much easier for me to work with as a non-electrician. I did not want to use conduit as I wanted a clean installation and hate the look of exposed conduit. I could have downsized one wire size if I used conduit and separate wires.

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Installing NEMA 14-50. Is 8 gauge wire crazy?

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