Dispute with my NEMA 14/50 outlet installer. Help.

[Racerx22b]

I hired an electrical contractor in my city with a very positive rating and history. They have installed about 10 outlets for Teslas. He stated he was familiar with the install guidelines so I didn't think I had to school him on it (my mistake). During installation I walked out while wire was being pulled and noted it was 8 gauge. Since it was in my mind that 6g was used by most people on here, I questioned the installer and he said 8g was the wire required for a 50amp breaker. FWIW, my wire run is about 25'.

Since then I've spoke with the company owner and was also assured this was the correct wire per code (or whatever official guidelines they follow).

Obviously, the install guidelines from Tesla say otherwise.

Questions:

1. Other than Tesla's install guidelines, are there any official guidelines to dispute their claims? I've googled it and while most people prefer 6g I've found no official guidelines that support the need for 6g.
2. If I stay with 8g will there be any issues with charging at 40amps due to the onboard chargers detecting some type of deficiency?
3. Does anyone have 8g wire with their 14/50 outlet? Any issues?
4. Anything I'm not thinking of?

I appreciate opinion but I'm really looking for hard facts to back the necessity for 6g. I'll need it if I need the contractor to change out the wiring.

Heres a link that supports the use of 8g.

Determining Proper Electrical Wiring Size

 

[Cosmacelf]

Depending on the exact temperature rating on the wire, 8 gauge can be code compliant. I've used it myself, and it works just fine. Is your wire in conduit or romex?

 

[jerry33]

Read FlasherZ's FAQ on electrical installation. "WHAT WIRE SIZES SHOULD BE USED FOR INSTALLING MY NEMA 14-50R?

Note: All wire sizes assume copper conductors!

For wire-in-conduit, 8 AWG THHN (dry locations) or THWN (wet locations) is sufficient to carry 50 amps, but many electricians will use 6 AWG to ensure that there is enough headroom. The ground conductor must be a minimum size of 10 AWG.

For “Romex” (NM-B cable), it must be sized for the 60 degC rating. This means that 8/3+ground NM-B may not be used for 50A, and 6/3+ground NM-B must be used. Note that type NM cable must be protected from damage (e.g., must be run inside a wall) and cannot be exposed. If you must run wiring on the outside of a wall, below 7' above the floor, you must use conduit. Type NM cable may be run in conduit as long as it does not run outside.

If these conductors will ride in the same conduit as another circuit, they must be “de-rated” and 6 AWG is required."

 

[Lloyd]

With a 25' run, you will have about a 3% voltage drop max. You should be ok. I would have specified 6 wire just because of the continuous duty. More than 50' you should use 6 wire.

http://www.cerrowire.com/voltage-drop-table

 

[Racerx22b]

Read FlasherZ's FAQ on electrical installation. "WHAT WIRE SIZES SHOULD BE USED FOR INSTALLING MY NEMA 14-50R?

Note: All wire sizes assume copper conductors!

For wire-in-conduit, 8 AWG THHN (dry locations) or THWN (wet locations) is sufficient to carry 50 amps, but many electricians will use 6 AWG to ensure that there is enough headroom. The ground conductor must be a minimum size of 10 AWG.

For “Romex” (NM-B cable), it must be sized for the 60 degC rating. This means that 8/3+ground NM-B may not be used for 50A, and 6/3+ground NM-B must be used. Note that type NM cable must be protected from damage (e.g., must be run inside a wall) and cannot be exposed. If you must run wiring on the outside of a wall, below 7' above the floor, you must use conduit. Type NM cable may be run in conduit as long as it does not run outside.

If these conductors will ride in the same conduit as another circuit, they must be “de-rated” and 6 AWG is required."

The wire is in romex for the run through the attic but in conduit from breaker panel into attic then from attic to outlet. Does that change anything?

 

[arondaniel]

I used 6 but my run is closer to 50'. Another consideration, you might not be able to upgrade to a HPWC later with 8 gauge wire.

 

[Park2670]

Same thing happened here. I asked my contractor to put in a 50 amp plug in my garage not thinking about gauge. They installed 8 gauge since it is technically to code.

The unfortunate part is I dont have a Tesla yet. I have been charging my Volt with the 14-50 and a CC LCS-20 but that doesnt even come close to the 40 amps the Tesla does.

 

[scaesare]

I'm currently using #8 (of sufficient temp rating) for my HPWC on a 50A circuit, until I do some panel work (in conjunction with solar) to upgrade to a 100A circuit.

I have about a 50' run. and get a voltage sag of about 3-4%.

Regardless of what wire you run, I recommend checking the torque on all lugs a couple of times in the weeks after installation, a well as ensuring you are getting no hotspots (breakers, wires, disconnects, outlets/boxes, etc...)

 

[NigelM]

The wire is in romex for the run through the attic but in conduit from breaker panel into attic then from attic to outlet. Does that change anything?

No. I believe that's to code here in FL at least.

 

[kota23]

8 awg will be fine for 25' and meets code for 50 amp. I have #8's for my recent installation and have had no issues.

 

[scaesare]

I'm currently using #8 (of sufficient temp rating) for my HPWC on a 50A circuit, until I do some panel work (in conjunction with solar) to upgrade to a 100A circuit.

I have about a 50' run. and get a voltage sag of about 3-4%.

Regardless of what wire you run, I recommend checking the torque on all lugs a couple of times in the weeks after installation, a well as ensuring you are getting no hotspots (breakers, wires, disconnects, outlets/boxes, etc...)

I should add that I ended up with #8 because when I was finishing my basement I ran a few spare circuits to my panel before closing up the sheetrock... one of which was for a future second upstairs AC unit. As this cable was coiled up in my utility closet conveniently adjacent to my garage, that's what I pressed in to service for my interim HPWC installation.

if I were running new cable, I'd go with #6 for a 50A circuit and #2 for a 100A.

 

[qwk]

While 8 gauge is up to code in conduit, the cost difference is pretty small for a 25' run, so any GOOD electrician will go with 6 gauge for a continuous load like an EV.

 

[randompersonx]

Adding to what others said, 8 will work, but 6 is better. With a heavier gauge wire, you will have less resistive loss/voltage drop, so you will save a little bit of money on your charging long term, and charge slightly faster. It's probably not worth the effort to re-do it just for that reason, but something to keep in mind for a future run.

Also like others said, worth checking to make sure all of the connectors are screwed in tightly as that could also be a source of resistive loss.

 

[wycolo]

Electricians do not plan for 10 years ahead. You may want to charge at 80A some day.
--

 

[randompersonx]

Electricians do not plan for 10 years ahead. You may want to charge at 80A some day.
--

Sure, but for 80A he would want 2 gauge anyway, so 6 wouldn't have helped much with that anyway.

 

[TexasEV]

While 8 gauge is up to code in conduit, the cost difference is pretty small for a 25' run, so any GOOD electrician will go with 6 gauge for a continuous load like an EV.

It's a continuous load, but does it make a difference that the continuous load is actually 40A rather than 50A?

 

[Electricfan]

I've been charging my S in my garage for a year and 3 months using my 14-50 outlet, wired with 8 ga wire, no problems yet... I was nervous but bowed to the electrician's experience and let them install 8. If it makes you more comfortable, insist on 6. You have to live with it for years to come - he doesn't.

 

[Racerx22b]

Thanks everyone for the info. Feel better now with just leaving 8g. I actually have a HPWC but will just be setting it up to charge at 40amp. Going to just put a "pig tail" outlet on it to plug into my outlet.

 

[qwk]

It's a continuous load, but does it make a difference that the continuous load is actually 40A rather than 50A?

The only difference it will make is the higher voltage drop, which will heat up a bit more, and use a tiny bit more electricity.

 

[linkster]

The wire is in romex for the run through the attic.......

Huh?

Romex is neither a flexible nor rigid conduit, but a pre-bunded wire set with individually insulated and nylon/PVC jacketed wires with a paper wrap inside including a bare ground that has an outer PVC jacket encompassing the entire bundle.

Sure the wire gauge size matters, but the type (romex vs. THHN) is equally important, as they have very different allowable ampacity ratings for the same size wire gauge. The bottom line is that if you go into your attic and you can read "Romex NM-B" 8-3 on the PVC jacket it must be on a 40 amp breaker and is not to code for the required 50 amp branch circuit that is needed for continuous (more than 3-hrs) charging at 40 amps. If your electrican used 8 gauge THHN or Romex 6-3 (both have a 55 ampacity rating) then you're good.

If you are in doubt, you might call your local electrical inspector.