Calling All Electricians - NEMA 14-50 Power

[JPoldo]

I'm installing a wall outlet 25 feet from the breaker box and wonder if #8 copper wire is sufficient to avoid a large voltage drop causing the charger to drop below 29 amps/hr. I read the charger senses voltage and if too low, reduces charging power significantly to avoid heating conductors. 40 amps through 50 ft (25 ft x 2 wires) produces a 1.24V drop at room temperature per common resistance tables. I prefer #8 over #6 because it's easier to install and lower cost. Will I get maximum charging with #8 wire?

 

[Rockster]

Voltage Drop Calculator

Based on this calculator, you're okay. I tend to err on the side of caution, though. The cost of #6 versus #8 is pretty trivial, all things considered.

 

[Rocky_H]

I'm installing a wall outlet 25 feet from the breaker box and wonder if #8 copper wire is sufficient to avoid a large voltage drop causing the charger to drop below 29 amps/hr. I read the charger senses voltage and if too low, reduces charging power significantly to avoid heating conductors. 40 amps through 50 ft (25 ft x 2 wires) produces a 1.24V drop at room temperature per common resistance tables. I prefer #8 over #6 because it's easier to install and lower cost. Will I get maximum charging with #8 wire?

Don't use 8 wire gauge. Read Tesla's recommended install guide for the 14-50 outlet.

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

"Conductors: 6 AWG, Copper Wire Only. Upsize wiring for installations over 150 feet"

 

[ColdRauv]

#6 AWG minimum is required by NEC unless it is installed in conduit.

 

[JPoldo]

#6 AWG minimum is required by NEC unless it is installed in conduit.

Yes, I am installing it in conduit and trying to understand why Tesla recommends #6 when #8 should work fine at 25 feet. Maybe they are covering much longer distances such as 100-125 feet. #6 wire cost is 50% more at HD / Lowes plus extra labor to pull 4 lines through conduit. Am I "penny wise & pound foolish" considering #8 cable?

 

[davewill]

... Am I "penny wise & pound foolish" considering #8 cable?

Probably. Hey, the #8 is to code, and it should work just fine, but how much extra is the #6, anyway?

BTW, you probably just mistyped, but if you're installing in conduit, you shouldn't be using "cable". They should be separate wires.

 

[mongo]

Yes, I am installing it in conduit and trying to understand why Tesla recommends #6 when #8 should work fine at 25 feet. Maybe they are covering much longer distances such as 100-125 feet. #6 wire cost is 50% more at HD / Lowes plus extra labor to pull 4 lines through conduit. Am I "penny wise & pound foolish" considering #8 cable?

Just for reference, that is because #6 has > 50% more copper per foot/ cross section of 26.250 circular mills vs 16.510.
There are online cut to length wire sources you can price shop.

General tips:
Get a permit.
Use a slightly larger conduit if you are worried about pull, but 25 ft of EMT shouldn't be a problem.
Less bends are easier, 360 degrees is max allowable.
Can use lube to make it easier, don't get in on pull rope.
If you have two people, one to pull on the rope and one to push it is even easier.
Pull all 4 wires at one time.

Minimum size for 50 Amps with 60 degree rating termination is 6 Gauge. 6 and smaller can't be remarked, so you will need a green, white, and either 2 black or a black and red.

 

[JPoldo]

Probably. Hey, the #8 is to code, and it should work just fine, but how much extra is the #6, anyway?

BTW, you probably just mistyped, but if you're installing in conduit, you shouldn't be using "cable". They should be separate wires.

You are correct as I used the wrong term. In conduit, I believe the NEC requires THHN which is about $0.60/ft for #8 and $0.90/ft for #6. Difference in cost is under $50. I simply don't like spending money unless there is some benefit.

 

[brkaus]

Do consider that if you use larger wiring, you can potentially replace the outlet with an HPWC at some point and charge at 48A (60A circuit) sometime in the future w/o pulling new wire. So, $50 now could save in the future.

 

[JPoldo]

Do consider that if you use larger wiring, you can potentially replace the outlet with an HPWC at some point and charge at 48A (60A circuit) sometime in the future w/o pulling new wire. So, $50 now could save in the future.

Thank you ! THAT is an excellent reason for using #6 wire. I am considering a HPWC if the included NEMA14-50 is too slow. If I'm reading the chart correctly, you only get 5 more mi/hr of charging (34 vs. 29) using the HPWC. I'm not sure if the 17% increase is worth $500 to me.

 

[JPoldo]

Mongo, thanks for all the tips as most have worked well for me in the past. Sorry, tip #1 is has no value to me.

 

[brkaus]

Thank you ! THAT is an excellent reason for using #6 wire. I am considering a HPWC if the included NEMA14-50 is too slow. If I'm reading the chart correctly, you only get 5 more mi/hr of charging (34 vs. 29) using the HPWC. I'm not sure if the 17% increase is worth $500 to me.

It is 20% faster, so it is statistically significant. But if it isn't needed, it isn't needed. Still, I like to enable the future opportunity given the minimal extra cost. I'm currently on a 14-15 and doing just fine.

 

[AudubonB]

Can I jump in on this discussion to have someone bring me up to speed with respect to the newer HPWCs and multiple-car charging?

Do I understand correctly that-

• The new HPWCs are set up so that two EVs of differing capacities, charging hardware &c can be ganged onto one HPWC?
• Can one supply 3 vehicles?
• Would a 100-amp circuit still be the appropriate size for same (surely it can't be higher....)?

 

[SageBrush]

You are correct as I used the wrong term. In conduit, I believe the NEC requires THHN which is about $0.60/ft for #8 and $0.90/ft for #6. Difference in cost is under $50. I simply don't like spending money unless there is some benefit.

30 cents per foot * 25 feet = $7.50

Benefits:
Less heat losses -- money in your pocket, less pollution (or more PV.)
Less heat losses, faster charging
Less heat losses, safer operation, better reliability

This is a no-brainer

 

[davedavedave]

30 cents per foot * 25 feet = $7.50

Benefits:
Less heat losses -- money in your pocket, less pollution (or more PV.)
Less heat losses, faster charging
Less heat losses, safer operation, better reliability

This is a no-brainer

And to add to this - OP: I'd wager that based on your hourly income, pondering this question alone cost more than $7.50 worth of your time

 

[ucmndd]

To be fair it’s $7.50 x 4 wires, so we’re talking a whopping $30 - but the point still stands.

 

[brkaus]

Can I jump in on this discussion to have someone bring me up to speed with respect to the newer HPWCs and multiple-car charging?

Do I understand correctly that-

• The new HPWCs are set up so that two EVs of differing capacities, charging hardware &c can be ganged onto one HPWC?
• Can one supply 3 vehicles?
• Would a 100-amp circuit still be the appropriate size for same (surely it can't be higher....)?

There are a few threads around on how the HPWC operates. Let me see if I can cover it quickly -

- Each HPWC can only be connected to one car at a time.
- An HPWC can support different types of Tesla cars, and will charge at the rate the car accepts... up to the configuration of the HPWC (set by a dial inside based on breaker/wiring).
- If you have limited power capacity, multiple (up to 4) can be wired together to share a specified amount of power
(example - if you only have 50a available in your house, you could connect 4 HPWC to that breaker, wire the HPWC together with a control wire, and they will ensure they max out at 40a for all 4 at any given time).

I'm not sure on the algorithm on how it shares.

 

[jsmay311]

Not an electrician, but I'll hijack the call with some snooty responses anyway....

wonder if #8 copper wire is sufficient to avoid a large voltage drop causing the charger to drop below 29 amps/hr.

"Amps/hr" isn't a thing.

I prefer #8 over #6 because it's easier to install and lower cost.

Is it really significantly easier? Over that short of a distance?

To be fair it’s $7.50 x 4 wires, so we’re talking a whopping $30 - but the point still stands.

I think you can install a smaller ground wire. So maybe only save $25 or so.

And the 6AWG would reduce losses by ~0.4%. So you could recoup that $25 over, say, 200,000 miles worth of driving and charging. Then after that it's all profit!

And lastly, OP, cool zip code!

 

[gregd]

I'd recommend the #6. High power stuff is best over-built if you can, just for peace of mind if nothing else.

I had a 35' run to the panel for a new 14-50 outlet, and chose to pull #4-3+ground cable even though #6 would be adequate. It was annoying stringing it (the run was almost all under the house, tacked up to the joists), and very annoying dealing with it in the box with the outlet. But the result is that I have virtually no voltage drop, and I have the ability to simply upgrade the breaker and add an HPWC (or even two, if I were to get a second EV) without having to re-string any wires.

 

[ColdRauv]

OK, if you're in penny-pinching mode, you could eliminate the ground wire and use the EMT as the equipment ground (not recommended) or go with a #10 THHN green ground.